Jiten Jha

Linux Basic Commands

2015-12-01T19:48:00.001+05:30

How to change Shell in Linux?

cat /etc/shells (In that file you will see all shell that support by OS)
To change Shell "chsh -s /bin/shell name" "chsh -s /bin/tcsh"
Change Shell for user "chsh -s /bin/shell name Username" "chsh -s /bin/tcsh jiten"

What is the command to check user group name , group ID , UID ?

id username

id jiten (This command will show you UID , GID , group name)

What is the command to check user account expiry date info?

chage -l username

chage -l jiten (This command will show you user related information)

User add command options?

what is the command to create user in different directory?

useradd -d /home/directory name/ username username

useradd -d /home/sale/jiten jiten

what is the command to user with specific user ID?

useradd -u UID number user name

useradd -u 2222 jiten

what is the command to user with specific GID?

useradd -u UID number -g GID number username

useradd -u 3323 -g 400 jiten

useradd -g 391 jiten

what is the command to add user in multiple group?

useradd -G group name username

useradd -G postfix,sale,market jiten

(To separate groups we use "," sign )

what is the command to add user without HOME directory?

useradd -M username

useradd -M jiten

what is the command to add user with account expiry date?

useradd -e yyyy-mm-dd username

useradd -e 2013-06-01 jiten

what is the command to set user expiry date and days?

useradd -e 2013-06-01 -f 45 (days) username

useradd -e 2013-06-01 -f 45 jiten (user command with expiry in 45 days)

what is the command to set comment on user ?

useradd -c "Hello I am sales team" user name

useradd -c "Hello I am sales team" jiten

what is the command to change user shell?

useradd -s /sbin/nologin username

useradd -s /sbin/nologin jiten

Add user with specific Home directory , Default shell and Custom comment?

useradd -m -d /home/sales/username -s /bin/bash -c "sales person" -U username

useradd -m -d /home/sales/jiten -s /bin/bash -c "sales person" -U jiten

Add user with home directory, custom shell , custom comment and UID/GID?

useradd -m -d /home/sales/username -s /bin/bash -c "hello" -u 6000 -g 6000 username

useradd -m -d /home/sales/jiten -s /bin/bash -c "hello" -u 6000 -g 6000 jiten

Add user with home directory , no shell , custom comment and UID?

useradd -m -d /home/sales/username -s /sbin/nologin -c "how are you team" -u 1020 username

useradd -m -d /home/sales/jiten -s /sbin/nologin -c "How are you team" -u 1020 jiten

Add user with home directory, shell,custom skell/comment and user ID?

useradd -m -d /home/sales/username -k /etc/custom.skell -s /sbin/tcsh -c "sales member" -u 3021 username

useradd -m -d /home/sales/jiten -k /etc/custom.skell -s /sbin/tcsh -c "sales member" -u 3021 jiten

Add user without home directory, No shell and no group ?

useradd -M -N -r -s /bin/false username

useradd -M -N -r -s /bin/false jiten

What is the usermod command and it use ?

we use usermod command to modify user details

what is the command to change user home directory ?

usermod -d newdirectory name olddirectoryname

usermod -d /home/testnet jiten (This command will not copy the content of jiten user directory to testnet directory)

what is the command to change user home directory with it content?

usermod -d newdirectory name -m olddirectory name

usermod -d /home/testnet -m jiten (When you will run this command it will copy jiten directory content to testnet directory)

what is the command to add group in user?

usermod -G group name user name

usermod -G developer jiten

what is the command to add group with exist group?

usermod -aG groupname username

usermod -aG developer jiten

what is the command to change user primary group?

usermod -g groupname username

usermod -g developer jiten

id username

id jiten

what is the command to lock user?

usermod -L username

usermod -L jiten

what is the command to unlocking user?

usermod -U username

usermod -U jiten

what is the command to change expiry date of user account?

usermod -e yyyy-mm-dd username

usermod -e 2016-12-30 jiten

what is the command to change login name ?

usermod -l newname username

usermod -l jitenjha jiten

what is the command to change login password?

usermod -p newpassword username

usermod -p newpassword jiten

what is the command to change user shell?

usermod -s /bin/bash username

usermod -s /bin/bash jiten

Squid Proxy with Mysql Auth

2014-01-23T12:23:00.002+05:30

Configure Squid Proxy server :

1. Install Squid, start it, and set it to start on boot.

$ su -

# yum install squid

# service squid start

# chkconfig squid on

2. Now install SquidGuard.

# yum install squidGuard

3. Now that SquidGuard is installed, open Firefox and go to the SquidGuard website: http://squidguard.org . The SquidGuard website has links to configuration documentation and websites to download blacklists. You need to download a blacklists file. You can go to http://dsi.utcapitole.fr/blacklists/ and get the link for the blacklists.tar.gz file, then you can use wget to download blacklists.tar.gz, by copying and pasting the link, or you can download it through the Firefox web browser. Squidguard has its own blacklists.tar.gz file, and you will eventually want to replace it with the newer blacklists.tar.gz file that you downloaded. Before you do that, you can create a test blacklists file for SquidGuard to block. To do that you need to create a blacklists directory in the /var/squidGuard/ directory. Now, in the new blacklists directory use vim create and edit a text file called testdomains.

# cd /var/squidGuard# mkdir blacklists
# cd blacklists
# mkdir testdomains
# cd testdomains
# vim testdomains

4. In this testdomains file you have write or add website name those you want to block.type in three lines of text to add some test-domains to block:
yahoo.com
msn.com
whatever-you-want-to-block.com

save and exit.

5. After create testdomains file Now you have to edit squid.conf file.

6. vim /etc/squid/squid.conf

7. If you have LDAP server so add this lines :

## LDAP AUTH

auth_param basic program /usr/lib64/squid/squid_ldap_auth -b "dc=ii,dc=ac,dc=in" -f "uid=%s" -h ldap.ii.ac.in

acl ldapauth proxy_auth REQUIRED

http_access allow ldapauth

(/usr/lib64/squid/squid_ldap_auth) This line represent that all

squid commands in /usr/lib64/squid/ directory

8. Make sure that you have to put right path so that command will execute .

9. Squid normally listens to port 3128
http_port 8080
Find line listens port 3128 .
If you want to change port no. so you can change it.

10. url_rewrite_program /usr/bin/squidGuard -c /etc/squid/squidGuard.conf

write this 2 lines in squid.conf file .
/usr/bin/squidGuard is a command and /etc/squid/squidGuard.conf is the squidGuard configuration file path.

redirect_children 20

11. save and exit squid.conf file.

12. vim /etc/squid/squidGuard.conf

When you open squidGuard.conf file .

13. dbhome /var/squidGuard/blacklists

14. remove blacklists and line look like.

dbhome /var/squidGuard

search and edit

15. dest adult {

domainlist blacklists/testdomains/testdomains

urllist blacklists/terstdomains/testdomains

expressionlist blacklists/porn/expressions

}

16. Add :
default {

pass !testdomains any

# rewrite dmz

redirect http://10.99.100.3/blocked.html

}
here you will see redirect option if you want you can delete it or you can put any website name , any html page that will so some message.

17. Authenticate from MySQL database

18. yum search mysql-server

19. /etc/init.d/mysqld restart

If you face any problem to start it. vim /etc/my.cnf file and change "datadir=/home/mysql" path or locate , file name.

20. mysql -u root -p

21. create database squid;

22. grant select on squid.* to dataproxy@localhost identified by 'dataproxy';

If you want to can allow dataproxy user permission for check or edit squid database.or you can use root user.

23. Create table 'passwd' in 'squid' db.

CREATE TABLE `passwd` ( `user` varchar(32) NOT NULL default '', `password` varchar(35) NOT NULL default '',`enabled` tinyint(1) NOT NULL default '1', `fullname` varchar(60) default NULL, `comment` varchar(60) default NULL, PRIMARY KEY (`user`) );

24. Populate the table with some test data, eg
insert into passwd values('testuser','test',1,'Test User','for testing purpose');
In the insert line 'testuser' is a user name and 'test' password for access internet.

25. Again Edit squid.conf file.

26. vim /etc/squid/squid.conf

auth_param basic program

/usr/lib64/squid/squid_db_auth --user dataproxy --password dataproxy -- plaintext --persist
auth_param basic children 5
auth_param basic realm Web-Proxy
auth_param basic credentialsttl 1 minute
auth_param basic casesensitive off
acl db-auth proxy_auth REQUIRED

http_access allow db-auth
http_access allow localhost
http_access deny all

27.save and exit file.

28. Now compile the SquidGuard blacklists and chown the blacklists to be accessible by Squid.

squidGuard -b -d -C all

chown -R squid /var/squidGuard/blacklists

29. restart squid service

/etc/init.d/squid restart

30. At last open terminal

Run this command for testing

/usr/lib64/squid/squid_db_auth --user dataproxy --password dataproxy -- plaintext --persist --- Press Enter

After Press Enter you have to put username and password there like we have created testuser test

username and password both in same line with one space. you will see ok it mean it is working fine.or any error so send me or you can google it.

32. OPEN your browser firefox , internet explore , chrome,

33. Proxy setting option

34. Manual Proxy setting

35. put there your squid server ip address or domain name if it is and port no that you allow or open it.

Best of Luck

PostgreSQL

2012-03-09T10:53:00.000+05:30

POSTGRESQL

aptitude search postgresql

You have to install server type & latest version of SQL server.

Run postgresql command

apt-get install postgresql name ( package name with version )
                       or
aptitude install package name

After that we check postgresql is working or not
"psql : FATAL: role "root" does not exits

# psql postgres

# su - postgres

# pwd to check path of file.
    /var/lib/postgresql

#postgres@common-...:~$ su - postgres
#createuser -U postgres -P

Connect to database or access any database

#psql postgres ( database name )
postgres => [ postgres is bydefault database create when we install postgresql ]

To see database "\l"
To quit to database "\q"
Create database in postgresql
#createdb data1 ( database name ) ---> This command run in user mode.

postgres => CREATE DATABASE data1;
postgres => \l
Stop any process in sql ";"

Connect to other database
psqlgres => \c [ database name ] data1

Alt + F1 : open application menu
Alt + F2 : Display run application dialog
print screen : Take a screen shot of the entire desktop
Alt + print screen : Take a screen shot of the current open windows
Ctrl + Alt + Arrow : switch to the work space to the specified direction of
                                 the current workspace.
Ctrl + Alt + D : Minimize all windows & give focus to the desktop
Alt + tab : Switch between windows. A list of windows that you can select is display id. Release the keys to select a windows. You can press the "shift" key to cycle through the windows in reverse order.
Ctrl + Alt + Tab : Switch the focus between the panels and the desktop. A list of    items that you can select it display. Release the keys to select
                             on item. you can press the "shift" key to cycle through
                         the items in reverse order.

PS command

2012-03-07T11:13:00.004+05:30

ps command

use for check which process is run or not.

#ps -ef ---> show you all process running on computer
# ps -ef | grep -i process name ----> grep any process you want to check or kill.

If you want to set any value to any file then we run .

echo [ 1 or 0 ] > /proc/sys/net/ipv4/ip_forward

echo is command
1 or 0 is value
/proc/sys/net/ipv4/ip_forward --> file path

APT ( Advanced Packaging Tool )

2012-03-07T11:08:00.005+05:30

APT ( Advanced Packaging Tool )

apt-get   -------> APT package handling tool
apt-get install (package name) ----------> To install any software and package

apt-get install firefox

apt-get autoremove package name
apt-get remove package name --------------> To remove package

* aptitude :-> high-level interface to the package manager This command use
                      for.

                    install any software or find any software.

aptitude search ( package name ) ----> search any package
aptitude install ( package name ) -----> To install any package
aptitude remove ( package name ) ----> To remove any package

If you want to install any binary package like java in a binary formate then give package execute permission. After that [ ./java ] is command.
./java

Check java install or not :

dpkg -query -l | grep java

This command show you that the java install or not check java package install or not.

env : run a program in a modified environment
         This command run for to check environment or path is correct or not.

export JAVA_HOME = /opt/java
export = command
JAVA_HOME = variable
/opt/java = file location

export JAVA_HOME = /opt/java
export ANT_HOME = /opt/ant ----> [ ANT is a compiler ]
echo $ JAVA_HOME
echo $ANT_HOME -----> To check variable export or not.

vim /etc/profile ----> insert line

export JAVA_HOME = /opt/java
export ANT_HOME = /opt/ant
export PATH = $PATH:${JAVA_HOME}/bin:${ANT_HOME}/bin ---> restart pc

But if you don't want to reboot pc then run
   [ source /etc/profile ] -----> command use for execute variable .

Proc File System

2012-03-06T17:57:00.000+05:30

Understanding the Proc File System

The Linux kernel provides a mechanism to access its underlying internal data-structure and also to change its kernel setting at run-time through /proc file system. We will be discussing the /proc file system here targeted to the Intel x86 architecture; though the basic concepts will remain the same for linux on any plarform.

/proc - a Virtual File System:

The /proc file system is a mechanism that is used for the kernel and kernel modules to send information to processes ( hence the name /proc ). This pseudo file system allows you to interact with the internal data-structure of the kernel,bet useful information about the processes, and to change settings ( by modifying the kernel parameters ) on the fly. /proc is stored in memory, unlike other file-systems, which are stored on disk. If you look at the file /proc/mount ( which lists all the mounted file systems, like "mount command), you should see a line in it like:

gerp proc /proc/mounts
/proc /proc proc rw 0 0

/proc is controlled by the kernel and does not have an underlying device. Because it contains mainly state information controlled by the kernel, the most logical place to store the information is in memory controlled by the kernel. Doing a 'ls -l'
on /proc reveals that most of the files are 0 bytes in size; yet when the file is viewed, quite a bit of information is seen. How is this possible ? This happens because the /proc file-system like any other regular file-system registers itself to the Virtual File System layer ( VFS ). However when VFS make calls to it requesting i-nodes for files/directories the /proc file system creates those files/directories from information within the kernel.

Mounting the proc file system:

If already not mounted on your system, proc file system can be mounted on your system by running the following command -

mount -t proc proc /proc

The above command should successfully mount your proc file system. Please read the mount man page for more details.

Viewing the /proc files:

/proc files can be used to access information about the state of the kernel, the attributes of the machine the state of the running processes etc. Most of the files in the /proc directory provide the latest glimpse of a system's physical environment. Although these /proc files are virtual yet they can be viewed using file the file is created on the fly from information within the kernel. Here are some interesting results which i got on my system.

$ ls -l /proc/cpuinfo
-r--r--r-- 1 root root 0 2012-03-06 11:47 /proc/cpuinfo

$ file /proc/cpuinfo
/proc/cpuinfo: empty

processor    : 0
vendor_id    : GenuineIntel
cpu family    : 15
model        : 4
model name    :                   Intel(R) Xeon(TM) CPU 3.40GHz
stepping    : 1
cpu MHz        : 3391.625
cache size    : 1024 KB
physical id    : 0
siblings    : 2
core id        : 0
cpu cores    : 1
fpu        : yes
fpu_exception    : yes
cpuid level    : 5
wp        : yes
flags        : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall lm constant_tsc pni monitor ds_cpl est cid cx16 xtpr
bogomips    : 6792.84
clflush size    : 64
cache_alignment    : 128
address sizes    : 36 bits physical, 48 bits virtual
power management:

processor    : 1
vendor_id    : GenuineIntel
cpu family    : 15
model        : 4
model name    :                   Intel(R) Xeon(TM) CPU 3.40GHz
stepping    : 1
cpu MHz        : 3391.625

ETC..

This is the result for a five-CPU machine. Most of the information above is self-explanatory and gives useful hardware information about the system. Some of the information in /proc files is encoded and various utilities are built that interpret this encoded information and output it in a human readable format. Some of these utilities are: 'top', 'ps', 'apm' etc.

Getting Useful system/kernel information:

The Proc File System can be used to gather useful information about the system and the running kernel. Some of the important files are listed below:

/proc/cpuinfo - information about the CPU ( model, family, cache size etc.)
/proc/meminfo - information about the physical RAM, Swap space etc.
/proc/mounts - list of mounted file system.
/proc/devices - list of available devices
/proc/filesystem - supported file system
/proc/modules - list of loaded modules
/proc/version - Kernel version
/proc/cmdline - Parameters passed to the kernel at the time of starting

There are much more files in /proc than listed above. An alert reader is expected to do a 'more' on every file in /proc directory or read [1]1 for more information about the files present in /proc directory. I suggest to use 'more' and not 'cat' until you know the filesystem a bit because some files (e.g. kcore) can be very large.

Information about running processes:

The /proc file system can be used to retrieve information about any running process. There are couple of numbered sub-directories inside /proc. Each numbered corresponds to a process id (PID). Thus for each running process, there is a sub-directory inside /proc named by its PID. Inside these sub-directories are files that provide important details about the state and environment of a process. Lets try to search for a running process.

$ps -aux | grep mozilla

The above command shows that there is a running process of mozilla with PID ***.

The file "cmdline" contains the command invoked to start the process. The "environ" file contains the environment variables for the process. "status" has status information on the process, including the user (UID) and group (GID) identification for the user executing the process the parent process ID (PPID) that instantiated the PID and the current state of the process such as "Sleeping" or "Running". Each process directory also has a couple of symbolic links. "cwd" is a link to the current working directory for the process ,"exe" to the executable program of the running process, "root" is a link to the directory, which the process, sees as its root directory (usually "/"). The directory "fd" contains links to the file description that the process is using. "cpu" entry appears only on SMP linux kernels. It contains a breakdown of process time by CPU.

/proc/self is an interesting sub-directory that makes it easy for a program to use /proc to find information about its own process. The entry /proc/self is a symbolic link to the /proc directory corresponding to the process accessing the /proc directory.

Interacting with kernel via /proc:

Most of the files in /proc discussed above are read-only. However the /proc file system provides provision of interact with kernel via read-write files inside. Writing to these files can change the state of the kernel and therefore changes to these files should be made with caution. The /proc/sys directory is the one that hosts all the read-write files and thus can be used to change the kernel behaviour.

/porc /sys/kernel - This directory contains information that reflects general kernel behaviour. /proc/sys/kernel/{domainname,hostname} hold the domain-name and hostname for the machine/network. These files can be configured to modify these names.

$hostname
$cat /proc/sys/kernel/domainname
$cat /proc/sys/kernel/hostname
$echo "new-machinename" > /proc/sys/kernel/hostname
$hostname

Thus by modifying the file inside /proc file system. we are able to modify the hostname. Lots of other configurable files exists inside /proc/sys/kernel. Again its impossible to list down every file here so readers are expected to go through this directory in detail.
Another configurable directory is /proc/sys/net. Files inside this directory can be modified to change the networking properties of the machine/network. E.g. By simply modifying a file, you can hide your machine in the network.

$echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_all

This will hide your machine in the network as it disables answers to icmp_echos. The host will not respond to ping queries from other hosts.

$ ping machiname.domainname.com

To trun it back to default behaviour, do
$echo 0> /proc/sys/net/ipv4/icmp_echo_ignore_all

There are lots of other sub-directories in /proc/sys which can be configured to change the kernel properties. See [1],[2] for detailed information.

Conclusion:

The /proc File System provides a file-based interface to the linux internals. It assists in determining the state and configuration of various devices and processes on system. Understanding and applied knowledge of this file-system is therefore the key to making the most out of your linux system.

vi editor

2012-03-06T14:47:00.000+05:30

VI Editor

What is vi?

The default editor that comes with the UNIX operating system is called vi ( visual editor ). [Alternate editors for UNIX environments include pico and emacs, a product of GNU.]
The UNIX vi editor is a full screen editor and has two modes of operation:

command mode commands which cause action to be taken on the file, and
Insert mode in which entered text is inserted into the file.

In the command mode, every character typed is a command that does something to the text file being edited; a character typed in the command mode may even cause the vi editor to enter the insert mode. In the insert mode, every character typed is added to the text in the file; pressing the (Escape) key turns off the Insert mode.

While there are a number of vi commands just a handful of these is usually sufficient for beginning vi users. To assist such users, this web page contains a sampling of basic vi commands. The most basic and useful commands are marked with an asterisk (* or star) in the tables below. With practice these commands should become automatic.
NOTE: bot UNIX and vi are case-sensitive. Be suer not to use capital letter in place of a lower-case letter; the results will not be what you expect.

To get into and out of vi :

To start vi
To use vi on the type in vi filename. If the file named filename exists, then the first page ( or screen ) of the file will be displayed; if the does not exist, then an empty file and screen are created into which you may enter text.

*	Vi filename	Edit filename starrting at line 1
	Vi -r filename	Recover filename that was being edited when system crashed

To Exit vi
Usually the new or modified file is saved when you leave vi. However it is also possible to quit vi without saving the file.
NOTE: The course moves to bottom of screen whenever a colon(:) is typed. This type of command is completed by hitting the (or ) key.

Quit vi, writing out modified file to file named in original invocation

A common occurrence in text editing is to replace one word or phase by another. To locate instances of particular sets of characters ( or strings ) use the following commands.

/string	Search forward for occurrence of string in text
?string	Search backward for occurrence of string in text
n	Move to next occurrence of search string
N	Move to next occurrence of search string on opposite direction

Determining Line Number:
Being able to determine the line number of the current line or the total number of lines in the file being edited is sometimes useful.

: .=	Returns line number of current line at bottom of screen
:=	Returns the total number of lines at bottom of screen
^g	Provides the current line number, along with the total number of lines, in the file at the bottom of the screen

Saving and Reading Files:
These commands permit you to input and output files other than the named file with which you are currently working.

:r filename	Read file named filename and insert after current line ( the line with cursor)
:w	Write current contents to file named in original vi call
:w newfile	Write current contents to a new file named newfile
:12, 35w smallfile	Write the contents of the lines numbered 12 through 35 to a new file named smallfile
:w! prevfile	Write current contents over a pre-existing file named prevfile

^f	Move forward one screen
^b	Move backward one screen
^d	Move down (forward) one half screen
^u	Move up (back) one half screen
^l	Redraws the screen
^r	Redraws the screen, removing deleted lines

Adding, Changing and Deleting Text :
Unlike PC editors you cannot replace or delete text by highlighting it with the mouse. Instead use the commands in the following tables.
Perhaps the most important command is the one that allows you to back up and undo your last action. Unfortunately this command acts like a toggle undoing and redoing your most recent action. You cannot go back more than one step.

Undo whatever you just did; a simple toggle

The main purpose of an editor is to create, add, or modify text for a file.
Inserting or Adding Text:
The following commands allow you to insert and add text. Each of these commands puts the vi editor into insert mode; thus the key must be pressed to terminate the entry of text and to put the vi editor back into command mode.

*	i	Insert text before cursor, until hit
	I	Insert text at beginning of current line, until hit
*	a	Append text after curson, until hit
	A	Append text to end of current line, until hit
*	o	Open and put text in a new line below current line until hit
*	O	Open and put text in a new line above current line, until hit

Changing Text:
The following commands allow you to modify text.

*	r	Replace single character under cursor (no needed)
	R	Replace characters, starting with current cursor position, until hit
	cw	Change the current word with new text, starting with the character under cursor, until hit
	cNw	Change N words beginning with character under cursor, until ,ESC> hit; e.g. C5w changes 5 word
	C	Change (replace) the characters in the current line, until hit
	cc	Change (replace) the entire current line, stopping when is hit
	Ncc OR cNc	Change (replace) the next N lines, starting with the current line, stopping when is hit

Deleting Text:
The following commands allow you to delete text.

*	x	Delete single character under cursor
	Nx	Delete N character, starting with character under cursor
	dw	Delete the single word beginning with character under cursor
	dNw	Delete N words beginning with character under cursor; e.g. d%w delete 5 words
	D	Delete the remainder of the line starting with current cursor position
*	dd	Delete entrie current line
	Ndd or dNd	Delete N lines, beginning with the current line; e.g. 5Dd delete 5 lines

Cutting and Pasting Text:
The following commands allow you to copy and paste text.

yy	Copy (yank, cut) the current line into the buffer
Nyy or yNy	Copy (yank,cut) the next N lines, including the current line, into the buffer
p	Put (paste) the line(s) in the buffer into the text after the current line

Other Commands:
Searching Text:

	:wq	Quit vi, writing out modified file to file named in original invocation
	:q	Quit (or exit) vi
*	:q!	Quit vi even though latest changes have not been saved for this vi call

Moving the cursor:
Unlike many of the PC and MacIntosh editors, the mouse does not move the cursor within the vi editor screen (or window). You must use the key commands listed below. On some UNIX platforms, the arrow keys may be used as well; however since vi was designed with the Qwerty keyboard ( containing no arrow keys) in mind, the arrow keys sometimes produce strange effects in vi and should be avoided.
If you go back and forth between a PC environment and a UNIX environment, you may find that this dissimilarity in methods for cursor movement is the most frustrating difference between the two.
In the table below the symbol ^ before a letter means that the key should be held down while the letter key is pressed.

*	J or [or down-arrow]	Move cursor down one line
*	K [or up-arrow]	Move cursor up one line
*	H or [ or left-arrow]	Move cursor left one character
*	L or [ or right-arrow]	Move cursor right one character
*	0 (zero)	Move cursor to start of current line ( the one with the cursor)
*	$	Move cursor to end of current line
	w	Move cursor to beginning of next word
	b	Move cursor back to beginning of preceding word
	:0 or lG	Move cursor to first line in file
	:n or nG	Move cursor to line n
	:$ or G	Move cursor to last line in file

Screen Manipulation:
The following commands allow the vi editor screen ( or windows ) to move up or down several lines and to be refreshed.

File System Commands

2012-03-05T18:53:00.000+05:30

File System Commands

Linux look at everything as a file. Linux file system will have tens of thousands of files. If you write a program you add one more file to the system. When you compile it you are adding at least two more.

Linux file is a storehouse of information. It is simply a sequence of charaters. linux places no restriction on the structure of the file. A file contains exactly those bytes that you out in to it, be it a source program executable code or anything else. It neither contains it's own size not it's attributes. It doesn't contain it's own name.

Although everything is treated as a file by linux it's still divided files into various categories:

Ordinary files, device files, directory files etc.

Commands:

pwd: Checking current directory:

When you log in you are placed in a specific directory of the file system. This directory is known as your current directory. At any time you should be able to know what your current directory. At any time, you should be able to know what your current directory is. For this we have to use the "pwd" command.

$pwd
/usr/ben

cd: changing directories:

We can move around in the file system using cd command. It changes the current directory to the directory specified as the argument. For example:

$pwd
/user/username
$cd progs
$pwd
/user/username/progs

The command cd progs means change your subdirectory to progs under the current directory. If we use absolute pathname that also the effect will be the same. You can use like this also

cd /user/username/progs

If we want to switch to the /bin directory where most of the Unix/Linux commands are kept in that case we have to use the absolute pathname.
If we use cd without ant argument then it reverts to the home directory.

mkdir: Making Directories:

We can create directories with mkdir command. This command is followed by the named of the directories to create. If we want to make the directory by the name patch.

$mkdir patch

We can create number of sub directories in a single shot.

$mkdir one two three

Unix/Linux systems lets we create directory chain with just one command. For example:

$mkdir foo foo/one foo/two

This command creates three subdirectories- foo & two subdirectories under foo.
But we can't enter like this-

$mkdir foo/one foo/two foo

This command failed to create two subdirectories one & two but still creates foo
directory.

rmdir: Removing Directories:

We can remove directories with rmdir command. For example:

$rmdir patch
Like mkdir, rmdir can also delete more than one directory in a single shot. For example:

$rmdir one two tree
Also the tree directories & subdirectories that we just prepared using mkdir can be removed by using rmdir with reverse set of arguments.

$ rmdir foo/one foo/two foo

But we can't enter like this.
$rmdir foo foo/one foo/two

In this case, rmdir will silently delete the lowest levels of directories one & two. You should remember the following rules while deleting the directories.

"you can't delete the directory unless it is empty. In this case foo directory can't be removed because of the existence of the directories one & two.

You can't remove a subdirectory unless you are placed in a directory, which is hierarchically above the one you have chosen to remove.

To understand this look at the following example.

$cd progs
$pwd
/user/useraname/progs
$rmdir progs
rmdir:progs:Directory does not exit.

To remove this directory we must position ourselves in the directory above progs that is username & remove it from there.

$cd /user/username
$pwd
/user/username
$rmdir progs

The mkdir and rmdir commands work with only those directories, which are owned by the user.

ls: Listing Files:

This command is used to list all the files in the current directory.

$ls

We can see here there is a complete list of filenames in the current directory. Arranged in ASCII collating sequence with one filename in each line.
If you want a particular file then just use ls with particular filename.

$ls patch
patch

-x Option:Output In Multiple columns:
When we have several files then it is better to display the filename in multiple columns. So we need the -x option to produce the multi-columnar output.
-F option: Identifying Directories & Executables:
With the help of ls command we got only the filenames, but we didn't know how many of them are directories & executable files. To get this -F option should be used.

$ls -F

Note that the two symbols that tag some of the filenames the * indicates the file containing the executable code & the / refers to a directory.

-a Option:Showing Hidden Files:

ls command doesn't show all the files in a directory. Some of files are hidden files in every directory. This option lists all the files even hidden files also.

All these files beginning with a '.' are normally not listed out only with ls.

-r Option: Reversing the sort order:

We can reverse the order of the presentation of the list with the -r option. The sorting is done in the reverse ASCII collating order.

$ls -r

The ls command will work differently if we give the two directory names with it. $ls directory1 directory2
Here is the list of important option:

Options	Description
-x	Display multi-columnar output
-r	Sorts files in reverse order
-R	Recursive listing of all files in subdirectories
-F	Makes executables with * & directories with /
-a	Shows all files including hidden ones
-i	Shows inode number of files
-l	Long listing showing seven attributes of flies
-d	Force listing of directories
-t	Sorts files by modification time
-u	Sorts files by access time

cat : Displaying and Creating Files:
cat command is generally used to display the contents of a file.
$cat filename
cat command also accepts more than one filenames
$cat file1 file2
The contents of second file are shown immediately after the contents of first file. cat is normally used to display the text files only.
Using cat to create file:
cat is used for creating files. Look at the following examples:
$cat>one
This command shows the inserting of data into the files. ( Ctrl -d)
$ prompt returns
When we terminate the command line after pressing the enter key the prompt vanishes & now waits for input the user side. Finally press the control-d to signify the end of data input.

cp: Copying of files:
Copy the contents of one file to another with the cp command.
syntax
cp [options] old_filename new_filename
you now have two copies of the file, each with identical contents. They are completely independent of each other and you can edit and modify either as needed. They each have their own inode, data blocks and directory table entries.

We can also copy files to another directory. For example
cp one progs/two
cp can also be used to copy more than one file in a single shot. In that case the last filename must be a directory. For example : to copy files one, two, tree to the progs directory we have to write.
$cp one two tree progs
To work this command it is necessary that progs directory should be there.
you can also use * metacharacter if the names having same starting characters. For example: if filename are page1, page2, page3.
cp page* progs

Common Options
-i : interactive ( prompt and wait for confirmation before proceeding)
$cp -i one two
cp:overwrite two?y/n
-r: recursively copy a directory
It is possible to copy entire directory structure with this option. For example the following command copies all files & subdirectories from progs to newprogs.
cp -r progs newprogs

rm: Deleting files:
Remove a file with the rm, remove command.
syntax
rm [option] filename
common options
-i : interactive ( prompt and wait for confirmation before proceeding )
-r : recursively remove a directory, first removing the files and
      subdirectories beneath it.
-f : don't prompt for confirmation (overrides -i)

Examples:
$rm old_filename
A listing of the directory will now show that the file no longer exists. Actually all you've done is to remove the directory table entry and mark the inode as unused. The file contents are still on the disk, but the system now has no way of identifying those data blocks with a file name. There is no command to "unremove" a file that have been removed in this way. For this reason many novice users alias their remove command to be "rm -i" where the -i option prompts them to answer yes or no before the file is removed.
rm dosen't normally remove directory but removes the files from it. You can remove two files from foo directory without having to "cd" to it.
$rm foo/one/ foo/two
sometimes it is required to delete all the files of directory then we can use the * metacharacter which represents all files. For example:
$rm *

mv: Renaming Files:
Rename a file with the move command, mv.
Syntax:
mv [option] old_filename new_filename

Common Options:
-i interactive (prompt and wait for confirmation before preceeding)
-f don't prompt even when copying over and existing target file ( overrides -i )
Example:
$mv old_filename new_filename
You now have a file called new_filename and the file old_filename is gone. Actually all you've done is to update the directory table entry to give the file a new name. The contents of the file remain where they were.
mv can also be used to rename a directory.

more:Paging Output:
If the file too large to display it's contents on screen, then the contents will scroll off the screen when we view it with cat. So a pager is required more allows the user to view a file one screen at a time. To view the contents of a file page1 use the following command with the filename.
$more page1
You will see the contents on the screen one page at a time. At the bottom of the screen, you will see the filename with the percentage of file content that has been viewed.
more command also contains some internal commands-
q- this command is used to exit more.
f- to scroll forward one screen.
b- to scroll backward one screen.
to move even slowly only one line at a time use, j key for scrolling.
forward and k for scrolling backward.
we can use more with multiple filenames.
more page1 page2 page3
you will first see the contents of the first file preceded by it's name after that the message "page1:ENDS(next file: page2)" and then the contents of the next file. In this way it display the contents of all the files. In between we can switch to previous or next files also using :n or :p for next and previous voyage.

lp (Line Printing): Printing A File:
Users are not allowed to directly access the printer. But users can spool ( or line up) a job with others in a print queue. With spooling one can orderly print the jobs relieve the user from the necessity of administering the usage of print resources. The spooling facility is provided by the lp command. Take a look at following example:
$lp page1
request id is pr1-100(1 file )
This command will print a single copy of first page. This command also gives the request id. It is the combination of printer name & job number.
If there are more than one printer in a system, we have to use the -d option with the printer name if the printer name is dotmatrix.
$lp -ddotmatrix page1
The another option we can use with lp is -t ( title ) followed by the title string. this command prints the title on the first page.
$lp -t "first page" page1
We can cancel our jobs with cancel command which requires the request id of the job as an argument.
$ cancel pr1-100

file: To know the file types:
There are three of files. i.e. ordinary files directory files & device files. A regular file may contain simple text a C program or executable file. This file command is used to determine the type of file.
$file filename.lst
filename.lst: English text
This command you can use with more filename also. We can apply this command to all the files in the progs directory. Just look at the following example ( * to indicate all the files )
$file /proc/*

wc: Line, Words and Character Count:
This command counts lines, words and characters depending on the options used. It takes one or more file name as an argument. Before you use wc command take a look at the following example

$create a file type some lines.
$ cat > filename
$wc filename
This command offers three option to make specific count. This -l counts only number of lines, -w counts number of words and -c counts number of characters.
$wc -l filename
$wc -w filename
$wc -c filename
we can use this command with multiple file names, wc produces a separate line for each file.
$ wc file1 file2 file3

split: Splitting a file into multiple files:

Some file are so large that some times we found difficulties in editing them. So there's a need to split them. The split command breaks up its input into several equi-line segments and all these segments are created as separate file in the current directory. Split by default break up a file into 1000 line pieces.
$split file1
This command creates a group of files xaa, xab, xac like this up to xzz. If the file is not large enough to occupy 1000 line you can override this default figure of 1000 by specifying the size.
$split -101 filename
Each file will contain 101 lines.

cmp: Comparing Two files:
Some times two files are exactly identical to each other, in such cases you can delete one of them. There are three commands to do this comparison one of them is cmp command. this command requires two file names as an argument.
$cmp file1 file2
This command compares the two files byte by byte and location of the first mismatch gives on the screen. The -l option gives a detailed list of byte number and differing bytes in octal for each character, that differs in both files.
$cmp -l file1 file2
If the two files are identical the cmp does not display many message but it simple returns the $ prompt.
diff: Differences in files:
The diff command compares two files, directories, etc and reports all differences between the two. It deals only with ASCII files. It's output format is designed to report the changes necessary to convert the first file into the second.
Syntax:
diff [option] file1 file2
Common Options
-b ignore trailing blanks
-i ignore the case of letters
-w ignore and characters
-e produce and output formated for use with the editor, ed
-r apply diff recursively through common sub-directories
Examples:
For the file1 and file2 files, the difference between them:
Note that the output lists the differences as well as in which file the difference exists.
Lines in the first file are preceded by "<", and those in the second file are preceded by ">".

File Permissions:
Each file, directory and executable has permission set for who can rad, write, and/or execute it. To find the permissions assigned to a file, the ls command with the -l option should be used. Also using the -g option with "ls -l" will help when it is necessary to know the group for which the permissions are set ( BSD only ).
When using the "ls -lg" command on a file ( ls -l on sysV), the output will appear as follows.
-rwx-r-x--- user unixgroup size month nn hh:mm filename
The are above designated by letters and dashes ( -rwx-r-x---) is the area showing the file type and permissions. Therefore, a permission string for example of -rwx-r-x--- allows the use ( owner ) of the read, write and execute it; those in the unixgroup of the file can rad and execute it; others cannot access it at all.

Chmod - Change File Permissions:
The command to change permissions on an item ( file, directory, etc) is chmod ( changes mode). The syntax involves using the command with three digits ( representing the user ( owner, u) permission, the group (g) permissions, and other (o) user's permissions) followed by the argument (which may be a file name or list of files and directories). Or by using symbolic representation for the permissions and who they apply to.
Each of the permission types is represented by either a numeric equivalent:
read=4, write=2, execute=1
or single letter:
read-=r, write=w, execute=x
A permission of 4 or r would specify read permissions. If the permission desired are read and write, the 4 (representing rad) and the 2 (representing write) are added together to make a permission of 6. Therefore, a permission setting of 6 would allow read and write permissions.
Alternatively you could use symbolic notation which uses the one letter representation for who and for the permissions and an operator, where the operator can be:
+ add permissions
- remove permissions
= set permissions
So to set read and write the owner we could use "u=rw" in symbolic notation.
Syntax:
$ chmod nnn [argument list] numeric mode
$ chmod [ who]op[prem] [argument list] symbolic mode
Where nnn are the three numbers representing user, group and other permissions, who is any u, g, o or a (all) and perm is any of r, w, x . In symbolic natation you can separate permission specifications by commas as shown in the example below.
Common Options:
-f force (no error message is generated if the change is unsucessful)
-R recursively descend through the directory structure and change the modes.

Example:
If the permission desired for file1 is user: read, write, execute, group: read, execute, other: rad, execute the command to use would be
$ chmod 755 file2 or chmod u=rwx,go=rx file1
Reminder: When giving permissions to group and other to use a file, it is necessary to allow a least execute permission to the directories for the path in which the file is located. The easiest way to do this is to be in the directory for which permissions need to be granted.
chmod 7111. or chmod u=rw,+x. or chmod u=rwx.go=x.
where the dot (.) indicates this directory.

Shell
Shell is command interpreter that execute commands. A Unix shell is both a command interpreter, which provides the user interface to the rich set of unix utilities, and a programming language allowing these utilities to be combined. Files containing commands can be created and become commands themselves. These new commands have the same status as system command in directories like '/bin', allowing users or groups to establish custom environments.
A shell allows execution of unix command both synchronously and asynchronously. The shell waits for synchronous commands to complete before accepting more input; asynchronous commands continue to execute in parallel with the shell while it reads and executes additional commands. The redirection construct permit fine-grained control of the input and output of those commands and the shell allows control over the contents of their environment. Unix shells also provide a small set of built in commands ( builtins ) implementing functionality impossible ( e.g. cd, break, continue and exec ), or inconvenient ( history, getopts, kill or pwd for example ) to obtain via separate utilities. Shells may be used interactively or non-interactively they accept input typed from the keyboard or from a file.
While executing commands is essential most of the power ( and complexity ) of shells is due to their embedded programming languages. Like any high-level language, the shell provides variables flow control constructs, quoting and functions.
Shells have begun offering features geared specifically for interactive use rather than to augment the programming language. These interactive features include job control command line editing history and aliases.
Shell Operations:
The following is a brief description of the shell's operation when it reads and executes a command. Basically the shell does the following:
Reads it input from a file, from a string supplied as an argument to the '-c' invocation or from the user's terminal.
Breaks the input into words and operators, obeying the quoting rules. These tokens are separated by metacharacters. Alias expansion is performed by this step.
Parses the tokens into simple and compound commands.
Performs the various shell expansions, breaking the expanded tokens into lists of filenames and commands and arguments.
Performs any necessary redirections and removes the redirection operators and their operands from the argument list.
Executes the command.
Optionally waits for the command to complete and collects its exit status.

comments:
In a non-interactive shell or an interactive shell in which the interactive_comments option to the shops built in is enabled a word beginning with '#' causes that word and all remaining characters on that line to be ignored. An interactive shell without the interactive_comments option enable does not allow comments. The interactive_comments option is on by default in interactive shells.

Pipelines:
A pipeline is a sequence of simple commands separated by '|'. The formate for a pipeline is -
[time [-p]] [!] command1 [|command2..]
The output of each command in the pipeline is connected to the input of the next command. That is each command reads the previous command's output.

Pattern Matching : Wild cards:
Up to this point we used certain commands with more than one filename (e.g., page1 page2, page3) as arguments. Often you may require to enter a number of such filenames in the command line. To illustrate this look at the following examples:
$ls -l file1 file2 file3
Each filename has a common string viz., page. But this command line requires lot of typing work & doesn't look good. Fortunately shell offers solution to this.
The * And ?
this * is known as metacharacter. this character matches any number of characters. When this character is appended to the string page the pattern page * expands in to all files in which first four characters constitute to string page. The previous command line can now be shortened with this sequence.
$ ls -l file*
Now when shell encounters the above command line it looks for metacharacters & identifies the * immediately. It then matches all the files in the current directory with the pattern page start and replace the pattern with the list that matches the pattern. It then reconstructs the command line as below & passes it to the kernel for execution.
$ls -l file1 file2 file3
The next character is ? , which matches a single character. When used with the same string page (page?) the shell matches all five character filenames beginning with page. Placing another? at the end of this string creates the pattern page?? where page is followed by two characters. Look at the following example.
$ls -x file?

Pattern Matching
Any character that appears in a pattern other than the special pattern characters described below, matches itself. The NULL character may not occur in a pattern. The special pattern characters must be quoted if they are to be matched literally.
The special pattern characters have the following meanings:
* Matches any string including the null string.
? Matches any single character.
[...] Matches any one of the enclosed characters. A pair of characters separated by a minus sign denotes a range; any character lexically between those two character, inclusive is matched. If the first character following the `['is a ` !' or a `^' then any character not enclosed is matched. A `_' may be matched by including it as the first or last character in the set. A `}' may be matched by including it as the first character in the set. Within `[' and `]' , character classes can be specified using the syntax [:class:], where class is one of the following classes defined in the POSIX.2 standard:
alnum alpha ascii blank cntrl digit graph lower print punct space upper sdigit
A character class matches any character belonging to that class. Within `[' and `]', an equivalence class can be specified using the syntax [=c=], which matches all characters with the same collation weight ( as defined by the current locale ) as the character c. Within `[' and `]', the syntax [.symbol.] matches the collating symbol symbol.
If the extglob shell option is enable using the shopt built in, several extended pattern-matching operators are recognized. In the following description, a pattern-list is a list of one or more patterns separated by a `|'. Composite patterns may be formed using one or more of the following sub-patterns:
? ( pattern-list)
         Matches zero or one occurrence of the given patterns.
* ( pattern-list)
Matches zero or more occurrences of the given patterns.
+ ( pattern-list)
Matches one or more occurrences of the given patterns.
@ ( pattern-list)
       Matches exactly one of the given patterns.
! ( pattern-list)
   Matches anything except one of the given patterns.

When Wild - Cards lose their meaning:
The metacharacters * and ? lose their meaning when used inside the class & are matched literally. Similarly - & ! also lose their significance when placed outside the class. Additionally ! loses it's meaning when placed anywhere but at the beginning of the class. The - loses it's meaning if it is not bounded properly on either side by a single character.
Matching the Dot:
The * doesn't match all the files beginning with a . (dot) or the / of a pathename. If you want to list all the hidden files in your directory having at least 3 characters after the dot, then the dot or the must be matched explicitly.
$ls -x .???*

When using rm with *:
We use these metacharacter to speed up our interaction with the system but there are great risks involved if you are not alert. When using shell metacharacters especially the *, you could be totally at sea if instead of typing
$rm file*
Which removes all file. You inadvertently introduces space.
$rm file * ( space between page and * )
Even if there is not file named file in the current directory, and you get an error message to indicate that the command will still removed all files in this directory because of singular existence of *. This happens because shell rightly treats the * as a separate argument.
Escaping: The Backslash (\):
It is generally accepted principle that file names should not contain the shell meta characters. What happens if we do that imagine a file named page* created with the >.
Symbol:
$>file*    # you can create any empty file like this

How do we remove this file without deleting other files. ( If we have other files named file1, file2, file3). the shell uses another characters \(Backslash), to remove the special meaning of any metacharacter placed after it. Here the shell has to be told that the asterisk has to treated & matched literally, instead of being interpreted as metacharacter use the \ before * to solve the problem.
$ ls -x file\*
file*
$ rm file\*
Escaping The < ENTER> Key:
When you enter a long chain of commands you can split the command line by hitting enter key. But only after the \ escapes this key.
$wc -l file1 \ ( Enter)
> file2 file3 ( Press Enter )

Quoting:
What happens when we enter a shell metacharacter with echo command as below:
$echo *
showing files and directories
You simply see list of all files in the current directory. Why that happens? The shell uses the * meta character to match the files in the current directory. All files matched so you see all of them in the output. Suppose you intend to literally echo a * without permitting the shell to interfere. Escaping with a \, solves the problem.
$echo \*
There is another solution. When the argument to a command is enclosed in quotes the meaning of all special characters are turn off.
$echo '*' ( you can use double quotes also )

Quoting Preserves Spaces:
Whenever a shell finds contiguous spaces & tabs in the command line, it compresses them to a single space. Look at the following example:
$echo write one or two lines with so many space.
The above arguments to echo could have been preserved by escaping the space character, whenever it occurs at least twice.
$ echo dflfjdasl\ \ \sdafsda\ \ \sdfsad\ \    \sdfsad\.
In this situation quoting is recommended.
$echo "sdfklsajlfjsadl;"

grep: Searching For A Pattern:
grep is one of the most useful unix filter. It scans the file for a specific occurrence of a pattern, and displays the selected pattern the filenames where that pattern occurs or the line number in which they found. The syntax for it is as follows- grep option pattern filename (s)
Look at the following example
$ps -aux | gerp firefox
grep when unable to find the required pattern then it silently returns the prompt. Take a look at this -
$ grep production record1.lst
$-    #No production person found
It is generally safe to quote the pattern though always it is not required. Quoting is essential if the search string consist of more than one word. Try the following example -
$grep baiju damoder record.lst
gerp:can't open damodar
gerp interprets damodar as a filename and so unable to open that file. but still searches the record1.lst and gives the result. To correct this problem you quote the pattern just like -
$ grep 'jiten' record1.lst
When we use grep with a series of string it interprets the first arguments as the pattern & the rest as filenames. It then displays along with the output.
$grep manager record1.lst record2.lst
grep options:

Option	Significance
-c	Displays count of number of occurances
-l	Displays list of filename only
-n	Display line number along with lines
-v	Displays all but lines matching expressions
-i	Ignores care for matching
-h	Omits filenamewhrn handling multiple files
-n	Display line & n lines above & below

User and Group Management

2012-02-29T18:01:00.000+05:30

User and Group Management

Description:

Managing user accounts in linux is of paramount importance as users need an ID just to login to the system. Create, Delete and Change user attributes.

Introduction:

Linux being a multi-user, multitasking operating system, needs every user to possess a user name and a password. So to efficiently use linux we first need to know the process of creation of users and using the created users to logon and logout of the system.

We summaries a few points regarding user accounts.

Linux operating system is case sensitive. This imposes that we use commands in the lower case to get our work done. Command typed upper-case will throw errors.

Every on a Linux system needs a user account.

Every account has right ans privileges that very depending on the command and the directory.

Linux users are organized into groups.

In RHEL user accounts are organized in the '/etc/passwd' file.

Their passwords are made more secure by the use of the '/etc/shadow' file.

When creating a new account the default parameters are configured in the '/etc/login.defs' file.

Configuration files are stored in another directory from where the files are copied to the user's home directory while the user is created.

Introduction to files that relate to the users of a system:

/etc/passwd

Linux users are classified into three types

Administrative (root)
Regular
Service

The administrative root account is automatically created when you install linux which has administrative privileges for all services on your linux box.

Regular users have the necessary privileges to perform standard task on linux computer. They can access programs such as word processors, databases and web browsers. They can store files in their home directories only.

Services such as Apache, ftp, Squid, nail, games, audio etc. have their own individual service accounts.

each column in the '/etc/passwd' file is delimited by a colon(:)

Column	Function	Comment
1	Username	Login name of the account
2	Password	If this field contains an X, the encrypted password is stored in /etc/shadow
3	UserID	A numeric ID for the usr. Assigned by the OS
4	GroupID	A numeric ID for the default group of the user. Assigned by the OS
5	Extra Information	Commonly used for the user's ral name. Can be any comment on the account
6	Home directory	The path to the user's home directory
7	Defaulty shell	The shell the user sees after logging in

/etc/shadow

This is the file that holds the password information of the users of the machine.

It is a read-only file for the root and no permissions are afforded for anyone else. Hence it is more secure.

If you use standard command to create new users, basic information is also added to this file based on the defaults in the '/etc/login.def

Column	Function	Comment
1	Username	Login name
2	Password	The encrypted password. Blank if the user has no password. A * signifies a password has not been defined. If the useris disable from logging in to the system an ! Is displayed.
3	Number of days	Last time the password was chagned in days after january 1,1970
4	Minimum password life	You can't change the password for at least this amount of time in days.
5	Maximum password life	You have to change the password after this period of time in days
6	Warning period	You get a warning this name days before your password expires
7	Disable account	If you don't use your account this many days after your password expires, you can't log in
8	Account expiration	If you don't use your account by this date, you won't be able to log in. Maybe in yyyy-mm-dd format or in number of days after january 1,1970

/etc/skel

Users have a default set of configuration files and directories.

The default list of these files is located in the '/etc/skel' directory.

you can see the files by listing the hidden contents of the skel directory.

All new users will get a copy of these files in their home directories.

Files	Purpose
.bashrc	The basic bash cofiguration file. May include a reference to the general /etc/bashrc
.bash_logout	A file executed when you exit a bash shell. Can include commands appropriate for this purpose, such as clearing your screen
.bash_profile	Configures the bash start up environment. Appropriate place to add environment variables or to modify the directories in your PATH
.gnome*	Servral directories that include start up setting for the GNOME desktop environment. For example, details of desktop icons such as Trash are stored in .gnome-desktop/Trash
.gtkrc	Adds the bluecurve theme for the default Red Hat GUI
.kde	A dirctory that includes auto start setting for the K Desktop environment. Not copied to the users home directories if you haven't installed KDE in the computer.

/etc/login.defs

When you create a new user the basic parameters come from the /etc/login.defs configuration file.

The version included with RedHat Linux includes settings for

Email directories
Password directories
UserID numbers
GroupID numbers
Creating a home directory

Adding Users - Creating and management of user account :

Login/Logout, Shutting down, Restarting a System and using commands to add users

To logon to the system you should enter username and password

login: username

password: **********

To create a user

#useradd username ( Read man page for more controlled user creation )

#man useradd

To set the password for the newly created user

#passwd username

To log off the system and enter as a new user

#exit

To shut-down a system

#init 0

#shutdown -h now

#poweroff

To restart a system

#init 6

#shutdown -r now

#reboot

Editing the /etc/passwd file directly:

Open the /etc/passwd file for editing using a text editor.

# vim /etc/passwd

Start a new line. the easiest way to do this is by copying the applicable information from a current user.

Substitute the information of your choice to create the new user.

For example change the user name as testuser, UID as 1010, GID as 1010, full name as "This is a test user" ( less the quotes), /home/testuser as the home directory.

Save and Exit.

Open the /etc/shadow file for editing using a test editor.

# vim /etc/shadow

Create a new line by copying the applicable information from a current user.

Change the group name as testuser and GID as 1010.

Save and exit.

Set up your new user's home directory.

#mkdir -p /home/testuser

Give the new user access to his home directory.

# chown testuser:testuser /home/testuser

Assign a new password with passwd command

# su -testuser

Copy the basic initialization files which are normally stored in the /etc/skel directory.

#cp -r /etc/skel/ /home/testuser

#cd /home/testuser

#mv /etc/skel/* . ---------------------------> (ignore error message)

#mv /etc/skel/.* .

#rmdir skel

Change the Ownership of the files and directories copied to the home directory of the user.

#chown testuser:testuser /home/testuser /home/testuser

Logout from the user's account.

Assuming you're using the default shadow password suite, run the pwconv and grpconv commands.

Deleting user account by deleting entries in the files:

Delete the user's entry from the /etc/passed file.
Delete the user's entry from the /etc/group file.
Delete the user's entry from the /etc/shadow file.
Delete the user's entry from the /etc/gshadow file.
Delete the user's home directory after saving the files you need.

Commands:

Useradd -u 1010 -g 1010 -s /bin/bash -d /home/testuser -m testuser

#useradd username

#useradd -u UID username

#useradd -g GID username

#useradd -G username

#useradd -c username

#useradd -s username

#useradd -e username

#useradd -d username

#useradd -m username {to create the home directory if it does not exist}

Usermod -l -L -U:

usermod -l {to change the user login name}

usermod -L { to lock a user account}

usermod -U {to unlock user accounts}

change:

chage -m { sets minimum life of password to days}

chage -M { sets maximum life of password to days}

chage -I {sets the number of days that an account can be

inactive before it is locked}

chage -W {sets an advance warning in says of an upcaming

mandatory password change}

chage -l {list the current user password information. can be

used by regular users on their own accounts}

The Shadow password Suite:

The Shadow Password Suite features all of the commands related to managing Linux users and groups.

By default RedHat Linux uses this suite to provide additional security through encrypting passwords in the /etc/shadow and the /etc/gshadow files.

These files require commands to convert passwords to and from the companion /etc/passwd and the /etc/group configuration files.

These encrypted password files have more restrictive permissions than /etc/passwd or /etc/group; only the root user is allowed to only view these files and they are not writable by default.

Converting User Passwords:

Two commands are associated with converting user password in the shadow password suite.

pwconv

pwunconv

pwconv:

Converts an existing /etc/passwd file. Passwords that currently exist in the /etc/passwd are replaced by a "x" the encrypted password, username, and the other relevant information are transferred to the /etc/shadow file.

If you've recently added new users by editing the /etc/passwd file in a text editor you must run this command again to convert the passwords associated with any new users.

pwunconv:

Password are transferred back to the /etc/passwd, and the /etc/shadow file is deleted.

Be careful as this also deletes any password aging information.

/etc/group:

Every linux user is assigned to a group.
By default every user gets their own private group.
This file has four columns as follows

Column	Function	Comment
1	Group name	By default red hat users are members of a group with their username
2	Password	If you see and 'x' in this column, see /etc/gshadow for the actual encrypted password
3	GroupID	By default redhat users have a GID same as their UID
4	Members	Includes the usrnames of others that are the members of the group

/etc/gshadow:

The RHEl /etc/gshadow configuration file for the group is analogous to the /etc/shadow file for users.
It specifies an encrypted password for applicable group, as well as administrators with privileges for a specific group.
This file has four columns as follows

Column	Function	Comment
1	Group name	You can create additional groups.
2	Password	The encrypted group password, added with the gpasswd command.
3	Group Administrator	The user is allowed to manage users in that group.
4	Group Members	Includes the usernames that are the members of the same group.

Group Commands:

#groupadd -g GID
#groupadd -n
#groupdel
#groups < username> {displays the group memberships that the

user has}

#id { to get ID information}

RedHat Package Management

2012-02-28T15:07:00.000+05:30

Red Hat Package Management

Description :

Every user of a linux system needs to install or remove software in his system. There are a few methods available by which one can install software into Red Hat Linux. One method is to user the source tarballs to install the packages into linux and the second method is to user per-compiled binaries into the system. These are usually called as RPM and in Debian it is call DPKG packages.
Red Hat package Management utility to install and remove packages from a Linux system.

Introduction:

Generally a package's name will be in the following format.

packagename.version.release.architecture.rpm

Eg. firefox-4.0rc2.tar.bz2,firefox.9.0.0.1-0.1.mga1.x86_64.rpm

Redhat Linux includes a tool name rpm to administer the software packages. Using rpm command you can:

Installing Packages
Upgrading Packages
Removing packages
Querying Packages
Removing Packages

Command Syntax: root@linux:~#rpm -I [option] package

Package is the complete name of the package to be installed. The options refine the installation process. The options are explained below.

-v    Turn on verbosity. Shows some useful information during the
                   installation.
-h               Print up to 50 hash marks (#) to illustrate the progress of the
                   package installation.
--force        Install the package even if it already is installed, install an older
                   version or replace files already installed.
--nodeps     Do not perform dependency checks before installing or upgrading
                   a package.
--test           Do not install the package or upgrade the database, just identify
                   and display possible conflicts or dependency errors.

In your installation CD-ROM RPMs are stored under REDHAT/RPMS directory. For installing software packages from the installation CD-ROM do the following steps.

Installing Packages:

Insert the CD-ROM in the drive mount the cdrom and select the package to install. Alternatively you can change your directory to the place where the RPMs have been downloaded.

#mount /dev/cdrom /mnt/cdrom or /media/cdrom
#cd /mnt/cdrom
#rpm -ivh firefox.9.0.0.1-0.1.mga1.x86_64.rpm

The next example shows the error generated by trying to install a package which is already installed. To work around we use the '--force' option.

#rpm -ivh firefox.9.0.0.1-0.1.mga1.x86_64.rpm
#rpm -ivh --force firefox.9.0.0.1-0.1.mga1.x86_64.rpm

Upgrading Packages:

The option for upgrading existing RPMs comes in 2 flavour , -U for gpgrade and -F for freshen. Upgrade will install the package even if an earlier version is not currently installed, but freshening package installs only if an earlier version is currently installed.

#rpm -Uvh firefox.9.0.0.1-0.1.mga1.x86_64.rpm

Note: You can use a program called 'alien' to convert between packages like rpm, dpkg, stampede sle and slackware tgz file formats.

The following table illustrates methods of using the RedHat Package Manager.

Question	RPM Command
How do I install a new package or upgrade it if it already exists?	#rpm -Uvh package.rpm
If I have a diretory containing updated packages, how do I insatll the only the ones that are currently in my system?	#rpm -Fvh *.rpm
How do I delete an insallted packase from my computer?	#rpm -e package
How do I see a list of all installed packages on my computer	#rpm -qa \| less
I don't know what a certain installed package does. How can I get it to tell me about itself?	#rpm -qi package
How do I ask what files were installed by a package?	#rpm -ql package
There's a file in my system called /apth/to/file. How can i find out which package installed it?	#rpm -qf /path/to/file
How do I find out which package installed /apth/to/file and how do I get information on that package and see the other file that were installed by the package	#rpm -qifl /path/to/file
I delete a few files by accident but I don't know what are they. Can RPM chow me which files in its database are now missing?	#rpm -Va
'#rpm -Va' is taking a log time. How do I just verify that a certain package is OK?	#rpm -Vv package
I've downloaded an RPM package containing source code. How do I make a binary RPM out of it and then install it?	#rpm -ivh package.src.rpm #cd /usr/src/redhat/SPECS/ #rpmbuild -ba package.spec #cd /usr/src/redhat/RPMS/i386 #rpm -ivh package.rpm
How do I compress and rebuild my computer's RPM database?	#rpm -rebuilddb

Networking In Linux

2012-02-28T12:34:00.002+05:30

Networking In Linux

Descriptions:

Any system if needed to connect to the Internet, would require the networking components configured. Linux offers various methods to control the network interfaces of a system which will be explored .
Linux provides excellent support for networking and configuration of the various options via the command line as well as built-in configuration tools.

Gathering network information and setting IP addresses:

The first step is to find the IP address and the currently active interfaces in the system that we are using. Use the command 'ifconfig' to get a list of all active interfaces in the system.

Use the same command with the -a switch to get a list of all interfaces.

#ifconfig

eth0      Link encap:Ethernet HWaddr b8:ac:6f:b5:8a:3a
          inet addr:10.112.18.76 Bcast:10.112.255.255 Mask:255.255.0.0
          inet6 addr: fe80::baac:6fff:feb5:8a3a/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:110687304 errors:0 dropped:0 overruns:0 frame:0
          TX packets:84807708 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:3862591144 (3.8 GB) TX bytes:2051180865 (2.0 GB)
          Interrupt:18

lo        Link encap:Local Loopback
          inet addr:127.0.0.1 Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING MTU:16436 Metric:1
          RX packets:1098 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1098 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:610070 (610.0 KB) TX bytes:610070 (610.0 KB)

We assign an IP address to the interface 'eth0' using the command line as follows :

#ifconfig eth0 192.168.1.1 netmask 255.255.255.0

we also check if the changes have taken place using the 'ifconfig' command. You may not give the subnet mask value if you want the default ones to be used.

#ifconfig eth0

However this assignment of the IP address is only a temporary one and will be lost upon the next system reboot or restart of the network services.

To prevent this from happening and the avoid the setting of the IP address for each session, edit the configuration file for the interface which is located in the '/etc/sysconfig/network-script' directory. The file will be called 'ifcfg-'. In our example, the file will be called 'ifcfg-eth0'.

Edit the lines in the original file which is as follows:

DEVICE=eth0
BOOTPROTO=dhcp
HWADDR=08:0027:27:57:52
ONBOOT=yes
TYPE=Ethernet

To read as follows

DEVICE=eth0
BOOTPROTO=static
HWADDR=08:0027:27:57:52
ONBOOT=yes
TYPE=Ethernet
IPADDR= 192.168.1.1 --------------------------------------> IP address
NETMASK= 255.255.2555.0 ---------------------------> subnet mask

From the next boot onward the system will take the IP address that you designated.

Adding and Deleting gateway in Linux:

The IP address assigned so far would only allow for communication between system in the same subnet. To add support for communications to other subnets, we need to add gateways to the system.

We add default gateway to the system by using the 'route' command.

#route add default gw 192.168.1.254

We can add a dedicated route to a particular network or host by issuing the route command but with a few changes to the command used above.

#route add -net 10.0.0.0 netmask 255.255.255.0 gw 192.168.1.10
#route add -host 172.16.1.1 gw 192.168.1.11

To look at the current routing table in the kernel we use the same command but this time without any arguments. However we can use the '-n' switch which will give the output in the numeric format.

#route -n

To delete a route we use the 'route' command itself but with the 'del' option passed instead of the 'add'.

#route del -net 10.0.0.0 netmask 255.255.255.0

A look at the kernel routing table shows that the route to the 10.0.0.0/32 network no longer exists.

#route -n

Using the 'system-config-network' tool:

Open a terminal and type 'system-config-netowrk'

In the monitor we will see network configuration tool Utility.

Select the interface whose properties you wish to change and click edit. A screen as shown on monitor.

Choose the properties of the interface as per your requirements.

To add route to the system click on the Route tab.

Click on 'Add' icon and you will configure IP address and Subnet Mask , Gateway.

Finally you can delete a route by selecting the route and then clicking 'Delete' in the 'Route' tab.

Disk Management in Linux

2012-02-28T11:49:00.002+05:30

Disk Management in Linux

Descriptions:

Secondary storage forms the fundamental part of any computing infrastructure. System administrators are expected to utilize hard drives effectively to help users in optimizing their productivity. Using command line tools to manage hard disks in linux.

Introduction:

Linux offers utilities to manage hard disks. Users may add, delete change partition types. Furthermore they can also implement software RIAD, LVM etc using command line utility.

Here are a few caveats regarding hard disks.

A disk drive requires a partition table.

The partition is the logical sequence of cylinders in the disk.

A cylinder represents all the sectors that can be read by all heads with on movement of the arm that contains all these heads.

Linux supports up to 16 partitions on any individual IDE or SCSI drive.

Primary partitions: 3 , Extended partition: 1, Logical partition:12

Hard Disk Overview:

Firstly we start off by inspecting the hard disk for its current set-up. Our aim now is to find the partitions and their types those are currently existing. All commands need to be executed as the 'root' user. Hard disks are detected in the location /dev/hda'n' ( for IDE drvies) or /dev/sda'n' ( for SATA/SCSI drives). The 'n' denotes the partition number in that hard drive. Primary partitions are numbered from 1-3 and extended partition is given the number 4. All logical partitions are given numbers 5 onwards. However, the conventions differ as per the distribution of linux that you are using.

The 'a' in the hda (or sda) is the location of the hard disk controller where the hard drive is connected. So for IDE drives, 'a' is the primary master channel, 'b' is the primary slave channel, 'c' is the secondary master channel, 'd' is the secondary slave channel. Accordingly the location where the hard disk gets read would change to either /dev/had, /dev/hdb , /dev/hdc, or /dev/hdd.

In my system that has 2 hard disks, a 500 GB primary master and a 1 TB primary slave, I execute the following commands. I have just added the 1 TB partition. So lets perform all our operation in this hard drive only.

#fdisk -l

Disk /dev/sda: 320.1 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000080

   Device Boot      Start         End      Blocks   Id System
/dev/sda1   *           1          25      194560   83 Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              25       38914   312373249    5 Extended
/dev/sda5              25         523     3998720   82 Linux swap / Solaris
/dev/sda6             523       38914   308373504   83 Linux

When I gave this command without specifying the device, I get a list of all hard drives and I get an informatory messages that the hard disk /dev/hdb has no valid partition table. Also the hard drives are recognized as IDE hard drives in slots 'a' and 'b'. To get details regarding only one hard drive, pass the location of the hard disk to the same command.

#fdisk -l /dev/hda

Lets analyses the output:

The command request the details of the hard disk attached to /dev/hda.

The output first gives the human-readable ( MB, GB etc.) size of the hard disk.

Next it gives the actual size of the hard disk in bytes.

Next are a few details on the number of heads, sectors and the total number of cylinders in the hard disk.

Then the details of the partitions are given. Each column is as follows.

Title	Explanation
Device	The absolute path to the partition
Boot	Specifies which partition is bootable. An asterisk in marked to designated this partition
Start	The starting cylinder of the partition
End	The last cylinder of the partition
Blocks	The number of blocks in that partition
Id	The file system id, a hexadecimal number to denore the file system in the partition
System	The type of the partition. A human-understandable format

Creation and Deletion of partitions :

As we have a 4 GB hard disk that does not have a partition table. We will create 2 partition in it.

We use the fdisk to create partition in the second hard drive.

#fdisk /dev/hdb

Pressing 'm' will display the help for you.

We create a new primary partitions occupying 6000 cylinders for the first one and the remaining for the second partition which will be an extended partition. Note: You can create a partition of a specific size that you want. Just rad the option carefully. Pressing ENTER at any question will take the default value for that question, if there is any.

Command ( m for help): n

We look at the partition table by pressing 'p'

The changes we made so far only temporary and will be finalized to the disk only when you explicitly order 'fdisk' to do so. Confirm changes using the 'w' option. The 'q' option will quit without saving changes.

Command (m for help): w

This creates the partition in the hard disk. But the changes are not yet read by the Operation System. The next step is no make the kernel re-read the partition in the hdb device.

# partprobe /dev/hdb

We next make the filesystem that linux can read in the partition hdb1.

#mkfs.ext3 /dev/hdb1 ( partition name )

Similarly we add a filesystem to the hdb2 partition as well

#mkfs.ext3 /dev/hdb2

The deletion of a partition can be accomplished by typing 'd' and corresponding number of the partition which you want to delete when prompted for one.

SAMBA Server

2012-02-24T12:52:00.000+05:30

SAMBA Server Configuration

Descriptions:

The presence of linux workstation in a network will invariable demand the need for allowing remote file access in between systems. Samba is a solution that is used to enable UNIX-Windows file sharing. Readers implements a samba server in the network so that other users of the LAN can leverage the functionalities of network file sharing.

Introduction:

Samba is a suite of programs running under UNIX-like operating systems that provide integration between unix and windows machines. Samba uses server Server Message Block ( SMB ) protocol which is the underlying protocol used in Microsoft Windows Networking.

For many networks samba can provide a complete replacement for windows NT servers, although it does not provide the full range of functionality provided by Active Directory under Windows Server 2000 and Windows server 2003.

Samba can also register itself with the master browser on the network so that it would appear in the listing of hosts in windows 95/NT "neighborhood network". In fact, samba itself can act as the master browser ( domain controller ) on the network.

Samba can also use LDAP ( Lightweight Directory Access Protocol ) as backend database for storing machine and user account details.

Another standard feature of Samba is an ftp like SMB client which allows you to access shared PC resources such as disk or folders and printers.

Packages that are required to have Samba system in the system are shown below.

Package	Description
Samba-*	Basic Samba Server Package
Samba-client-*	This package allows you to setup your linux computer to read shared Microsoft Printers
Samba-common-*	This package includes files required to support Linux as a Samba client and as a samba server.
Samba-swat-*	This GUI tool lets you modify the main samba configuration files.

Configuring a share :

To analyze the way directory are share from the packaged 'smb.cong' configuration. There are 8 examples of shared directories in the standard 'smb.conf' file.

SAMBA Linux to Windows Sharing

Setup the shares in /etc/samba/smb.conf by editing it as follows
[share1] -----------------------------------------------------> This is the share name
          comment = share from linux box ----> A description of the share
          path = /path/to/shared/directory -----> Path to the shared directory
          read only - yes/no ----------------------------> Permissions to the directory
          vaild users = user ---------------------------> User name
          browse able = yes/no ----------------------> Permission to list contents of the
                                                                       directory
If you want to share CD/DVD drive
[DVD]
         comment = dvd drive on linux box
         writable = no
         locking = no
         path = /mount/point/of/dvd
         valid users = user1 ( user name )

Checking the configuration file for errors:

After editing the 'smb.conf' file to add the shares that you need, we check it for consistency and syntactic errors.

At the shell type:

#testparm

this command reads through the configuration file and display errors if any.

Adding Users:
At this stage, we are almost done. To access Samba shares, evey user needs to have a userID and password. Bear in the mind that this userID and passwd is different from the log-in ID that the users uses to log in to the system.
Open your terminal windows and type in the following:
#useradd user1
#passwd user1
changing password for user user1
NEW UNIX password:
Retype new UNIX password:
passwd: all authentication tokens updated successfully

#smbpasswd -a user1
NEW SMB password:
Retype new SMB password:
Added user user1

The same username and password that you log onto to the windows PC with.
When you create a new linux user, it will automatically create a home share for this person. In this case it will be /home/user1.
Now Samba has to be restarted so that all of the changes that we have made will take effect. For starting that samba services use the following command in the command prompt.

#/etc/init.d/smb restart OR
#/etc/init.d/smb start

Accessing the shares via GUI:
Accessing shares from a windows machine.

Click Start|Run.
In the prompt type \\192.168.0.1\share1. 192.168.0.1 is the IP address of the linux machine.

Accessing shares from a linux machine.

Open a file browser like nautilus or knoqueror.
Type 'smb://192.168.0.1/share1' and press enter to access the share.

Accessing the shares via command line in Linux:
you can access share available from linux machine by mounting the share as your local directory. For mounting use the following command on the client linux machine.
#smbmount //linuxserver/share name /home/user1 -o username= test password:

OR
$smbclient //linuxserver/sharename -u username
password:
smb:/>

Note:
To access the smb share via a remote machine, we need to know the username and password on the remote samba server machine.

Global Parameters
[global]
Anything in here applies to samba as a global setting. There is some configuration info here that is important so that samba and your windows pc's will function properly. However some global settings can be overridden by share settings ( more on this later). I will now go through each line and give a brife description of what role it plays in Samba.

workgroup = home
This is the name of your network group. It is important that both samba and windows are in the same workgroup. Please read your windows documentation on how to change your windows pc's workgroup name.

netbios = Samba
Netbios name is what you will see in your windows pc "Network Neighborhood"
for your Samba server. You can name this anything you wish. If you leave it blank, it will default to your host name.

encrypt passwords = yes
Samba can work with encrypted or unencrypted passwords. However windows 98, Windows NT,2000 utilize encrypted passwords. The only time this should be set to no is when you have any older windows systems running on your network ie: Windows 95,3.x if this is the case you will have to do some registry modifications to your windows 98, NT , 2000 to allow them to send unencrypted passwords across the network. Not the most secure situation though.

Share Parameters
[homes]
When you create a user on your linux pc ( more on this later ) it will automatically create a home folder for you in /home/yourusername. Think of this as your "My Documents" for linux.
read only = no
By default samba will always make any directory read only for security reasons, so we need to let samba know that we want to be able to write to this directory.
browseable = no: defines when you map a network drive to samba, it will map directly to your user directory ie: \\home\mw ( this is my username on linux and samba ) This share /home/mw is browseable only by you. Remember this is much the same as the " My Documents" folder in windows.
path = /data/mp3
This tells us the directory is found on the samba server as /data/mp3, later when we map the network drive on the windows pc, it will be seen as "music" in Network Neighborhood.
browseable = yes
This share will show in network neighborhood as " Music "
Public = yes
Specifies anyone can access and view the contents of /data/mp3
write list = user1
Although anyone can view and excute ( meaning see and play any mp3 in this directory ). For security and practical reason i have set this share so only mw ( thats me ) and jackie can delete or add files. You can add as many names as you wish to this line ie: , mw, john, tiffany etc. To exclude any person from being able to access this share altogether, add the line: invalid users = vicky, steve. These names are the logon names from windows and are not case sensitive. They also must have a logon name and samba password on the linux pc.

Network Information Services

2012-02-23T13:12:00.000+05:30

Network Information Services ( NIS )

Descriptions :

The existence of a centralized log on system eases the administrative burdens of network and systems administrators. NIS is one such implementation for linux domains.

Introduction:

Network Information Servies ( NIS ) enables you to create user accounts that can be shared across all systems on your network. The user account is crated only on the NIS server. NIS clinets downloads the necessary user name and password data from the NIS server to verify each user login.

Network Information Services ( NIS ) originally known as yellow pages, is sometimes called Name Services and follows the client-server architecture. NIS servers maintain replicated servers, with the principal servers being referred to as master servers and the replicated serves referred to as replica or slave servers.

NIS master and replica servers provide services to NIS clients. NIS stores information on the master server in a set of files called maps about users, groups, hosts information, address, and network services information. This collection of network information is referred to as the NIS name space.

NIS maps store information in a two column table. The first column lists the key and the other column display information about the key. The NIS server responds to the client query based on the information in the maps.

An advantage of NIS is that users need to change their passwords on the NIS server only. instead of every system on the network. This makes NIS popular in computer training labs, distributed software development projects or any other situation where group of people have to share many different computers.

The disadvantages are that NIS doesn't encrypt the user name and password information send to the client with each login and that all users have access to the encrypted passwords stored on the NIS server.

The Lightweight Directory Access Protocol ( LDAP ) offers similar features to NIS but has the advantage of supporting encryption without additional software and can support clients across multiple networks without the need for slave servers. It is for this reason that LDAP has became increasingly popular for this type of application.

Packages required for NIS server and client configuration are given below:

ypserve , yp-tools ------------ server configuration
ypbind , yp-tools ------------ client configuration

So before configuration NIS check whether these package are present both in server and client systems by typing the following command in the command prompt.

# rpm -qa yp*

Configuring Network Fine System :

Configuring NFS on server side :

The need for configuring NFS in NIS server is to make the users home directories available across all the remaining linux workstations in the local network. So to export the users home directories across network go to /etc/exports and add the following line

/home    *(rw,sync)

and save changes to the file and come back to the command prompt and type exportfs -a to export users home directories across the network.

Make sure the required nfs, nfslock and portmap daemons are running.

Configuring NFS on client side:

On client side to mount the users respective home directories when they access NIS server for login, create a directory by name home to mount your home directory on the serve to the newly created home directory on the machine from where we are going to access the NFS server. For mounting use the following command.

# mount 192.168.53.2:/home /home/
# mount IP Address:/direcotry /path/

Here 192.168.53.2:/home is home directory of user situated on the NFS server and /home is directory created in the client system.

To unmount the home directory use umount /home.

The other way of mounting the home directory if the user is using auto mounting option. Start configuring auto fs auto mounting. Edit your /etc/auto.master file to refer to file /etc/auto.home for mounting information whenever the /home directory is accessed. After five minutes, autofs umounts the directory.

# vim /etc/auto.master
/home                /etc/auto.home --timeout 600

Edit file /etc/auto.home to do the NIS mount whenever the /home directory is accessed. If the line is too long to view on your screen, you can add a \ character at the end to continue on the next line.

# vim /etc/auto.home

*       -fstype=nfs,soft,intr,rsize=8192,wsize=8192,nosuid,tcp \192.168.53.2:/home:&

Start autofs and make sure it starts after the next reboot with the chkconfig command.

#chkconfig autofs on
#service autofs restart

Configuring NIS Server :

Before configuring NIS server make sure that all the NIS related packages are installed and if not install the required packages. After installing the required packages follow the steps given below for configuring NIS.

In /etc/sysconfig/network file and add the domain name as test.com

# vim /etc/sysconfig/network
NISDOMAIN= "test.com"

Now edit the /etc/yp.conf file since NIS server also have to be NIS clients themselves, so you'll have to edit the NIS client configuration file /etc/yp.conf to list the domain's NIS server as being the server itself or local host.

# /etc/yp.conf -ypbind configuration file
ypserver 127.0.0.1

Start the necessary NIS daemons and use the chkconfig command to ensure they start after the next reboot.

# service portmap start
# service yppasswdd start
# service ypserv start
# chkconfig portmap on
# chkconfig yppasswdd on
# chkconfig ypserv on

Brief description of each daemon is shown below :

Daemon Name	Purpose
Portmap	The foundation RPC daemon upon which NIS runs.
Yppasswdd	Lets users change their passwords on the NIS server from NIS clients
Ypserv	Main NIS server daemon
Ypbind	Main NIS client daemon
Ypxfrd	Used to speed up the fransfer of very large NIS maps

To make sure they that all the daemon are running properly, you can use the rpcinfo command from the command prompt.

Initializing NIS Domain:
To create the associated authentication file for the domain we use ypinit command. When you use this command it will prompt for the domain name at some time where we have to specify test.com. Before running this command sure that port map service is running on your system. Use ypinit command as shown below.

# /usr/lib/yp/ypinit -m

At this point, we have to construct a list of the hosts which will run NIS servers. 'user1' is in the list of NIS server hosts. Please continue to add the names for the other hosts, one per line. When you are done with the list, type a "control D".

next host to add: test.com
next host to add:
The current list of NIS servers looks like this:
user1
Is this correct? [y/n] = y
user1 has been set up as a NIS master server.
Now you can run ypinit -s user1 on all slave server.
#
Now start running ypbind and ypxfrd services from the command promp.

Configuring NIS client:
Now on the client side run authconfig command. The authconfig or the authconfig-tui program automatically configures your NIS files after prompting you for the IP address and domain of the NIS server.
#authconfig-tui

Once finished, it should create an /etc/yp.conf file that defines, amongst other things the IP address of the NIS server for a particular domain. It also edit the /etc/sysconfig/network file to define the NIS domain to which the NIS client belongs. In addition, the authconfig program updates the /etc/nsswitch.conf file that lists the order in which certain data sources should be searched for name lookups such as those in DNS, LDAP and NIS.

You can also make changes manually by making changes for the following files as shown below.

In /etc/sysconfig/network file and add the domain name as test.com.
#/etc/sysconfig/network
NISDOMAIN="test.com"

Now edit the /etc/yp.conf file since NIS servers also have to be NIS clients themselves, so you'll have to edit the NIS client configuration file /etc/yp.conf to list the domain's NIS server as being the server itself or local host.

#/etc/yp.conf - ypbind configuration file
ypserver 192.168.53.2

In /etc/nsswitch.conf file, that lists the order in which certain data sources should be searched for name lookups such as those in DNS, LDAP and NIS. Here you can see where NIS entries were added for the important login files.

#/etc/nsswitch.conf
passwd: files nis
shadow: files nis
group: files nis

After completing the editing of files start client service daemons ypbind and port map and verify that they are automatically starting at reboot.

Testing the NIS Server:
For testing access to NIS server you can ru nthe ypcat, ypmatch and getent commands to make sure communication to the server is correct.

#ypcat passwd
#ypmatch user1 passwd
#getent passwd user1

Network File System

2012-02-22T16:22:00.002+05:30

Network File System ( NFS )

Descriptions :
The presence of Linux workstation in a network will invariably demand the need for allowing remote file access in between system. NFS is a solution that is used to enable UNIX-UNIX file sharing. Implement a NFS server in the network so that other users of the LAN can leverage the functionalities of network file sharing.

Introduction:

NFS ( Network File System ) allows hosts to mount partitions on a remote system and use them as though they are local file systems. This allows the system administrators to store resources in a central location on the network, providing authorized users continuous access to them.

Package required for NFS:

Nfs-utils-* Include basic NFS commands and daemons
Portmap-* Supports secure NFS.RPC connections

Editing the configuration file:

To configure NFS you have to configure /etc/exports file. This is the place where you are going to mount file system that is to be shared in the network. In order to export a particular file system, we have specify it in the following format as shown below in /etc/exports file.

export host1(options)------------------------- hostN(options)

In the above format, in the place of export place the directory which you want to export. In the place of host1 specify the ip address or the network address so that a particular network can access the exported directory. And the options include read and permissions,user permissions etc.

The following methods can be used to specify host names in place of host1:

single host --- Where one particular host is specified with fully qualified domain name, hostname, or IP Address.

wildcards ---- Where a * or ? character is used to take into account a grouping of fully qualified domain names that match a particular string of letters. Wildcards should not be used with IP Address; however, it is possible for them to work accidentally if reverse DNS lookups fail.

Be careful when using wildcards with fully qualified domain names, as they tend to be more exact than expected. For example the use of *.example.com as a wildcard allows sales.example.com to access and exported file system but not bob.sales.example.com. To match both possibilities both *.example.com and *.*.example.com must be specified.

IP networks --- Allows the matching of hosts based on their IP address within a larger network. For example, 192.168.0.0/28 allows the first 16 IP address, from 192.168.0.0 to 192.168.0.15, to access the exported file system but not 192.168.0.16 and higher.

OPTION	DESCRIPTION
ro	Read Only permission
rw	Read and Write permission
sync	All data is written by request
no_root_squash	Allow root user to access exported directory through network
hide	Sharing the directory without including its sub directories for sharing
no_hide	Includes sharing sub directories
no_wdelay	Data is written to share immediately

all_squash

Treat all users as anonymous users

Example :
An example for how to enter a directory in /etc/exports file for exporting is given below:
/home user.test.com(rw,sync)
/user1 *.test.com(rw,no_root_squash,sync)

Here in the first line the home directory can be accessed only by user.test.com. Where as in the second line user1 directory can be accessed by any system in the test.com domain. Here '*' is a wild card which specifies all clients in the domain test.com.

Exporting Files:

After specifying the directory which we want to export in the /etc/exports file, save the configuration and come out of the file and start the nfs service through command prompt using command service portmap start or /etc/init.d/portmap start.
Now for exporting the specified directory,in the command prompt use the following commands.

Command	Description
exportfs -a	Exports all directories for sharing specified in /etc/exports
exportfs -r	Receives list of shared directories after changing the configuration file
exportfs -u	Unexports all directories
exportfs -v	Lists all currently shared directories

Configuration on the client side for accessing directories exports through NFS:
On the client side, in order to view the directories that are exported through NFS use the following command.

#shownmount -e hostname ( IP Address of server )
Which shows all shared files. If you want to mount that directory locally you'll need an empty local directory. So create a directory such as /home/test. Now we can mount the share directory from a particular computer with the following command.
# mount -t nfs enterprise3:/usr/loca /home/test
# mount -t nfs IP address hostname:/server side directory /user side directory
In the above command, enterprise3 is the computer name from where the directory is exported and /usr/local is the exported directory and /home/test is the place where we have mounted the exported directory on to the machine through which you are accessing. '-t nfs' specifies the type of file system.
NOTE:

A file system is a method for storing and organizing computer files and the data they contain to make it easy to find and access them. File systems may use a data storage device such as a hard disk or CD-ROM and involve maintaining the physical location of the files.

Portmap service is required to map RPC requests to the correct services. When ever a client contacts the Portmap server with some RPC number the Portmap redirects the client to the intended service.

RPC ( remote procedure call ) is a protocol that one program can use to request service from a program located in another computer in a network without having to understand network details. RPC uses client/server model. The requesting program is a client and service providing program is the server.

FTP Server

2012-02-21T17:11:00.000+05:30

File Transfer Protocol ( FTP )

Description:

Linux offers powerful networking capabilities. Consequently it has become one of most popular Operating System that make the backbone of the world wide web. One of the popular method of hosting services across the Internet is the use of FTP server that use the File Transfer Protocol to aid file transfers across the Internet. Set-up FTP server for various access needs.

Introduction:

If you want to enable other users to download files from a location on your server's hard disk or to upload file to that location then one solution is to set-up an FTP server.

When users want to upload/download from your FTP server they use a program called the FTP client.

These communications between the FTP server and FTP client takes place using the File Transfer Protocol ( FTP ).

FTP is not considered a secure protocol as communications between the FTP client and server are unencrypted. Consequently Secure FTP ( SFTP ) is gaining popularity among users.

Many FTP servers still its disk space and download its files. Anonymous FTP access is used mostly to enable users to access freely available documents program etc. via the internet without access control.
530 Please login with USER and PASS.

FTP Servers included in Linux

Very Secure File Transfer Protocol Daemon ( vsftpd )
TUX
wu-ftpd
gssftpd

Installing the vsftpd FTP server:

Depending on the choices chosen during installation, the FTP daemon may have been installed.

Check for it in Applications|System Settings|Add/Remove Application . Check the check box for the vsftp package.

To start the FTP service ( enabling users to upload/download files), we can use the services configuration tool located in Application|system Settings|Server Setting|Srvices.

Alternatively type service-config-services at the command line.

Select vsftpd in the list and then click the start button.

Click on file save it.

From the command line, use the service command.

# service vsftp start ( to start the service )
# service vsftp stop ( to stop the service )

The commands shown above are specific to Linux. A more generic command.

# /etc/init.d/vsftpd start
# /etc/init.d/vsftpd stop

Testing the FTP server :

Now you have setup the FTP server and started the service, we'll adopt the role of the client to quickly test the server. From the command line type the command.

#ftp
   Connected to host.domain/ip-address.
   220 (vsFTPd version)
   530 Please login with USER and PASS.
   530 Please login with USER and PASS.
   KERBEROS_V4 rejected asan authentication type
   Name (ip-address:root):anonymous
   331 Please specify the password.
   Password:
   230 Login successful.
   Remote system type is UNIX.
   Using binary mode to transfer files.
   ftp> bye
   221 Goodbye.

Configuring an anonymous FTP for file download:

Anonymous users can not read form any directory from the machine in which the server is hosted.

By default the vsftpd package creates a directory tree starting ar /var/ftp/pub and enables anonymous read access to this directory. Anonymous users connect to the /var/ftp directory when they establish a session with the FTP server.

Setting Up the FTP server:

Place some content in the /vat/ftp/pub directory so that other users can access it.
The owner of l the /var/ftp/pub is the root account and is only permitted to that directory.

Using and FTP client to test anonymous read access:

Now you can test for anonymous access by using an FTP client to try grab a copy of this file via FTP connection.
Both Windows and Linux machines can use FTP using the command line.
FTP clients are given as a default package on the installation of the system.
Connect to the FTP server and log in as the anonymous user.

$ ftp 192.168.53.77 ( ip address )
Connected to 192.168.53.77.
220 ( vsFTPd 2.0.5 )
Name (192.168.53.77:user):anonymous
331 Please specify the password.
Password:
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp>

You can list the files in the current directory. This is the directory where you connected.

ftp> ls
200 PORT command successful. Consider using PASV.
150 Here comes the directory listing.
-rw-r--r-- 1 0 0 21 feb 13 11.14 file 1
226 Directory send OK.

Any Linux command related to file system navigation will be executed in the server. To execute a command in the local system, precede the command with an exclamation mark (!). To change the local directory , use the 'lcd' commad.

ftp> !pwd
/home/user/Desktop
ftp>lcd~
Local directory now /home/user

To download a file, use the 'get' command. To get multiple files, use the 'mget' command.

ftp> get file1
local: file 1 remote: file 1
200 PORT command successful. Consider using PASV.
150 Opening BINARY mode data connection for file 1 ( 16 bytes ).
226 File send OK.
16 bytes received in 0.00 secs ( 84.0 kB/s )

To exit out of the session, use the bye command.

ftp> bye
221 Goodbye.
$

Configuring and anonymous FTP server for file upload :

Anonymous FTP users can write only into directories that we allow them to write to.

By default, vsftpd dose not allow users to upload to the FTP server at all; we must first configure the server to allow anonymous users to write to some directory.

Setting up the FTP server for Anonymous write access:

To create a writable directory, you'll need the root account for this. Let's cerate a directory called 'uploads' in the /var/ftp/pub directory.

# mkdir /var/ftp/pub/uploads

To set the permission of the upload directory so that it allows write only access to anonymous FTP users.

# chgrp ftp /var/ftp/pub/uploads
# chmod -R 730 /var/ftp/pub/uploads

To configure the vsftpd server to allow anonymous upload, edit the configuration file /etc/vdftpd/vsftpd.conf.

#Uncomment this to allow the anonymous FTP user to upload files. This only
#has an effect if the above global write enable is activated. Also, you will
#obviously need to create a directory a directory writable by the FTP user.
#anon_upload_enable = YES

Remove the hash in front of the previous line. It should now look like.

anon_upload_enable=YES

Restart the FTP service for the changes to take effect.

Using an FTP client to test anonymous write access:

Connect to the server and authenticate as anonymous user.

$ftp 10.0.2.15
Connected to 10.0.2.15.
220 ( vsFTPd 2.0.1 )
530 Please login with USER and PASS.
530 Please login with USER and PASS.
KERBEROS_V4 rejected as an authentication type.
Name (10.0.2.15:root): anonymous
331 Please specify the password.
Password:
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp>

Change to the directory in which you have write permissions.

ftp> cd pub/uploads
250 Directory successfully changed.
ftp>

Upload the file you want using the 'put' command. For multiple files use the 'mput' command.

ftp> put ftp
local:ftp remote:ftp
227 Entering Passive Mode (10,0,2,15,110,4)
150 Ok to send data.
226 File receive OK.
575 bytes send in 0.00027 seconds (2.1e+03 Kbytes/s)
ftp>

FTP authentication vis a system account :

Your system has an user account called 'user'. This account can be used to gain access to the FTP server. These users will be presented their HOME directories to work with.

$ ftp 10.0.2.15
Connected to 10.0.2.15.
220 (vsftpd 2.0.1)
530 Please login with USER and PASS.
530 Please login with USER and PASS.
KERBERROS_V4 rejected as an authentication type
Name (10.0.2.15:root):user
331 Please specify the password.
Password:
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp>

Disabling Local System Users Account for FTP:

By default the users logged in through FTP would have the same permission to read, write and execute the contents of their home directory via FTP that they would have had if they were accessing the directory by logging in at the computer.

Authentication via FTP is not encrypted so allowing FTP via user accounts is actually not a good idea to allow access to your system if you have got anything sensitive to protect.

Edit the vsftpd configuration file to disallow access to the system users and comment the following line.

# Uncomment this to allow local users to log in.
local_enable=Yes

This line should then read as

# uncomment this to allow local users to log in.
# local_enable=YES

Blocking FTP Access for selected user account:

To deny FTP access to individual users edit the vdftpd configuration file to allow system users access to the FTP server.

Edit the /etc/vsftpd.ftpusers file. This file contains the list of system users no allowed to access to the FTP server.

Add the name of the users that you want to deny access to. In the lab,we add the user 'user'.
Save and Exit and restart the FTP server daemon.

Try logging in as the user.

$ftp 10.0.2.15
connected to 10.0.2.15.
220 (vdftpd 2.0.2)
530 Please login with USER and PASS.
530 Please login with USER and PASS.
KERBEROS_V4 rejected as an authentication type
Name (10.0.2.15:root):user
331 Please specify the password.
Password:
530 Login incorrect.
Login failed.
ftp>

Configuring an FTP greeting banner:

Open the vdftpd configuration file for editing.

Search for the line that asks you to customize a login banner.

# you may fully customize the login banner string:
# ftpd_banner=welcome to -------- services.

Uncomment the line that says 'ftpd_banner' and write and appropriate login banner.

Restart the FTP server and see if your banner has taken effect.

$ftp 10.0.2.15
connected to 10.0.2.15.
220 Welcome to the ------------ service.
Name (10.0.2.15:root):

DHCP Server

2012-02-20T17:31:00.000+05:30

Dynamic Host Configuration Protocol ( DHCP )

Description

For the management of large networks, assignment of the ip addresses statically
may prove to be a tedious task for the administrator. A solution is to automatic
ip address assignment to the users via a Dynamic Host Configuration Protocol
( DHCP ) Server. Aims to get the readers to deploy a DHCP server in the network.

Introduction

It is a network protocol that enable a DHCP server to automatically assign an IP address to an individual computer. DHCP assigns a number dynamically from a defined range of number ( i.e., a scope ) configured for a given network.

Client computer configured to use DHCP for IP assignment do not need to have a statically assigned IP address.

DHCP assigns a TCP/IP address when a system is started. Typically, it works like this:

1. A user turns on a computer with a DHCP client.
2. The client computer sends a broadcast request ( called DISCOVER or
     DHCPDISCOVER ), looking for a DHCP server to answer.
3. The router directs the DISCOVER packet to the correct DHCP server.
4.   The server receives the DISCOVER packet. Based on availability and usage
      policies set on the server, the server determines an appropriate address
      ( if any ) to give to the client. The server then temporarily reserves that
     address for the client and sends back to the client an OFFER ( or
     DHCPOFFER) packet, with that address information. The server also
     configures the client's DNS server, WINS serves, NTP servers and some-
     -times other services as well.
5. The client sends a REQUEST ( or DHCPREQUEST ) packet, letting the server
     know that it intends to use the address.
6. The server sends an ACK ( or DHCPACK ) packet, confirming that the client
      has a been given a lease on the address for a server-specified period of time.

The DORA process in DHCP works as follows.

D ----------> Discover

O ----------> Offer

R ----------> Request

A ----------> Acknowledgement

1. Client makes a UDP Broadcast to the server with a DHCPDiscover, or
     Discover packet.
2. DHCP offers to the client.
     The server sends a DHCPOffer including other configuration parameters
     (DHCP Options) for the client per the servers configuration file
3. In response to the offer Client requests the server.
     The client replies DHCPRequest, unicast to the server, requesting the
     offered address.
4. The server sends DHCPAck acknowledging the request which is the clients
     final permission to take the address as offered. Before sending the ack the
     server double checks that the offered address is still available, that the
     parameters match the clients request and (if so) marks the address taken.

DHCP Installation and Configuration

Start the Linux machine and check if the DHCP server packages are installed.

# rpm -qa dhcp

# rpm -ivh dhcp*

If you see the output show above the packages are installed or else you needto install them. However the version shown above might change depending on the version of the OS used.

Now open the file /etc/sysconfig /dhcpd and edit the line as follows. The line which reads

DHCPARGS=

must now read.

DHCPARGS=eth0

Replace 'eth0' above with the network interface you want to use for dhcp.

Now copy /usr/share/doc/dhcp-version naem/dhcp.conf.sample to /etc/ by name ' dhcpd.cof ' by typing the following command in the command prompt.

# cp /usr/share/doc/dhcp-version name/dhcpd.conf.sample /etc/dhcpd.conf

You can also copy the configuration file from any other configured dhcp server
also.

Now edit /etc/dhcpd.conf file according to your requirements. A sample dhcp configuration file is shown below.

subnet 10.0.0.0 netmask 255.255.255.0 {
# --- default gateway
        option routers                                    10.0.0.1;
        option subnet-mask                            255.255.255.0;

#      option nis-domain     "mydomain.com";
         option domain-name     "mydomain.com";
     option domain-name-servers         216.227.56.120, 64.34.4.36; ---->name
                                                                                                                server
     option time-offset                           -28800; # Pacific Standard time
# option ntp-servers                          192.168.1.1;
# option netbios-name-servers          192.168.1.1;
#--- Select point-to-point node ( default is hybrid ). Don't change this unless
#--- you understand Netbios very well
#    option netbios-node-type 2;

      range 10.0.0.50 10.0.0.254; -------------------> range of your ip adderss
      default-lease-time 604800;
      max-lease-time 604800;

     hosts test {
#   option dhcp-client-identifier "test";
      hardware ethernet mac address 00:e0:18:90:28:b2;
fixed-address    10.0.0.10;
}
# we want the nameserver to appear at a fixed address
#    host ns {
#    next-server marvin.redhat.com;
#    hardware ethernet 12:34:56:78:AB:CD;
#    fixed-address 207.175.42.254;
#    }

}

In the above the range 10.0.0.50 to 10.0.0.254 have been set side for dynamice hosts; this allows anything between 10.0.0.1 and 10.0.0.49 to be set aside as static ips. In the example, host 'test' is given a static ip using its mac address. the option 'dhcp-client-identifier' may work as an alternative to mac address, but may require some additional configuration on the client. The max lease time of 604800 translates to 7 days. Lease times are automatically renewed by clients once 50% of the expiration date is reached. Because of this very long lease timesshould be unnecessary. If a very long one is required provide the client a static ip using the host declaration. Also the option time-offset setting is in seconds according to the manual page ; Red Hat's configuration document erroneously lists this setting in hours. Use option host-name "apex.example.com" in a host declaration to provide hostnames to clients.

Once the dhcp.conf file is configured, Start/Restart the server.

# service dhcpd start

Note: When ever you make changes to the configuration file /etc/dhcpd.conf require the dhcp server should be restarted .

And check dhcpd.lease file has been created automatically or not . If not create the file manually by using the following command .

# touch /var/lib/dhcp/dhcp.leases

The lease database is recreated from time to so that it is not too large. First all known leases are saved in temporary lease database. The dhcpd.leases file is renamed dhcpd.leases~, and the temporary lease database is written to dhcpd.leases.

Finally check whether the DHCP server is offering IP leases to clients.

Apache Web Server

2012-02-17T15:08:00.002+05:30

Apache Web Server

Descriptions and Purpose of lab exercise

Web servers are perhaps present in every data center of any organization.
There a few option from which we can choose a web server to host an
organization's web pages from. Apache is the most popular open-source web
server. This lab aims at getting the readers to implement the webserver.

Prerequisite
Should be familiar with the basic principle of server/system administration.
Additionally, prior exposure to any of these concepts can be helpful:

* Compilation of native programs (e.g. configuring and compiling c/c++
applications on UNIX/Linux)
* HTTP protocol (i.e. the stateless nature of HTTP, the need for session, HTTP
methods, SSL, etc.)

Introduction

   Apache is the most widely used web server on the internet. Based on HTTP
   daemon (hhtpd), it provides simple and secure access to all types of contents,
   based on the HTTP and HTTPS protocols.
   It is based on the server code developed by National Center for
   Supercomputing Applications (NCSA). As Apache include many patches it
   came to be known as "a patchy" server. Apache web server continues to
   advance the art of the web and provides one of the most stable,secure,robust
   and reliable web servers available. This server is under constant development
   by Apache software foundation (www.apache.org)

Features available in Apache Web Server

* Dynamic Shared Object Support
    Apache modules may now be loaded at runtime; this means that modules can
    be loaded into the server process space only when necessary, thus overall
    memory usage by Apache will be significantly reduced. DSO currently is
    supported on FreeBSD, OpenBSD, NetBSD, Linux, Solaris, SunOS, Digital
    UNIX etc.

* Support for various platforms
Apache supports the windows NT and windows 2000 operating systems.
While Apache many run on windows 95,98 or ME these consumer products
are never recommended for production environments and their use remains
experimental. All versions of apache running on windows prior to 1.3.15
should be considered beta quality release. It also supports the cygwin
platform for the windows NT and windows 2000 operating system. The
cygwin version should be considered as stable and reliable. It also supports
NetWare 5.x and above operating system.

* Reliable Piped Logs
    On almost all unix architectures apache now implements "reliable" piped
    logs in mod_log_config. Where reliable means that if the logging child dies
    for whatever reason, apache will recover and respawn it without having to
    restart the entire server. Furthermore if the logging child becomes "stuck"
    and isn't reading its pipe frequently enough apache will also restart it.
    This opens up more opportunities for log rotation, hit filtering real-time
    splitting of multiple vhosts into separate logs, and asynchronous DNS
    resolving on the fly.

* Virtual Hosts
    Apache is able to manage websites using a single ip address. This can be
    done by creating multiple virtual hosts on the same web server. We can
configure virtual hosts for regular websites in the main apache configuration
file /etc/httd/conf/httpd.conf.

Updating a Home Page

1. after installing the apache webserver start the apache server with the default
   configuration.
2. Copy any html file to /var/www/html/index.html
3. Make any changes to the html file if you want your own information on it.
4. Using the web browser such as Mozilla firefox Browser to connect to the
      localhost and check whether the same html page is reflected.

Virtual Host

1. mkdir -p /var/www/virtual
2. vim /etc/httpd/conf/httpd.conf

       VirtualHost www.example.com:80
        ServerAdmin root@IP Address
        DocumentRoot /var/www/virtual
        ServerName www.example.com
        ErrorLog logs/ error_log
        Customlog logs/ access_log common
      VirtualHost

3. Line no. 971 Name VirtualHost IPAddress:80
4. Service httpd restart
5. chkconfig httpd on

RHCT & RHCE Exam Solution

2012-02-16T11:57:00.003+05:30

RHCT & RHCE Exam Solution

Q1. Create the following users, groups and group membership:

# groupadd sysusers
# useradd -G sysusers andrew; passwd andrew
# useradd -G sysusers susan; passwd susan
# useradd -s /sbin/nologin brad; passwd brad

Q2. Create a collaborative directory /shared/sysusers with following
       characteristics:

# mkdir -p /shared/sysusers
# chgrp sysusers /shared/sysusers
# chmod 2770 /shared/sysusers

Q3. Install appropriate kernel update from
       ftp://server1.example.com/pub/updates.

-   First download kernel from server using ftp.
# ftp 192.168.1.254
# mget kernel-* name
# rpm -ivh -aid -force kernel-*
-    Check the /etc/grub.conf in that file what is the default=0 is there or not.

Q4. Enable IP forwarding on your machine.

# vim /etc/sysctl.conf
     (line no. 7 ) net.ipv4.ip_forward = 1
# sysctl -p
# service network restart

Q5. The user andrew must configure a cron job that runs daily at 15:25 local
       time and executes "/bin/echo hello".

# crontab -eu andrew
     25 15 * * * /bin/echo "hello"
# service crond restart
# chkconfig crond on

Q6. Bind to the NIS domain RHCE provided by 192.168.1.254 for usre
       authentication.
# authconfig-tui
    select user NIS
# ypcat passwd
# vim /etc/auto.master
     /rhome/stationX    /etc/auto.misc
# vim /etc/auto.misc
     -rw,soft,intr      192.168.1.254:/rhome/nisuserX
# service autofs restart
# chkconfig autofs on

Q7. Copy the file /etc/fstab to /var/tmp configure the permission of /var/tmp/fstab

# cp -prf /etc/fstab     /var/tmp
# setfacl -m u:andrew:rw /var/tmp/fstab
# setfacl -m u:susan:--- /var/tmp/fstab
# getfacl /var/tmp/fstab

Q8. Configure SSH access as follows.

# yum install openssh*
# vim /etc/ssh/sshd_config
     allowusers susan
# service sshd restart
# chkconfig sshd on
# iptables -I INPUT -s 192.168.0.0/255.255.255.0 -d 192.168.0.X -p tcp --dport
     22 -j REJECT

Q9. Configure POP3 email on your system according to these criteria

# yum install sendmail*
# yum install dovecot*
# vim /etc/mail/sendmail.mc
   ( line no. 116) dnl # DAEMON_OPTIONS ('port-smtp,addr-
     127.0.0.1,Name=MTA') dnl
# vim /etc/aliases
   brad: brad
# vim /etc/dovecot.conf
   Uncomment line no. 17
# service sendmail restart
# service dovecot restart
# chkconfig sendmail on
# chkconfig dovecot on
# iptables -I INPUT -s 192.168.0.0/255.255.0.0 -d 192.168.0.X -p tcp -dport 110
-j REJECT

Q10. Configure FTP access on your system

# yum install vsftp*
# vim /etc/vsftpd/vsftpd.conf
# service vsftpd restart
# chkconfig vsftpd on
# iptables -I INPUT -s 192.168.0.0/255.255.255.0 -d 192.168.0.X -p tcp -dport 21
     -j REJECT

Q11. Share the /shared directory via SMB

# yum install samba* -y
# vim /etc/samba/smb.conf
    line 18: workgroup = SMBGROUP
    line 41: hosts allow 192.168.0.0
    go to bottom of the file and copy last 8 lines and make them uncomment
    [shared]
    comment                 = %m's stuff
    path                        = /shared
    valid users              = susan
    public                      = no
    writable                  = no
    printable                 = no
    create mask            = 0765
    browseable             = yes
# service smb restart
# chkconfigg smb on
# smbpasswd -a susan
# smbclient //192.168.0.X/shared -U susan
                      own pc IP address
# chcon - R -t public_contect_t /shared

Q12. Implement a web server for the site http://stationX.example.com

First download the index page from
ftp://server1.example.com/pub/rhce/station.html
# yum install http*
# cp -rf stationX.html /var/www/html
# cd /var/www/html
# mv stationX.html index.html
# vim /etc/httpd/conf/http.conf
     250   ServerAdmin    root@stationX
   264 ServerName stationX.example.com:80

The bottom of the configuration and copy last line and configure

ServerAdmin root@stationX
DocumentRoot /var/www/html
ServerName stationX.example.com
ErrorLog logs/ com-error_log
Customlog logs/ access_log common

Q13. Export your /shred directory via NFS to example.com domain only

# yum install portmap*
# yum install nfs*
# vim /etc/exports
   /shred    *.192.168.0.0/255.255.255.0(ro,sync)
# service portmap restart
# service nfs restart
# chkconfig portmap on
# chkconfig nfs on

Q14. Configure an email alias for your MTA such that mail send to acctmgr
   is received by the local user andrew

# vim /etc/aliases
   acctmgr:    andrew
# newaliases
# service sendmail restart
# service dovecot restart

Q15. Configure SMTP mail service

# vim /etc/mail/access
     Insert Connect:0.0.0.0/0.0.0.0     RELAY
# service sendmail restart
# service dovecot restart
# chkconfig sendmail on
# chkconfig dovecot on

ADDITIONAL RCHE QUES ANS.

Q1. Implement a web proxy server bound to port 8080

# yum install squid*
# vim /etc/squid/squid.conf
     Line no. 73 http_port 8080
     Line no. 2410 acl mynet src 192.168.0.0/255.255.255.0
     http_access allow mynet
# service squid restart
# chkconfig squid on

Q2. Extend you web server to include a virtual host for site
       http://wwwX.example.com

# mkdir -p /var/www/virtual
# vim /etc/httpd/conf/httpd.conf
     Once again copy last line and configure for virtual host

     ServerAdmin root@stationX
     DocumentRoot /var/www/virtual
     ServerName wwwX.example.com
     ErrorLog logs/ access_log common

# line no. 971 NameVirtualHost 192.168.0.X:80
# service httpd restart
# chkconfig httpd on
# firefox
   wwwX.example.com

RHCT & RHCE

2012-02-15T17:46:00.002+05:30

Red Hat Certified Technician and Red Hat Certified Engineer ( RHCT & RHCE)

Exam Question and Solution

RHCT

Q1. Your system has a new 100MB physical partition mounted under      /mnt/new with a 100MB ext3 filesystem.
Note:because partition sizes are seldom exactly what is specified when they are created, anything within the range of 90 to 110MB is acceptable.

Q2. Create the following users,groups and group memberships:

-   A group named sysusers.
- A user andrew who belongs to sysusers as a secondary group.
- A user susan who also belongs to sysusers as a secondary group.
- A user brad who does not have access to an interactive shell on the    system, and who is not a member of sysusers.
- andrew, susan and brad should all have th password of password.

Q3. Create a collaborative directory /shared/sysusers with the following characteristics.

- Group ownership of /shared/sysusers is sysusers.
- The directory should be readable, writable and accessible to member   of sysusers, but not to any other user.
( it is understood that root has access to all o,less and directories on the system.)
- Files crated in /shared/sysusers automatically have group ownership set to the sysusers group.

Q5. Set SELinux running in the Enforcing mode.

Q6. Enable IP forwarding on your machine.

Q7. Install th appropriate kernel update from
     ftp://server1.example.com/pub/update. the following criteria must also be met:
- The updated kernel is the default kernel when the system is rebooted
- The original kernel remains available and bootable on the system .

Q8. The user andrew must configure a cron job that runs daily at 15:25 local time and ececutes
- /bin/echo hello

Q9. Bind to the NFS domain RHCE provided by 192.168.1.254 for user authentication.
Note the following:
- nisuserx should be able to log into your system, where x is your station number.
- but will not have a home directory untilll you have completed the autofs requirement below.
- All NFS users have a password of password

Q10. Configure autofs to automount the home directories of NIS users.

Note the following:
- server1.example.com (192.168.1.254) NFS-exports /rhome/stationX to your system where X is your station Number.
nisuserX's home directory is
server1.example.com:/rhome/stationX/nisuserX
- nisuserX's home directory should be automounted locally beneath /rhome as /rhome/nisuserX
- Home directories must be writable by thier users.
- While you are able to log in as any of the users nisuser1 through       nisuser20, the only home.
directory that is accessible from your system is nisuserX.

Q11. Copy the file /etc/fstab to /var/tmp. Configure the permissions of /var/tmp/fstab so that:

- The file /var/tmp/fstab is owned by the root user.
- The file /var/tmp/fstab belongs to the group root.
- The file /var/tmp/fstab should not be executable by anyone.
- The user andrew is able to read and write /var/tmp/fastab.
- The user susan can neither write nor rad /var/tmp/fstab.
- All other users ( current or future ) have the ability to read /var/tmp/fstab.

Q12. Configure your system so that it is an NTP client of server1.example.com.

Q13. Set up the default local print queue to forward jobs to the IPP ( CUPS ) print queue stationX on server1.example.com,
- Where X is your station number. Configure this printer as a "Generic - test - only " print queue.
Note: The queue stationX on server1 dump print jobs into the file
http://server1.example.com:631/printers/stationX.
- This file can be examined to confirm that you have configured the print queue correctly.

RHCE Requirement

Q1. Resize the lvm lv00 up to 100 MB.
Q2. Implement user quota according to following criteria.
- The user neo should be able to run the command
- dd if = /dev/zero of=/home/neo/somefile bs=1024k count=30
- and should not be able to run the command
- dd if=/dev/zero of=/home/neo/somefile bs=1024k count=70

Q3. Configure SSH access as follows:
- susan has remote SSH access to your not have access to your machine from with in example.com.
- Clients within my133t.org should not have access to ssh on your system.

Q4. Configure POP3 email on your system according to these criteria;
- brad must be able to retrieve email from your machine using POP3 from
within example.com
- Client within the my133t.org domain should not have access to your POP3 services.

Q5. Configure FTP access on your system:
- Clients within the example.com domain should have anonymous FTP access
   to your machine.
- Clients outside example.com should not have access to your FTP services .

Q6. Share the /share directory via SMB:
- Your SMB server must be a member of the SMBGROUP workgroup
- The share's name must shared.
- Theshared share must be available to example.com domain clients only.
- Theshared share must be browseable.
- susan must have read access to the share, authenticating with the sane password password, if necessary.

Q7. Implement a web server for the site http://stationX.example.com, then
   perform the following steps:
- Download ftp://server1.example.com/pub/rhce/station.html
- Rename the downloaded file to index.html
- Copy this index.html to the DocumentRoot of your web server.
- Do not nake any modification to the content of index.html

Q8. Export your /shared directory via NFS to the example.com domain only.

Q9. Configure an email alias for your MTA such that mail sent to acctmgr is received by the local user andrew.

Q10. Configure SMTP mail services according to the following requirements:
- Your mail server should accept mail from remote hosts and localhsot.
- susam must be able to receive mail from remote hosts.
- Mail delivered to susan should spool into the default mail spool for susam,
   /var/spool/mail/susan.

Additional RHCE Requirements

Perform any two of the following steps.

Completion of more than two will not result in extra credit.
If time allows, you may wish to complete more than the minimum just in case one of your tasks does not meet our specio,cations.
Please note that these additional items are part of your RHCE-specific score.

Q1. Povide SSL-encapsulated IMAP access ( IMAPS ) :
- IMAPS must be available to bard from example.com
- IMAPS must not be available to other networks or domains.
- The SSL certion,cate for the IMAPS server must be created as follows.
-   Use the default for country, state, locality and organization name.
-   Set organization unit to GLS.
-   Set common name to stationX.example.com
-   Set Email address to root@stationX.example.com

Q2. Implement a web proxy server bound to port 8080.
-   Clients within example.com should have access to your proxy server.
-   Clients outside of example.com should not have access to your proxy server.

Q3. Extend your web server to include a virtual host for the site
       http://wwwX.example.com/, where X is

- Your station number, then perform the following steps:
- Set the DocumentRoot to /var/www/virtual
- Download ftp://server1.example.com/pub/rhce/www.html
- Rename the downloaded file to index.html
- Place this index.html in the documentsroot of the virtual host
- Do not make any modification to the content of index.html
- Ensure that susan is able to create content in /var/www/virtual

Note: The original web site http://stationX.example.com must still be accessable.
DNS resolution for the hostname wwwX.example.com is already provided by the name server on server1.example.com

Linux Mail Server

2012-02-14T17:13:00.000+05:30

Configuring Linux Mail Server

Configuring postfix & Sendmail.
How postfix & Sendmail works.
Installing postfix & Sendmail.
Starting postfix & sendmail.
How to Restart sendmail & postfix after editing your configuration files.
The /etc/mail/sendmail.mc file.
Configuring DNS for sendmail.
How to configure Linux Sendmail & postfix clients.
Converting from a mail client to a Mail server.
The /etc/mail/relay-domains file.
The /etc/mail/access file.
The /etc/mail/local-host-names file.
Which user should really receive the mail?
Sendmail Masquerading Explained.
Using Sendmail to change the sender's Email Address.
Troubleshooting Sendmail.
Fighting SPAM.
Using Public SPAM Blacklists with Sendmail.
Spamassassin.
A simple PERL script to help stop SPAM.
Configuring your POP Mail Server.
Installing your POP Mail Server.
Starting your POP Mail Server.
How to Configure your windows Mail programs.
Configuring Secure POP Mail.
How to handle overlapping email addresses.
Troubleshooting POP Mail.

MySql,Squid,Network Based Installation and LVM, Quotas

2012-02-14T11:13:00.002+05:30

Controlling Web Usage with Squid

Download and Install the squid package.
The /etc/squid/squid.conf file.
Configuring web browsers to use your squid server.
How to get squid started.
Squid and Firewalls.
squid Disk usage.
Troubleshooting squid.
Other squid capabilities.

Basic MySql Configuration

Installing MySQL.
Starting MySQL.
A common Fedora MySQL startup error.
The location of MySQL Databases.
Creating a MySQL "root" Account.
Accessing the MySQL command line.
Creating and Deleting MySQL Databases.
Recovering your MySQL Root password.
MySQL granting privileges to users.
MySQL database Backup.
MySQL database restoration.
Very Basic MySQL Network Security.

Networking Based Linux Installation

Setting up th installation server.
Creating boot diskettes.
The Networking Installation.
Troubleshooting the network installation.
Automating installation with RadHat Kickstart.

LVM (Logical Volume Manager )

Expanding Linux Partitions with LVM.
LVM Terminologies.
Configuring LVM Devices.

Managing Disk Usage with Quotas

Setting up Quotas.
Other Quota Topics.

SSH, DNS, Apache and NFS server

2012-02-14T10:56:00.002+05:30

Secure Remote Logins & File Copying

Using Secure Shell as a replacement for telnet.
Testing to see if SSH if running.
The /etc/ssh/sshd_config file.
Using SSH to login to a remote machine.
What you should expect to see when you log in.
Deactivating telnet once SSH is installed.
Using SCP as a more secure replacement for FTP.
Copying files using SCP without a password.

Configuring DNS

What is DNS?
What is BIND?
How DNS is critical to web hosting.
When to use a DNS caching name server.
When to use a regular DNS server.
How to Download & install the BIND packages.
How to get Bind started.
Configuring a caching name server.
configure a regular name server.

Web Hosting with the Apache Web Server

Download & Install the Apache package.
How to get Apache started.
Configuring DNS for Apache.
General configuration steps.
File Permission and Apache.
Virtual Hosting- Single IP Address - Many sites.
Apache Running on a server behind a firewell.
How to protect web page Directories with passwords.

Remote Disk Access with NFS

Installing NFS.
How to get NFS started.
The /etc/exports file.
Activating modifications the exports file.
NFS and DNS.
Configuring the NFS client.
Other NFS considerations.

FTP Server

2012-02-13T17:27:00.002+05:30

Configuring a Linux FTP Srever

FTP Overview.
Problem with FTP and firewalls.
How to Download and Install the VSFTP Package.
How to get VSFTP started.
Testing to see if VSFTP is running.
What is Anonymous FTP?
The /etc/vsftpd.conf file.
How to configure VSFTPD to run with authenticated logins.

Secure Remote Logins & File Copying

Using Secure Shell as a replacement for Telnet.
Testing to see if SSH is running.
The /etc/ssh/sshd_config file.
Using SSH to Login to a Remote Machine.
What you should expect to see when you log in.
Deactivating telnet once SSH is installed.
Using SCP as a more secure replacement for FTP.
copying files using SCP without a password.

Configuring DNS

What is DNS?
What is Bind?
How DNS is Critical to web Hosing.
When to use DNS Caching Name Server.
When to use a regular DNS server.
How to download & install the bind package.
How to get BIND started.
Configuring A Caching Name Server.
Configuring A Regular Name Server.

Web Hosing with the Apache Web Server

Download & Install the apache Package.
How to get Apache started.
Configuring DNS for apache.
General configuration steps.
File Permissions And Apache.
Virtual Hosting - Single IP Address - Many Sites.
Apache Running on a server Behind a firewall.
How to protect web page Directories with passwords.

Samba Server

2012-02-13T17:14:00.004+05:30

Configuring Samba Server

How to install Samba packages.
How to start Samba.
The Samba Configuration file.
How SWAT makes Samba Simpler.
Creating A starter configuration.
Fine tuning the configuration.

Sharing Resources with Samba

Adding A printer to a Samba PDC.
Creating Group shares in SAMBA.
Windows Drive sharing with your SAMBA Server.

Linux Wireless Networking

Wireless Linux compatible NICs.
Common Wireless Networking Terms.
Networking with linux wireless-Tools.
Configuring 802.11g with linux incompatible NICs ( with an NDIS wrapper exam).
Compiling ndiswrapper.
Networking with linux-WLAN.
Linux-WLAN Preparation.
Installing the linux-WLAN Drivers.
Post installation Steps.
Linux-WLAN Encryption for security.
Troubleshooting your Wireless LAN.
Wireless networking in businesses.