CCNA MCITP RHCE

Advance File permissions

noreply@blogger.com (Anonymous) — Mon, 03 Dec 2012 15:38:00 +0000

Advance File permissions

In addition to the basic permissions discussed above, there are also three bits of information defined for files in Linux:
SUID or setuid: change user ID on execution. If setuid bit is set, when the file will be executed by a user, the process will have the same rights as the owner of the file being executed.

SGID or setgid: change group ID on execution. Same as above, but inherits rights of the group of the owner of the file on execution. For directories it also may mean that when a new file is created in the directory it will inherit the group of the directory (and not of the user who created the file).
Sticky bit: It was used to trigger process to "stick" in memory after it is finished, now this usage is obsolete. Currently its use is system dependent and it is mostly used to suppress deletion of the files that belong to other users in the folder where you have "write" access to.

Numeric representation
Octal digit Binary value Meaning
0 000 setuid, setgid, sticky bits are cleared
1 001 sticky bit is set
2 010 setgid bit is set
3 011 setgid and sticky bits are set
4 100 setuid bit is set
5 101 setuid and sticky bits are set
6 110 setuid and setgid bits are set
7 111 setuid, setgid, sticky bits are set
Textual representation
SUID, If set, then replaces "x" in the owner permissions to "s", if owner has execute permissions, or to "S" otherwise.
Examples:
-rws------ both owner execute and SUID are set
-r-S------ SUID is set, but owner execute is not set

SGID, If set, then replaces "x" in the group permissions to "s", if group has execute permissions, or to "S" otherwise.
Examples:
-rwxrws--- both group execute and SGID are set
-rwxr-S--- SGID is set, but group execute is not set
Sticky, If set, then replaces "x" in the others permissions to "t", if others have execute permissions, or to "T" otherwise.
Examples:
-rwxrwxrwt both others execute and sticky bit are set
-rwxrwxr-T sticky bit is set, but others execute is not set
Setting the sticky bit on a directory : chmod +t
Setting the SGID attribute on a directory : chmod g+s
If the SGID (Set Group Identification) attribute is set on a directory, files created in that directory inherit its group ownership. If the SGID is not set the file's group ownership corresponds to the user's default group.
In order to set the SGID on a directory or to remove it, use the following commands:
# chmod g+s directory
# chmod g-s directory
When set, the SGID attribute is represented by the letter "s" which replaces the "x" in the group permissions:
# ls -l directory
drwxrwsr-x 10 raju student 4096 2012-12-05 12:50 directory
Setting SUID and SGID attributes on executable files : chmod u+s, chmod g+s
By default, when a user executes a file, the process which results in this execution has the same permissions as those of the user. In fact, the process inherits his default group and user identification.
If you set the SUID attribute on an executable file, the process resulting in its execution doesn't use the user's identification but the user identification of the file owner.
By setting SUID and SGID attributes the owner makes it possible for other users to execute the file as if they were him or members of his default group.
The SUID and GUID are represented by a "s" which replaces the "x" character respectively in the user and group permissions:

# chmod u+s directory
# ls -l
drwxrwsr-x 10 raju student 4096 2012-12-05 12:50 directory

# chmod u-s directory

# chmod g+s directory
# ls -l
-rwxrwsrwx 10 raju student 4096 2012-12-05 12:50 directory

Routing Information Protocol (RIP)

noreply@blogger.com (Anonymous) — Sat, 01 Dec 2012 14:01:00 +0000

Routing Information Protocol (RIP)

The Routing Information Protocol (RIP) is a simple, effective routing protocol for small- to medium-sized networks.

By using a routing protocol, routers automatically share route information, reducing the amount of administration required for maintaining routes between networks

Metric used by rip protocol was HOP count.

RIP is implemented on top of the User Datagram Protocol as its transport protocol. It is assigned the reserved port number 520.

Maximum hop counts for this protocol is 15 and maximum routers are 16.

Administrative distance of rip protocol is 120

Updates are broadcasted via 255.255.255.255

Each update contains maximum of 25 routers

RIP Timers

RIP uses four different kinds of timers to regulate its performance:

Route update timer

Sets the interval (typically 30 seconds) between periodic routing updates in which the router sends a complete copy of its routing table out to all neighbors.

Route invalid timer

Determines the length of time that must elapse (180 seconds) before a router determines that a route has become invalid. It will come to this conclusion if it hasn’t heard any updates about a particular route for that period. When that happens, the router will send out updates to all its neighbors letting them know that the route is invalid.

Holddown timer

This sets the amount of time during which routing information is suppressed. Routes will enter into the holddown state when an update packet is received that indicated the route is unreachable. This continues either until an update packet is received with a better metric or until the holddown timer expires. The default is 180 seconds.

Route flush timer

Sets the time between a route becoming invalid and its removal from the routing table (240 seconds). Before it's removed from the table, the router notifies its neighbors of that route's impending failure. The value of the route invalid timer must be less than that of the route flush timer. This gives the router enough time to tell its neighbors about the invalid route before the local routing table is updated.

Versions

IP RIP (Routing Information Protocol) comes in two different versions: 1 and 2. Version 1 is a distance vector protocol (RFC 1058) and Version 2 is a hybrid protocol (RFCs 1721 and 1722).

Routing Information Protocol Version 1 (RIPv1)

RIPv1 uses local broadcasts to share routing information. These updates are periodic in nature, occurring, by default, every 30 seconds. To prevent packets from circling around a loop forever, both versions of RIP solve counting to infinity by placing a hop count limit of 15 hops on packets. Any packet that reaches the sixteenth hop will be dropped. RIPv1 is a classful protocol. RIP supports up to six equal-cost paths to a single destination. Equal-cost path are the paths where the metric is same (Hop count).

Routing Information Protocol (RIPv2)

RIPv2 is a distance vector protocol with routing enhancements built into it, and it is based on RIPV1. Therefore, it is commonly called a hybrid protocol.

RIPv2 uses multicasts instead of broadcasts. RIPv2 supports triggered updates. when a change occurs, a RIPv2 router will immediately propagate its routing information to its connected neighbours. RIPv2 is a classless protocol and it supports variable-length subnet masking (VLSM).

Both RIPv1 and RIPv2 uses hop count as the metric.

Differences between RIPv1 and RIPv2

RIPv1

•Supports only classful routing (Does not support VLSM).

•No authentication.

•RIPv1 uses Broadcast.

RIPv2

•Supports classless routing (Supports VLSM). RIPv2 incorporates the addition of the network mask in the update to allow classless routing advertisements.

•Authentication is available.

•RIPv2 uses multi-cast instead of broadcast. multicast communication reduces the burden on the network devices that do not need to listen to RIP updates.

Useful command for RIP

Router(config)#router rip Enables RIP as a routing protocol

Router(config-router)#network IP address

IP is the network number of the directly connected network you want to advertise.

Router(config)#no router rip Turns off the RIP routing process

Router(config-router)#no network Ipaddress

Removes network IP from the RIP routing process.

Router(config-router)#version 2 RIP will now send and receive RIPv2 packets globally.

Router(config-router)#version 1 RIP will now send and receive RIPv1 packets only

Router(config-router)#no auto-summary RIPv2 summarizes networks at the classful boundary. This command turns autosummarization off.

Router(config-router)#passive-interface s0/0/0 RIP updates will not be sent out this interface.

Router(config-router)#no ip split-horizon Turns off split horizon (on by default).

Router(config-router)#ip split-horizon Re-enables split horizon

Router(config-router)#timers basic 30 90 180 270 360

Changes timers in RIP: 30 = Update timer (in seconds) 90 = Invalid timer (in seconds) 180 = Hold-down timer (in seconds) 270 = Flush timer (in seconds) 360 = Sleep time (in milliseconds)

Router#debug ip rip Displays all RIP activity in real time

Router#show ip rip database Displays contents of the RIP database

Configuration

To configure any routing protocol, use the following three steps:

1. Enable IP routing if it is not already enabled (use the ip routing command). By default, IP

routing is already enabled, so this step is rarely required.

2. Switch to router configuration mode (use the router command, followed by the routing

protocol you want to configure).

3. Identify the networks that will participate in dynamic routing (use the network command,

followed by the address of a network to which the router is directly connected). This

identifies the interfaces that will share and process received routing updates.

4. Configure any additional parameters based on the routing protocol.

Routing Information Protocol (RIP) can be configured in a router using the following IOS commands. The "version 2" IOS command specifies that we are using RIPv2.

Router>enable

Router#configure terminal

Router(config)# router rip

Router(config-router)# version 2

Router(config-router)# network network_id

Linux network commands

noreply@blogger.com (Anonymous) — Thu, 29 Nov 2012 14:04:00 +0000

Linux Network Configuration and Troubleshooting Commands

Computers are connected in a network to exchange information or resources each other. Two or more computer connected through network media called computer network. There are number of network devices or media are involved to form computer network. Computer loaded with Linux Operating System can also be a part of network whether it is small or large network by its multitasking and multiuser natures. Maintaining of system and network up and running is a task of System / Network Administrator’s job. In this article we are going to review frequently used network configuration and troubleshoot commands in Linux.

Linux Network Configuration and Troubleshooting Commands

1. ifconfig

ifconfig (interface configurator) command is use to initialize an interface, assign IP Address to interface and enable or disable interface on demand. With this command you can view IP Address and Hardware / MAC address assign to interface and also MTU (Maximum transmission unit) size.

# ifconfig

eth0 Link encap:Ethernet HWaddr 00:0C:29:28:FD:4C

inet addr:192.168.50.2 Bcast:192.168.50.255 Mask:255.255.255.0

inet6 addr: fe80::20c:29ff:fe28:fd4c/64 Scope:Link

UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

RX packets:6093 errors:0 dropped:0 overruns:0 frame:0

TX packets:4824 errors:0 dropped:0 overruns:0 carrier:0

collisions:0 txqueuelen:1000

RX bytes:6125302 (5.8 MiB) TX bytes:536966 (524.3 KiB)

Interrupt:18 Base address:0x2000

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:8 errors:0 dropped:0 overruns:0 frame:0

TX packets:8 errors:0 dropped:0 overruns:0 carrier:0

collisions:0 txqueuelen:0

RX bytes:480 (480.0 b) TX bytes:480 (480.0 b)

ifconfig with interface (eth0) command only shows specific interface details like IP Address, MAC Address etc. with -a options will display all available interface details if it is disable also.

# ifconfig eth0

eth0 Link encap:Ethernet HWaddr 00:0C:29:28:FD:4C

inet addr:192.168.50.2 Bcast:192.168.50.255 Mask:255.255.255.0

inet6 addr: fe80::20c:29ff:fe28:fd4c/64 Scope:Link

UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

RX packets:6119 errors:0 dropped:0 overruns:0 frame:0

TX packets:4841 errors:0 dropped:0 overruns:0 carrier:0

collisions:0 txqueuelen:1000

RX bytes:6127464 (5.8 MiB) TX bytes:539648 (527.0 KiB)

Interrupt:18 Base address:0x2000

Assigning IP Address and Gateway

Assigning an IP Address and Gateway to interface on the fly. The setting will be removed in case of system reboot.

# ifconfig eth0 192.168.50.5 netmask 255.255.255.0

Enable or Disable Specific Interface

To enable or disable specific Interface, we use example command as follows.

Enable eth0

# ifup eth0

Disable eth0

# ifdown eth0

Setting MTU Size

By default MTU size is 1500. We can set required MTU size with below command. Replace XXXX with size.

# ifconfig eth0 mtu XXXX

Set Interface in Promiscuous mode

Network interface only received packets belongs to that particular NIC. If you put interface in promiscuous mode it will received all the packets. This is very useful to capture packets and analyze later. For this you may require superuser access.

# ifconfig eth0 - promisc

2. PING Command

PING (Packet INternet Gopher) command is the best way to test connectivity between two nodes. Whether it is Local Area Network (LAN) or Wide Area Network (WAN). Ping use ICMP (Internet Control Message Protocol) to communicate to other devices. You can ping host name of ip address using below command.

# ping 192.168..1

PING 192.168..1 (192.168..1) 56(84) bytes of data.

64 bytes from 192.168..1: icmp_seq=1 ttl=44 time=203 ms

64 bytes from 192.168..1: icmp_seq=2 ttl=44 time=201 ms

64 bytes from 192.168..1: icmp_seq=3 ttl=44 time=201 ms

# ping www.raju.com

PING raju.com (192.168..1) 56(84) bytes of data.

64 bytes from 192.168..1: icmp_seq=1 ttl=47 time=284 ms

64 bytes from 192.168..16: icmp_seq=2 ttl=47 time=287 ms

64 bytes from 192.168..1: icmp_seq=3 ttl=47 time=285 ms

In Linux ping command keep executing until you interrupt. Ping with -c option exit after N number of request (success or error respond).

# ping -c 5 www.raju.com

PING raju.com (50.116.66.136) 56(84) bytes of data.

64 bytes from 192.168..1: icmp_seq=1 ttl=47 time=285 ms

64 bytes from 192.168..1: icmp_seq=2 ttl=47 time=285 ms

64 bytes from 192.168..1: icmp_seq=3 ttl=47 time=285 ms

--- raju.com ping statistics ---

5 packets transmitted, 5 received, 0% packet loss, time 4295ms

rtt min/avg/max/mdev = 285.062/285.324/285.406/0.599 ms

3. TRACEROUTE Command

traceroute is a network troubleshooting utility which shows number of hops taken to reach destination also determine packets traveling path. Below we are tracing route to global DNS server IP Address and able to reach destination also shows path of that packet is traveling.

4. NETSTAT Command

Netstat (Network Statistic) command display connection info, routing table information etc. To displays routing table information use option as -r.

# netstat -r

Kernel IP routing table

Destination Gateway Genmask Flags MSS Window irtt Iface

192.168.50.0 * 255.255.255.0 U 0 0 0 eth0

link-local * 255.255.0.0 U 0 0 0 eth0

default 192.168.50.1 0.0.0.0 UG 0 0 0 eth0

5. DIG Command

Dig (domain information groper) query DNS related information like A Record, CNAME, MX Record etc. This command mainly use to troubleshoot DNS related query.

# dig www.raju.com; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.10.rc1.el6 <<>> www.raju.com

;; global options: +cmd

;; Got answer:

;; ->>HEADER<

6. NSLOOKUP Command

nslookup command also use to find out DNS related query. The following examples shows A Record (IP Address) of tecmint.com.

# nslookup www.raju.com

Server: 4.2.2.2

Address: 4.2.2.2#53

Non-authoritative answer:

www.raju.com canonical name = raju.com.

Name: raju.com

Address: 50.116.66.136

7. ROUTE Command

route command also shows and manipulate ip routing table. To see default routing table in Linux, type the following command.

# route

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

192.168.50.0 * 255.255.255.0 U 0 0 0 eth0

link-local * 255.255.0.0 U 1002 0 0 eth0

default 192.168.50.1 0.0.0.0 UG 0 0 0 eth0

Adding, deleting routes and default Gateway with following commands.

Route Adding

# route add -net 192.168.0.0/24 gw 192.168.0.1

Route Deleting

# route del -net 192.168.0.0/24 gw 192.168.0.1

Adding default Gateway

# route add default gw 192.168.0.1

8. HOST Command

host command to find name to IP or IP to name in IPv4 or IPv6 and also query DNS records.

# host www.google.com

www.google.com has address 173.194.38.180

www.google.com has address 173.194.38.176

www.google.com has address 173.194.38.177

www.google.com has address 173.194.38.178

www.google.com has address 173.194.38.179

www.google.com has IPv6 address 2404:6800:4003:802::1014

Using -t option we can find out DNS Resource Records like CNAME, NS, MX, SOA etc.

# host -t CNAME www.redhat.com

www.redhat.com is an alias for wildcard.redhat.com.edgekey.net.

9. ARP Command

ARP (Address Resolution Protocol) is useful to view / add the contents of the kernel’s ARP tables. To see default table use the command as.

# arp -e

Address HWtype HWaddress Flags Mask Iface

192.168.50.1 ether 00:50:56:c0:00:08 C eth0

10. ETHTOOL Command

ethtool is a replacement of mii-tool. It is to view, setting speed and duplex of your Network Interface Card (NIC). You can set duplex permanently in /etc/sysconfig/network-scripts/ifcfg-eth0 with ETHTOOL_OPTS variable.

# ethtool eth0

Settings for eth0:

Current message level: 0x00000007 (7)

Link detected: yes

11. IWCONFIG Command

iwconfig command in Linux is use to configure a wireless network interface. You can see and set the basic Wi-Fi details like SSID channel and encryption. You can refer man page of iwconfig to know more.

# iwconfig [interface]

12. HOSTNAME Command

hostname is to identify in a network. Execute hostname command to see the hostname of your box. You can set hostname permanently in /etc/sysconfig/network. Need to reboot box once set a proper hostname.

# hostname

raju.com

13. GUI tool system-config-network

Type system-config-network in command prompt to configure network setting and you will get nice Graphical User Interface (GUI) which may also use to configure IP Address, Gateway, DNS etc. as shown below image.

# system-config-network

File/Directory Basic commands

noreply@blogger.com (Anonymous) — Wed, 28 Nov 2012 14:31:00 +0000

File/Directory Basic commands

cat command
     cat linux command concatenates files and print it on the standard output.
Syntax  The Syntax is

cat [options] [Filenames]

Options

-A	Show all.
-b	Omits line numbers for blank space in the output.
-e	A $ character will be printed at the end of each line prior to a new line.
-E	Displays a $ (dollar sign) at the end of each line.
-n	Line numbers for all the output lines.
-s	If the output has multiple empty lines it replaces it with one empty line.
-T	Displays the tab characters in the output.
-v	Non-printing characters (with the exception of tabs, new-lines and form-feeds) are printed visibly.

Example

1. To Create a new file:

cat > file1.txt

This command creates a new file file1.txt. After typing into the file press ctrl+d (^d) simultaneously to end the file.

2. To Append data into the file:

cat >> file1.txt

To append data into the same file use append operator >> to write into the file, else the file will be overwritten (i.e., all of its contents will be erased).

3. To display a file:

cat file1.txt

This command displays the data in the file.

4. To concatenate several files and display:

cat file1.txt file2.txt

The above cat command will concatenate the two files (file1.txt and file2.txt) and it will display the output in the screen. Sometimes the output may not fit the monitor screen. In such situation you can print those files in a new file or display the file using less command.

cat file1.txt file2.txt | less

5. To concatenate several files and to transfer the output to another file.

cat file1.txt file2.txt > file3.txt

In the above example the output is redirected to new file file3.txt. The cat command will create new file file3.txt and store the concatenated output into file3.txt.

cd command

   cd command is used to change the directory.

SYNTAX:
  The Syntax is
     cd [directory | ~ | ./ | ../ | - ]
Options

-L	Use the physical directory structure.
-P	Forces symbolic links.

Example

1. cd /home/data

This command will take you to /home/data

2. cd ..

This will change to the parent-directory from the current working directory/sub-directory.

3. cd ~

This command will move to the user's home directory which is "/home/username".

ls command

ls command lists the files and directories under current working directory.
Syntax
The Syntax is
ls [options] [Filenames]

Options

-l	Lists all the files, directories and their mode, Number of links, owner of the file, file size, Modified date and time and filename.
-t	Lists in order of last modification time.
-a	Lists all entries including hidden files.
-d	Lists directory files instead of contents.
-p	Puts slash at the end of each directories.
-u	List in order of last access time.
-i	Display inode information.
-ltr	List files order by date.
-lSr	List files order by file size.

Example

Display root directory contents:

ls /

lists the contents of root directory.

1. Display hidden files and directories:

ls -a

lists all entries including hidden files and directories.

cp command
     cp command copy files from one location to another. If the destination is an existing file, then the file is overwritten; if the destination is an existing directory, the file is copied into the directory (the directory is not overwritten).
Syntax
  The Syntax is
     cp [options]... sourcefile destination file
     cp [options]... sourcedir destinationdir
Options

-a	same as -dpR.
--backup[=CONTROL]	make a backup of each existing destination file
-b	like --backup but does not accept an argument.
-f	if an existing destination file cannot be opened, remove it and try again.
-p	same as --preserve=mode,ownership,timestamps.
--preserve[=ATTR_LIST]	preserve the specified attributes (default: mode,ownership,timestamps) and security contexts, if possible additional attributes: links, all.
--no-preserve=ATTR_LIST	don't preserve the specified attribute.
--parents	append source path to DIRECTORY.

Example

1. Copy two files:

cp file1 file2

The above cp command copies the content of file1.php to file2.php.

2. To backup the copied file:

cp -b file1.docl file2.doc

Backup of file1.docl will be created with '~' symbol as file1.doc2~.

3. Copy folder and subfolders:

cp -R data data2

The above cp command copy the folder and subfolders from data to data2

mv command

     mv command which is short for move. It is used to move/rename file from one directory to another. mv command is different from cp command as it completely removes the file from the source and moves to the directory specified, where cp command just copies the content from one file to another.
Syntax
  The Syntax is
     mv [-f] [-i] oldname newname
Options

-f	mv -f will move the file(s) without prompting even if it is writing over an existing target.
-i	Prompts before overwriting another file.

Example

1. To Rename / Move a file:

mv file1.txt file2.txt

This command renames file1.txt as file2.txt

2. To move a directory

mv data tmp

In the above line mv command moves all the files, directories and sub-directories from data folder/directory to tmp directory if the tmp directory already exists. If there is no tmp directory it rename's the data directory as tmp directory.

3. To Move multiple files/More files into another directory

mv file1.txt tmp/file2.txt newdir

This command moves the files file1.txt from the current directory and file2.txt from the tmp folder/directory to newdir.

rm command
rm linux command is used to remove/delete the file from the directory.
Syntax

The Syntax is
rm [options..] [file | directory]
Options

-f	Remove all files in a directory without prompting the user.
-i	Interactive. With this option, rm prompts for confirmation before removing any files.
-r (or) -R	Recursively remove directories and subdirectories in the argument list. The directory will be emptied of files and removed. The user is normally prompted for removal of any write-protected files which the directory contains.

Example

1. To Remove / Delete a file:

rm file1.txt

Here rm command will remove/delete the file file1.txt.

2. To delete a directory tree:

rm -ir tmp

This rm command recursively removes the contents of all subdirectories of the tmp directory, prompting you regarding the removal of each file, and then removes the tmp directory itself.

3. To remove more files at once

rm file1.txt file2.txt

rm command removes file1.txt and file2.txt files at the same time.

mkdir command

     mkdir command is used to create one or more directories.
Syntax
  The Syntax is
     mkdir [options] [directoriename]
Options

-m	Set the access mode for the new directories.
-P	Create multiple directories
-v	Print help message for each directory created.

Example

1. Create directory:

mkdir data

The above command is used to create the directory 'data'.

2. Create directory and set permissions:

mkdir -m 666 data

The above command is used to create the directory 'data' and set the read and write permission.

Basic commands

noreply@blogger.com (Anonymous) — Wed, 28 Nov 2012 13:35:00 +0000

Basic commands

A virtual console is a command line where you can log into and control Linux. As RHEL is a multi terminal operating system, you can log into Linux, even with the same user ID, several times.

There are 7 terminals for Linux. 6 terminals are non - GUI and 1 terminal for GUI access. You can login to each terminal using Alt + Ctrl + F1 , F2, .. F7. Each terminals will request your username and password for login. If you want to use the shell in the graphical interface (GUI), press Alt + F2 and type "konsole". As a user you will have permission to access only your /home/user directory and other directories in it.

pwd command:
pwd - Print Working Directory. pwd command prints the full filename of the current working directory.

Syntax
The Syntax is pwd [options]
Options

-P	The pathname printed will not contain symbolic links.
-L	The pathname printed may contain symbolic links.

Example:

Displays the current working directory.

root@raju~]#pwd

If you are working in home directory then, pwd command displays the current working directory as /home.

who command
      who command can list the names of users currently logged in, their terminal, the time they have been logged in, and the name of the host from which they have logged in.

Syntax
  The Syntax is
     who [options] [file]
Options

am i	Print the username of the invoking user, The 'am' and 'i' must be space separated.
-b	Prints time of last system boot.
-d	print dead processes.
-H	Print column headings above the output.
-i	Include idle time as HOURS:MINUTES. An idle time of . indicates activity within the last minute.
-m	Same as who am i.
-q	Prints only the usernames and the user count/total no of users logged in.
-T,-w	Include user's message status in the output.

cal command:
     cal command is used to display the calendar.
Syntax
  The Syntax is
     cal [options] [month] [year]
Options

-1	Displays single month as output.
-3	Displays prev/current/next month output.
-s	Displays sunday as the first day of the week.
-m	Displays Monday as the first day of the week.
-j	Displays Julian dates (days one-based, numbered from January 1).
-y	Displays a calendar for the current year.

date command
     date command prints the date and time
Syntax  The Syntax is
     date  [options] [+format] [date]
Options

-a	Slowly adjust the time by sss.fff seconds (fff represents fractions of a second). This adjustment can be positive or negative.Only system admin/ super user can adjust the time.
-s date-string	Sets the time and date to the value specfied in the datestring. The datestr may contain the month names, timezones, 'am', 'pm', etc.
-u	Display (or set) the date in Greenwich Mean Time (GMT-universal time).

Format:

%a	Abbreviated weekday(Tue).
%A	Full weekday(Tuesday).
%b	Abbreviated month name(Jan).
%B	Full month name(January).
%c	Country-specific date and time format..
%D	Date in the format %m/%d/%y.
%j	Julian day of year (001-366).
%n	Insert a new line.
%p	String to indicate a.m. or p.m.
%T	Time in the format %H:%M:%S.
%t	Tab space.
%V	Week number in year (01-52); start week on Monday.

Example:

1. date command

date

The above command will print wed Nov 28 10:52:34 IST 2012

2. To use tab space:

date +"Date is %D %t Time is %T"

The above command will remove space and print as
Date is 11/28/12 Time is 10:52:34

3. To set the date,

date -s "11/28/2012 11:37:23"

The above command will print wed Nov 28 11:37:23IST 2012

clear command This command clears the terminal screen.
Syntax

The Syntax isclear
Options

There is no options for clearscreen command.
Example

1. clear

clear command clearscreen like cls command.

2. You can also have alias for this command.

alias c='clear'

c is the alias name for clear command.

hostname command

     hostname specifies the name of the host.
Syntax  The Syntax is
     hostname [-a | -d | -f | -h | -i | -s]
Options

-a	Displays the alias name of the host, if used.
-d	Displays DNS domain name
-f	Displays fully qualified domain name.
-h	Displays help message.
-i	Displays IP address of the host.
-s	Trim domain name from display.

Example

1. hostname command

hostname

The above command will print as raju.com

2. hostname -a

The above command will remove space and print as raju

3. To display DNS domain name

hostname -d

The above command will print as .com

ACLs

noreply@blogger.com (Anonymous) — Tue, 27 Nov 2012 16:45:00 +0000

Access Control Lists (ACLs)

Files and directories have permission sets for the owner of the file, the group associated with the file, and all other users for the system. However, these permission sets have limitations. For example, different permissions cannot be configured for different users. Thus, Access Control Lists (ACLs) were implemented

Mounting File Systems

Before using ACLs for a file or directory, the partition for the file or directory must be mounted with ACL support. If it is a local ext4 file system, it can mounted with the following command:

mount -t ext4 -o acl <device-name><partition>

For example:

mount -t ext4 -o acl /dev/Student/IT

Alternatively, if the partition is listed in the /etc/fstab file, the entry for the partition can include the acl option:

/dev/Student/IT /student ext4 defaults,acl 0 0

Setting Access ACLs

T here are two types of ACLs: access ACLs and default ACLs. An access ACL is the access control list for a specific file or directory. A default ACL can only be associated with a directory; if a file within the directory does not have an access ACL, it uses the rules of the default ACL for the directory. Default ACLs are optional.

ACLs can be configured:

1. Per user

2. Per group

3. Via the effective rights mask

4. For users not in the user group for the file

Configuring ACLs

The setfacl utility sets ACLs for files and directories. Use the -m option to add or modify the ACL of a file or directory:

setfacl -m <rules><files>

Rules (<rules>) must be specified in the following formats. Multiple rules can be specified in the same command if they are separated by commas.

u:<uid> or <username>:<permissions>

Sets the access ACL for a user. T he user name or UID may be specified. T he user may be any

valid user on the system.

g:<gid>or <groupname>:<permissions>

Sets the access ACL for a group. T he group name or GID may be specified. T he group may be

any valid group on the system.

m : <permissions>

Sets the effective rights mask. T he mask is the union of all permissions of the owning group

and all of the user and group entries.

o: <permissions>

Sets the access ACL for users other than the ones in the group for the file.

White space is ignored. Permissions must be a combination of the characters r, w, and x for read, write, and execute.

If a file or directory already has an ACL, and the setfacl command is used, the additional rules are added to the existing ACL or the existing rule is modified.

For example, to give read and write permissions to user raju:

setfacl -m u:raju:rw /file1

T o remove all the permissions for a user, group, or others, use the -x option and do not specify any permissions:

setfacl -x <rules><files>

For example, to remove all permissions from the user with UID 500:

setfacl -x u:500 /file1

Setting Default ACLs

T o set a default ACL, add d: before the rule and specify a directory instead of a file name.

For example, to set the default ACL for the /share/ directory to read and execute for users not in the user group (an access ACL for an individual file can override it):setfacl -m d:o :rx /share

Retrieving ACLs

To determine the existing ACLs for a file or directory, use the getfacl command:

getfacl <filename>

It returns output similar to the following:

# file: file

# owner: raju

# group: student

user::rw

user:koti:r--

group::r--

mask::r--

other::r--

If a directory is specified, and it has a default ACL, the default ACL is also displayed such as:

# file: file

# owner: raju

# group: student

user::rw

user:koti:r--

group::r--

mask::r--

other::r--

default:user::rwx

default:user:raju:rwx

default:group::r-x

default:m ask::rwx

default:other::r-x

Basic file permissions

noreply@blogger.com (Anonymous) — Tue, 27 Nov 2012 13:52:00 +0000

Basic file permissions

Every file on your Linux system, including directories, is owned by a specific user and group. Therefore, file permissions are defined separately for users, groups, and others.

User: The username of the person who owns the file. By default, the user who creates the file will become its owner.

Group: The usergroup that owns the file. All users who belong into the group that owns the file will have the same access permissions to the file.

Other: A user who isn't the owner of the file and doesn't belong in the same group the file does. In other words, if you set a permission for the "other" category, it will affect everyone else by default.

Types of access permissions

There are three types of access permissions on Linux: read, write, and execute. These permissions are defined separately for the file's owner, group and all other users.

Read permission: On a regular file, the read permission bit means the file can be opened and read. On a directory, the read permission means you can list the contents of the directory.

Write permission: On a regular file, this means you can modify the file or write new data to the file. In the case of a directory, the write permission means you can add, remove, and rename files in the directory. This means that if a file has the write permission bit, you are allowed to modify the file's contents, but you're allowed to rename or delete the file only if the permissions of the file's directory allow you to do so.

Execute permission: In the case of a regular file, this means you can execute the file as a program or a shell script.

we can view the access permissions of a file by doing the long directory listing with the ls -l command. This is what a long directory listing might look like:

[roo@raju~]ls -l

drwxr-xr-x 3 raju student 80 2012-11-27 21:37 dir

-rw-r----- 1 raju student 8187 2012-11-25 13:35 file

-rwxr-xr-x 1 raju student 10348 2012-10-30 20:31 otherfile

The very first column,shows the file type and permissions. The second column shows the number of links (directory entries that refer to the file), the third one shows the owner of the file, and the fourth one shows the group the file belongs to. The other columns show the file's size in bytes, date and time of last modification, and the filename.

The first character can be any of these:

d = directory

- = regular file

l = symbolic link

s =Linux domain socket

p = named pipe

c = character device file

b = block device file

The next nine characters show the file's permissions, divided into three groups, each consisting of three characters. The first group of three characters shows the read, write, and execute permissions for user, the owner of the file. The next group shows the read, write, and execute permissions for the group of the file. Similarly, the last group of three characters shows the permissions for other, everyone else. In each group, the first character means the read permission, the second one write permission, and the third one execute permission.

The characters are

r = read permission

w = write permission

x = execute permission

- = no permission

Setting file permissions

We can set file permissions with the chmod command. Both the root user and the file's owner can set file permissions.

chmod has two modes,

Symbolic
Numeric.

Symbolic mode

The symbolic mode option consists of three parts: the user category (owner, group, or other) affected, the function performed, and the permissions affected. For example, if the option is g+x, the executable permission is added for the group.

Numeric mode

The syntax for the chmod command in octal mode is:

chmod octalmode filename

The octalmode option consists of three octal numbers, 0 to 7, that represent a combination of permissions for the file or directory..

Assigned Octal Values for Permissions

Octal Value Permission

4 Read

2 Write

1 Execute

These numbers are combined into one number for each permission set.

Octal Digits for Permission Sets

Octal Value	Permission Sets
7	rwx	421
6	rw-	420
5	r-x	401
4	r--	400
3	-wx	021
2	-w-	020
1	--x	001
0	---	000

You can modify the permissions for each category of users by combining octal numbers. The first octal number defines owner permissions, the second octal number defines group permissions, and the third octal number defines other permissions.

Combined Octal Mode Values and Permissions

Octal Mode	Permissions
644	rw-r--r--
751	rwxr-x--x
775	rwxrwxr-x
777	rwxrwxrwx

Changing Ownership

chown

     chown command is used to change the owner / user of the file or directory. This is an admin command, root user only can change the owner of a file or directory.

Syntax:
  The Syntax is
     chown [options] newowner filename/directoryname

Options:

-R	Change the permission on files that are in the subdirectories of the directory that you are currently in.
-c	Change the permission for each file.
-f	Prevents chown from displaying error messages when it is unable to change the ownership of a file.

chgrp:
     chgrp command is used to change the group of the file or directory. This is an admin command. Root user only can change the group of the file or directory.
Syntax:
  The Syntax is
     chgrp [options] newgroup filename/directoryname
Options:

-R	Change the permission on files that are in the subdirectories of the directory that you are currently in.
-c	Change the permission for each file.
-f	Force. Do not report errors.

Examples

[root@raju]#chmod u+r g+r 0+x textfile

[root@raju]# chmod ug+rwx o+r-- textfile

[root@raju]# chmod 755 textfile

[root@raju]#chown raju:raju textfile

[root@raju]#chgrp koti textfile

OpenSSH

noreply@blogger.com (Anonymous) — Mon, 26 Nov 2012 12:50:00 +0000

OpenSSH

OpenSSH is a free, open source implementation of the SSH (Secure SH ell) protocols. It replaces telnet, ftp, rlogin, rsh, and rcp with secure, encrypted network connectivity tools.

All communications using OpenSSH tools, including passwords, are encrypted. Telnet and ftp use plain text passwords andsend all information unencrypted. T he information can be intercepted, the passwords can be retrieved,and your system could be compromised by an unauthorized person logging in to your system using oneof the intercepted passwords. T he OpenSSH set of utilities should be used whenever possible to avoidthese security problems.

Service Profile

Service: sshd

Package: openssh

Configuration file: /etc/ssh/ssh_config

/etc/ssh/sshd_config

/etc/ssh/ssh_host_dsa_key

/etc/ssh/ssh_host_dsa_key.pub

/etc/ssh/ssh_host_key

/etc/ssh/ssh_host_key.pub

/etc/ssh/ssh_host_rsa_key

/etc/ssh/ssh_host_rsa_key.pub

Daemon:sshd

Objective : To provide secure communications between two systems using a client/server architecture and allows users to log into server host systems remotely.

Install the package

[root@raju~]#yum install openssh* -y

Run the service

[root@raju~]#chkconfig sshd on

[root@raju~]#service sshd restart

To connect to an OpenSSH server from a client machine, you must have the openssh-clients and openssh packages installed on the client machine.

Using the ssh Command

The ssh command is a secure replacement for the rlogin, rsh, and telnet commands. It allows you to log in to a remote machine as well as execute commands on a remote machine.

Logging in to a remote machine with ssh is similar to using telnet. To log in to a remote machine named desktop1.example.com type the following command at a shell prompt:

ssh desktop1.example.com

The first time when you ssh use to a remote machine, you will see a message similar to the following:

The authenticity of host ' desktop1.example.com’ can't be established.

DSA key fingerprint is 94:68:3a:3a:bc:f3:9a:9b:01:5d:b3:07:38:e2:11:0c.

Are you sure you want to continue connecting (yes/no)?

Type yes to continue. This will add the server to your list of known hosts (~/.ssh/known_hosts/) as

seen in the following message:

Warning: Permanently added ‘desktop1.example.com ' (RSA) to the list of known hosts.

Next, you will see a prompt asking for your password for the remote machine. After entering your password, you will be at a shell prompt for the remote machine. If you do not specify a username the username that you are logged in as on the local client machine is passed to the remote machine. If you want to specify a different username, use the following command:

ssh username@desktop1.example.com

You can also use the syntax ssh -l username desktop1.example.com

The ssh command can be used to execute a command on the remote machine without logging in to a shell prompt. The syntax is ssh hostname command.

For example, if you want to execute the command

ls /usr/share/doc on the remote machine desktop1.example.com , type the following command at a

shell prompt:

ssh desktop1.example.com ls /usr/share/doc

After you enter the correct password, the contents of the remote directory /usr/share/doc will be

displayed, and you will return to your local shell prompt.

Using the scp Command

T he scp command can be used to transfer files between machines over a secure, encrypted connection. It is similar to rcp.

The general syntax to transfer a local file to a remote system is as follows:

scp <localfile>username@tohostname:<remotefile>

The <localfile> specifies the source including path to the file, such as /var/log/m aillog. T he

<remotefile> specifies the destination

For the remote system, if you do not have a preceding /, the path will be relative to the home directory of username, typically /hom e/username/.

The general syntax to transfer a remote file to the local system is as follows:

scp username@tohostname:<remotefile><newlocalfile>

T he <remotefile> specifies the source including path, and <newlocalfile> specifies the destination including path.

Multiple files can be specified as the source files. For example, to transfer the contents of the directory downloads/ to an existing directory called uploads/ on the remote machine desktop1.example.com type the following at a shell prompt:

scp downloads/* username@ desktop1.example.com:upl o ads/

Using the sftp Command

The sftp utility can be used to open a secure, interactive FT P session. It is similar to ftp except that it uses a secure, encrypted connection.

The general syntax is sftp username@hostname.com

Once authenticated, you can use a set of commands similar to those used by FT P.

The sftp utility is only available in OpenSSH version 2.5.0p1 and higher.

Generating Key Pairs

If you do not want to enter your password every time you use ssh, scp, or sftp to connect to a remote machine, you can generate an authorization key pair.

Keys must be generated for each user. To generate keys for a user, use the following steps as the userwho wants to connect to remote machines. If you complete the steps as root, only root will be able to use the keys.

To generate an RSA key pair for version 2 of the SSH protocol, follow these steps:

1. Generate an RSA key pair by typing the following at a shell prompt:

2. ssh-keygen -t rsa

3. Generating public/private rsa key pair.

4. Enter file in which to save the key (/home/john/.ssh/id_rsa):

5. Press Enter to confirm the default location (that is, ~/.ssh/id_rsa) for the newly created key.

6. Enter a passphrase, and confirm it by entering it again when prompted to do so. For security reasons, avoid using the same password as you use to log in to your account.

After this, you will be presented with a message similar to this:

Your identification has been saved in /home/john/.ssh/id_rsa.

Your public key has been saved in /home/john/.ssh/id_rsa.pub.

The key fingerprint is:

e7:97:c7:e2:0e:f9:0e:fc:c4:d7:cb:e5:31:11:92:14 john@penguin.example.com

The key's randomart image is:

+--[ RSA 2048]----+

| E. |

| . . |

| o . |

| . .|

| S . . |

| + o o ..|

| * * +oo|

| O +..=|

| o* o.|

+-----------------+

7. Change the permissions of the ~/.ssh/ directory:

8. chmod 755 ~/.ssh

9. Copy the content of ~/.ssh/id_rsa.pub into the ~/.ssh/authorized_keys on the machine to which you want to connect, appending it to its end if the file already exists.

10. Change the permissions of the ~/.ssh/authorized_keys file using the following command:

chmod 644 ~/.ssh/authorized_keys

Swap Partition

noreply@blogger.com (Anonymous) — Mon, 26 Nov 2012 05:47:00 +0000

Swap Partition

Swap space in Linux is used when the amount of physical memory (RAM) is full. If the system needs more memory resources and the RAM is full, inactive pages in memory are moved to the swap space.

While swap space can help machines with a small amount of RAM, it should not be considered a replacement for more RAM. Swap space is located on hard drives, which have a slower access time than physical memory.

Swap space can be a dedicated swap partition (recommended), a swap file, or a combination of swap partitions and swap files.

The size of your swap should be equal to twice your computer's physical RAM for up to 2 GB of physical RAM. For physical RAM above 2 GB, the size of your swap should be equal

Some of useful commands in Swap creation

mkswap:used to format the partition with swap file system

swapon:to turnon the swap

swapoff:to turnoff the swap

Creation of swap partition

To accomplish this task you must be login form root account. So first login from root and verify your hard disk status with fdisk –l command ( This command will show that where your hard disk is mounted. You should use the mount point which show in the output of this command. For example if you see /dev/hda then you should use fdisk /dev/hda in next command. Or if you see /dev/sdb then you should use fdisk /dev/sdb in next command.

[root@raju]#fdisk /dev/sda

command(mfor help):n

command(mfor help):e

First cylinder ("36495-38913", default 36495):

Using default value 36495

Last cylinder, +cylinders or +size{K,M,G} ("3649538913", default 38913): +500M

Command (m for help):t

Command (m for help): 82 #file type of swap space is 82 so change file type to 82 of this newly created partition

Command (m for help): w

[root@raju]#Partx -a /dev/sda

[root@raju]#mkswap –f /dev/sda5

[root@raju]#swapon –a /dev/sda5

[root@raju]#swapon –s

Mounting swap partition

[root@raju~]#vi /etc/fstab

/dev/sda4 swap swap defaults 0 0

[root@raju~]#mount –a

To remove the swap partition

Turnoff swap

[root@raju~]#swapoff /dev/sda5

Remove the entry from rc.local

Remove the partition from /etc/fstab

Reboot the system

Job Automation

noreply@blogger.com (Anonymous) — Sun, 25 Nov 2012 14:24:00 +0000

Job Automation

In Linux, tasks can be configured to run automatically within a specified period of time, on a specified

date, or when the system load average is below a specified number. Red Hat Enterprise Linux is preconfiguredto run important system tasks to keep the system updated. A system administrator can use automatedtasks to perform periodic backups, monitor the system, run custom scripts, and more.

Red Hat Enterprise Linux comes with several automated tasks utilities: crontab, at.

Crontab

Crontab is a daemon that can be used to schedule the execution of recurring tasks according to acombination of the time, day of the month, month, day of the week, and week.

Service profile

Service: crond

Package: crontab

Configuration file: /etc/crontab

/etc/cron.deny

/etc/cron.allow

Objective :To schedule a job

Install the package

[root@raju~]#yum install crontab* -y

Configuring Cron Tasks

To create new task we use crontab -e

[root@raju~]#crontab –eu username

minute hour day month dayofweek command

minute — any integer from 0 to 59

hour — any integer from 0 to 23

day — any integer from 1 to 31 (must be a valid day if a month is specified)

month — any integer from 1 to 12 (or the short name of the month such as jan or feb)

dayofweek — any integer from 0 to 7, where 0 or 7 represents Sunday (or the short name of the week such as sun or mon)

You can see a list of active crontab entries by entering the following terminal command:

crontab -l

You can remove crontab entries by entering the following terminal command:

crontab -r

NOTE:The crontab that you created with the crontab command is stored in /etc/spool/cron under the name of the user who created it. So the above crontab is stored in /etc/spool/cron/ian

In addition to the user crontab files in /var/spool/cron, cron also checks /etc/crontab and files in the /etc/cron.d directory. These system crontab have one additional field between the fifth time entry (day) and the command. This additional field specifies the user for whom the command should be run, normally root

Controlling Access to Cron

T he /etc/cron.allow and /etc/cron.deny files are used to restrict access to cron. The format of both access control files is one username on each line. Whitespace is not permitted in either file.

Examples

[root@raju~]#crontab –eu koti #will create task for user koti

10 20 * 8 * /usr/bin/free

[root@raju~]#chkconfig crond on

[root@raju~]#service crond restart

[root@raju~]#crontab –l koti # will list the job schedules of user koti

[root@raju~]#vi /etc/cron.deny

Shiva #deny cronjobs access to user shiva

At job

While cron is used to schedule recurring tasks, the at command is used to schedule a one-time task at a specific time

Service profile

Service: atd

Package: at

Configuration file: etc/at.deny

/etc/at.allow

Objective:To schedule a job at specified time

Install the package

[root@raju~]#yum install at* -y

T o schedule a one-time job at a specific time, type the command at time, where time is the time to execute the command.

The argument time can be one of the following:

HH:MM format — For example, 04:00 specifies 4:00 a.m. If the time is already past, it is executed at

the specified time the next day.

midnight — Specifies 12:00 a.m.

noon — Specifies 12:00 p.m.

teatime — Specifies 4:00 p.m.

month-name day year format — For example, January 15 2002 specifies the 15th day of January in the year 2002. T he year is optional.

MMDDYY, MM/DD/YY, or MM.DD.YY formats — For example, 011502 for the 15th day of January in the year 2002.

now + time — time is in minutes, hours, days, or weeks. For example, now + 5 days specifies that the command should be executed at the same time five days from now.

After typing the at command with the time argument, the at> prompt is displayed. T ype the commandto execute, press Enter, and type Ctrl+D. Multiple commands can be specified by typing eachcommand followed by the Enter key. After typing all the commands, press Enter to go to a blank lineand type Ctrl+D.

Options

-f Read the commands or shell script from a file instead of specifying them at the prompt.

-m Send email to the user when the job has been completed.

-v Display the time that the job is executed.

-l to list the jobs that are scheduled

Controlling Access to at

The /etc/at.allow and /etc/at.deny files can be used to restrict access to the at commands.

Examples

[root@raju~]#at 10:30 #will schedule following jobs at 10:30

At>date

At>hostname

At>ctl+D

Group Administration

noreply@blogger.com (Anonymous) — Sat, 24 Nov 2012 18:12:00 +0000

Group Administration

Linux uses groups to define a set of related user accounts that can share access to a file or directory.

Important points:

A user can be participant to more than one group at the same time.

A user who is member of a group can change to that group without password but when a user was not member can only change to that group if the group password exist and the user gives it.

One or more users can become group administrators for specific groups.

Group Administrators can:

· add/change/delete the password of the group

· add/delete users to the group

· reserve the group to members only

Types of groups

There are two types of groups. They are

Primary group: These groups are created automatically when user was created.

Secondary group: these groups are created by the admin manually.

The groups configuration files:

/etc/group: Where all the users for each groups are listed.

Format:

groupname: Password or x or ! : GID: Memberlist

/etc/gshadow: Where the groups passwords are kept

Format:

groupname : Password or ! : AdminUsersList : MemberUsersList

Creating a group

To create a new group, use the groupadd command:

groupadd group

where group specifies the name of the group to be added. Groups are stored in the file /etc/group, which can be read by any user but modified only by root.

Options:

-g gid for users

-o to override

Deleting a group

To delete a group, user the groupdel command.

groupdel group

where group specifies the name of the group to be deleted.

Group membership

To add user or delete users to group we use the gpasswd command

gpasswd [options] group

where group specifies the name of the group to be assigned to users

Options:

a user Adds permanently a user to a group

d user Deletes permanently a user from a group.

-A adds a group administrator

-M adds multiple users to the group

Modifying a group

groupmod command is used to modify the group contents

groupmod [options] group

where group specifies the name of the group to be modified

options

-n to assign new name for group

-p to change password

-g to change gid

Examples:

groupadd -g 600 Student

groupmod –g 700 student

groupmod –n teachers student

gpasswd -M raju koti Student

gpasswd –d raju Student

gpasswd –a raju Student

groupdel Student

User Administration

noreply@blogger.com (Anonymous) — Fri, 23 Nov 2012 15:39:00 +0000

User Administration

Every process on the system runs as a particular user.Every file is owned by a particular user.Access to files and directories are restricted by user.the user associated with the running process determines the files and directories accessible to that process

There are three different types of users are present in the linux .they are

Super user

Super user is a user who will have all the permissions over the system. He will have complete authority on the system.

Root user is the super user

System user

The users created during the installation of the operating system are known as super users.supers users are also created when we deploy any application or install any server

Normal user

These users are created manually

UID

A user ID (UID) is a unique positive integer assigned by a Unix-like operating system to each user. Each user is identified to the system by its UID, and user names are generally used only as an interface for humans.

UID for:

Super user :0

Systemusers:1-499

Normal users:500-60,000

User creation

useradd command is used to create the new users

Options

-d to create home directory

-s to create Shell

-p to assign password

-g primary group assigned to the users

-G Other groups the user belongs to

-m Create the user's home directory

-c comment

The users created are specified in a /etc/passwd

Format

user-name:x:user-number:group-number:comment section:/home-directory:default-shell

The fields are:

1.Username: It is used when user logs in. It should be between 1 and 32 characters in length.

2.Password: An x character indicates that encrypted password is stored in /etc/shadow file.

3.User ID (UID): Each user must be assigned a user ID (UID). UID 0 (zero) is reserved for root and UIDs 1-99 are reserved for other predefined accounts. Further UID 100-999 are reserved by system for administrative and system accounts/groups.

4.Group ID (GID): The primary group ID (stored in /etc/group file)

5.User ID Info: The comment field. It allow you to add extra information about the users such as user's full name, phone number etc. This field use by finger command.

6.Home directory: The absolute path to the directory the user will be in when they log in. If this directory does not exists then users directory becomes /

7.Command/shell: The absolute path of a command or shell (/bin/bash). Typically, this is a shell. Please note that it does not have to be a shell.

Login shell(/bin/bash):Those users who will have an interactive access of default shell is called as login shell. Those users who will have login shell can easily login

No login(/sbin/nologin): Those users who doesn’t have interactive access of default shell

Note :Super user and normal user will have login shell and System users will have no login shell

Id command

id username shows user and group id’s

Modify user account

usermod command is used to modify the user accounts

-d to modify home directory

-s to modify Shell

-p to change password

-g change primary group assigned to the users

-G change Other groups the user belongs to

-m change the user's home directory

-c change comment filed comment

Deletion of user

userdel command is used to delete the user

-r option is used to remove the home directory

Assigning a password to user

Passwd command is used to assign password to the user.the /etc/shadow file contains users' encrypted passwords and other information about the passwords.

raju:Ep6mckrOLChF.:10063:0:99999:7:::

1. User name : It is your login name

2. Password: It your encrypted password. The password should be minimum 6-8 characters long including special characters/digits

3. Last password change (lastchanged): Days since Jan 1, 1970 that password was last changed

4. Minimum: The minimum number of days required between password changes i.e. the number of days left before the user is allowed to change his/her password

5. Maximum: The maximum number of days the password is valid (after that user is forced to change his/her password)

6. Warn : The number of days before password is to expire that user is warned that his/her password must be changed

7. Inactive : The number of days after password expires that account is disabled

8. Expire : days since Jan 1, 1970 that account is disabled i.e. an absolute date specifying when the login may no longer be used

Options:

-r Specifies the repository to which an operation is applied. The supported repositories are files, nis or nisplus.

-a Show password attributes for all entries.

-d Deletes password for name. The login name will not be prompted for password. It is only applicable to the files repository.

-l Locks password entry for name.

-e Change the login shell.

-f Force the user to change password at the next login by expiring the password for name.

-g Change the gecos (finger) information. For the files repository, this only works for the superuser. Normal users may change the nis or nisplus repositories.

-h Change the home directory.

-n min Set minimum field for name. The min field contains the minimum number of days between password changes for name. If min is greater than max, the user may not change the password.

-s Displays information including your username and if you do/don't have a password (This command will not actually show the password.)

mm/dd/yy The month date and year that the password was last changed. This information is derived from the Greenwich Mean Time (Universal Time) and therefore may differ by as much as a day in some times zones.

min The minimum number of days between password changes.

max The maximum number of days the password is valid for the name.

warn The number of days relative to max before the passwd uses pam for password management.

-w warn Set warn field for name. The warn field contains the number of days before the password expires and the user is warned. This option is not valid if password aging is disabled.

Last command

last :show listing of last logged in users

Examples :

Useradd –s /bin/sh –c”systemadmin” –d /raju –u 1228 –p “redhat” –G RHCE Raju

Usermod –s /bin/bash –d /raju –u 1220 –p “redhat123” –G Redhat Raju

Userdel –r Raju

passwd –s Raju

Softwares

noreply@blogger.com (Anonymous) — Thu, 22 Nov 2012 19:55:00 +0000

1.PuTTY
PuTTY is a client program for the SSH, Telnet and Rlogin network protocols.

Download putty

2.RealVNC 5.0.1

VNC stands for Virtual Network Computing. It is remote control software which allows you to view and interact with one computer (the “server”) using a simple program (the “viewer”) on another computer anywhere on the Internet.

Download RealVNC 5.0.1

Partition

noreply@blogger.com (Anonymous) — Thu, 22 Nov 2012 17:11:00 +0000

Partition

Partitioning is a means to divide a single hard drive into many logical drives. A partition is contiguous set of blocks on a drive that are treated as an independent disk.

Purpose of partition

Ease of use - Make it easier to recover a corrupted file system or operating system installation.

Performance - Smaller file systems are more efficient. You can tune file system as per application such as log or cache files. Dedicated swap partition can also improve the performance (this may not be true with latest Linux kernel 2.6).

Security - Separation of the operating system files from user files may result into a better and secure system. Restrict the growth of certain file systems is possible using various techniques.

Backup and Recovery - Easier backup and recovery.

Stability and efficiency - You can increase disk space efficiency by formatting disk with various block sizes. It depends upon usage. For example, if the data is lots of small files, it is better to use small block size.

Testing - Boot multiple operating systems such as Linux, Windows and FreeBSD from a single hard disk.

Types of partition

There are three types of partions are there .they are

Primary

A primary partition may contain an operating system along with any number of data files (for example, program files, user files, and so forth). Before an OS is installed, the primary partition must be logically formatted with a file system compatible to the OS. If you have multiple primary partitions on your hard disk, only one primary partition may be visible and active at a time. The active partition is the partition from which an OS is booted at computer startup. Primary partitions other than the active partition are hidden, preventing their data from being accessed. Thus, the data in a primary partition can be accessed (for all practical purposes) only by the OS installed on that partition.
If you plan to install more than one operating system on your hard disk, you probably need to create multiple primary partitions; most operating systems can be booted only from a primary partition.

Extended

An extended partition does not directly hold data. You must create logical partitions within the extended partition in order to store data. Once created, logical partitions must be logically formatted, but each can use a different file system.

Logical Partition

Logical partitions is partition that are created inside the extended partition

Partition Creation

fdisk command is used to create a partition

d:deleate a partition

n:add a new partition

p:print partition table

q:quit without saving changes

w:write table to disk and exit

t:to select the type of partition

partprobe command is used to update the partition table

mkfs.<filesystem name>:used to format filesystem

mount <partition> <directory name> to mount the directory
umount <directory name> to unmount the directory

Note: we have to use /etc/fstab to mount partition permanently

Example:

[root@raju]#vi /etc/fstab

/dev/sda4 /raju ext4 defaults 0 0

[root@raju]#fdisk /dev/sda

command(mfor help):n

First cylinder (36495-38913, default 36495):

Using default value 36495

Last cylinder, +cylinders or +size{K,M,G} (36495-38913, default 38913): +100M

Command (m for help): w

[root@raju]#partx -a /dev/sda

[root@raju]#mkfs.ext4 /dev/sda5

[root@raju]#mkdir /raju

[root@raju]#vi /etc/fstab

/dev/sda4 /raju ext4 defaults 0 0

LVM

noreply@blogger.com (Anonymous) — Thu, 22 Nov 2012 16:56:00 +0000

Logical Volume Manager (LVM)

LVM is a method of allocating hard drive space into logical volumes that can be easily resized instead of partitions.With LVM, the hard drive or set of hard drives is allocated to one or more physical volumes. A physical volume can not span over more than one drive.

The physical volumes are combined into logical volume groups, with the exception of the /boot/ partition. The /boot/ partition can not be on a logical volume group because the boot loader can not read it. If the root / partition is on a logical volume, create a separate /boot/ partition which is not a part of a volume group.

Since a physical volume can not span over more than one drive, to span over more than one drive, create one or more physical volumes per drive.

The logical volume group is divided into logical volumes, which are assigned mount points such as /home and / and file system types such as ext3. When "partitions" reach their full capacity, free space from the logical volume group can be added to the logical volume to increase the size of the partition. When a new hard drive is added to the system, it can be added to the logical volume group, and the logical volumes that are the partitions can be expanded.

Some of useful commands in LVM creation

1. pvcreate is used to create physical volume group

2. vgcreate is used to create volume group

3. lvcreate is used to create logical volume

4. lvresize is used to resize the the logical volume

5. resize2fs is used to update the resized volume

6. vgextend is used to extend the size of volume group

Example to create LVM

[root@raju]#fdisk /dev/sda

command(mfor help):n

command(mfor help):e

First cylinder ("36495-38913", default 36495):

Using default value 36495

Last cylinder, +cylinders or +size{K,M,G} ("3649538913", default 38913): +100M

Command (m for help):t

Command (m for help): 8e

Command (m for help): w

[root@raju]#Partx -a /dev/sda

[root@raju]#pvcreate /dev/sda5

[root@raju]#vgcreate -s 25M Cisco /dev/sda4 #creates volume group named Cisco

[root@raju]#lvcreate - l 4 –n CCNA Cisco #creates 4 extends of volume group 25mb

[root@raju]#mkfs.ext4 /dev/mapper/Cisco

[root@raju]#mkdir /raju

[root@raju]#vi /etc/fstab

/dev/Cisco/CCNA /raju ext4 defaults 0 0

YUM package management

noreply@blogger.com (Anonymous) — Tue, 20 Nov 2012 17:02:00 +0000

YellowdogUpdatedModifier(YUM)

YellowdogUpdatedModifier(YUM)is a software package manager that installs, updates, and removes packages on RPM-based systems. It automatically computes dependencies and figures out what things should occur to install packages. yum makes it easier to maintain groups of machines without having to manually update each one using rpm.

Features include:

Support for multiple repositories
Simple configuration
Dependency calculation
Fast operation
RPM-consistent behavior
Package group support, including multiple-repository groups
Simple interface

yum uses an online repository by default, but you can also configure it to use a local repository of packages.

yum commands are typically run as yum <command> <package name/s>. By default, yum will automatically check all configured repositories to resolve all package dependencies during an installation/upgrade.

YUM Server configuration

Insert the DVD

[root]@raju~]#mount /dev/cdrom /mnt

[root]@raju~]#ls

[root]@raju~]# rpm ivh vsftpd-*.rpm

[root@raju~]#vi /etc/vsftpd/vsftpd.conf

anonymous_enable=yes

:wq!

[root]@raju~]# chkconfig vsftpd on

[root]@raju~]# service vsftpd restart

[root]@raju~]# cp –rvfp /mnt/Server/Packages /var/ftp/pub

[root]@raju~]# cd /var/ftp/pub/Server

[root@Packages]#rpm –ivh createrepo-*.rpm

[root@Packages]#createrepo –V /var/ftp/pub

[root@raju~]cd /etc/yum.repos.d/

[root@yum.repos.d]#vi redhat.repo

[Server]

name=rhel6

baseurl=file:///var/ftp/pub/Server

enabled=1

gpgcheck=0

:wq!

[root@raju~]#yum clean all

[root@raju~]#yum list all

Client configuration

[root@client]cd /etc/yum.repos.d/

[root@yum.repos.d]#vi redhat.repo

[redhat]

name=rhel6

baseurl=ftp://192.168.0.254/pub/Server

enabled=1

gpgcheck=0

:wq!

[root@raju~]#yum clean all

[root@raju~]#yum list all

The following is a list of the most commonly-used yum commands. For a complete list of available yumcommands, refer to man yum.

yum install <package name/s>

Used to install the package or group of packages.

yum update <package name/s>

Used to update the specified packages to the latest available version.

yum check-update

This command allows you to determine whether any updates are available for your installed packages. yum returns a list of all package updates from all repositories if any are available.

yum remove <package name/s>

Used to remove specified packages, along with any other packages dependent on the packages.

yum reinstall <package name/s>

Used to reinstall specified packages, along with any other packages dependent on the packages.

yum provides <file name>

Used to determine which packages provide a specific file or feature.

yum search <keyword>

This command is used to find any packages containing the specified keyword in the description, summary, packager and package name fields of RPMs in all repositories.

yum localinstall <absolute path to package name/s>

Used when using yum to install a package located locally in the machine.

Redhat Package Manager

noreply@blogger.com (Anonymous) — Tue, 20 Nov 2012 14:13:00 +0000

Redhat Package Manager(RPM)

RPM is a used for both installation and package format.

RPM packages were mainly created for redhat linux but now many linux distributions are using this

RPM is used to

->Install new package

->upgrage existing packages

->Remove installed applications

Query packages

RPM Label Pattern

Package Name-Package version.package architechture.package extension

Ex:Bind-9.3.3-7.el5.i386.rpm

Bind-package name ,9.3.3-7.el5-package version,i386-package architechture,rpm-package extension

Syntax of package

[root@raju~]#rpm <option> <package name> --force

Options:-

-i: to install package

-v: verbose

-h:Displays the progess in hashes

-U:to update existing package

--force:install package forcefully

-e:to remove package

--nodeps :to remove dependencies package

-q:query the availability of package

-qa:list all the installed packages

-qc:Displays the configuration files of the package

-qi-displays information of package

-ql:Displays all the files associated with the installed package

-qs:to check the status of package

For sharing the packages over a network we have to mount the packages

[root@raju~]#mkdir /mnt/packages

[root@raju~]#mount 192.168.0.254:/var/ftp/pub/Server /mnt/packages

[root@raju~]#mount

[root@raju~]#cd/mnt/packages

[root@raju~]#ls

Displays all rpm packages under /mnt /packages

Examples:

Install and Upgrade the packages

[root@raju~]#rpm –ivh samba-* .rpm #to install the package with verbose and hash progress

[root@raju~]#rpm –i vsftpd-*.rpm #to install the package

[root@raju~]#rpm –iv nfs*.rpm #to install the package verbosefully

[root@raju~]#rpm –ivh pptpd*.rpm --force #to install the package with verbose, hash progress and forcefully

[root@raju~]#rpm –Uvh samba-*.rpm #to upgrade the package with verbose and hash progress

Removal of installed packages

[root@raju~]#rpm –e samba-* .rpm #to remove the package

[root@raju~]#rpm –e samba-*.rpm --nodeps #to remove package dependencies

Quering the packages

[root@raju~]#rpm -qa #to query all installed packages

[root@raju~]#rpm –q samba-*.rpm #to query particular packages

[root@raju~]#rpm –qd samba-*.rpm #to view the documentation of packages

[root@raju~]#rpm –ql samba-* .rpm #to list of files of particular packages

[root@raju~]#rpm –qc samba-*.rpm #to configure the files of package

root@raju~]#rpm –qi samba-*.rpm #to view the information of the packages

[root@raju~]#rpm –qs samba-*.rpm #to view the status of the packages

VPN server

noreply@blogger.com (Anonymous) — Mon, 19 Nov 2012 13:16:00 +0000

Virtual private network (VPN)

A virtual private network (VPN) extends a private network and the resources contained in the network across public networks like the internet. It enables a host computer to send and receive data across shared or public networks by emulating the properties of the private network such as shares, server access, and printers by establishing and maintaining the security and management policies of the private network.

VPN server configuration using PPTP

Service profile

Service: pptpd

Package: pptpd

Port no:1723(TCP)

Configuration file: /etc/pptpd.conf

/etc/ppp/chap-secrets

Script file: /etc/ init.d/pptpd

Daemons: pptpd

Objective :To act extends a private network and the resources contained in the network across public networks

Install the package

[root@vpn~]#yum install pptpd* -y

Edit the main configuration file

[root@vpn~]#vi /etc/pptpd.conf

localip 192.168.0.1
remoteip 192.168.0.2-254

:wq!

Now set the VPN login ID and password

[root@vpn~]#vi /etc/ppp/chap-secrets

Vpnusername pptpd vpnpassword * # * indicates the vpn client ip and pptpd is fixed

Note: instead of * we can use different client address

:wq!

[root@vpn~]#chkconfig pptpd on

[root@vpn~]#service pprtpd restart

Client configuration for windows Xp

Start->control panel->network connections->Setup a new connection or network->in the network connection wizard,click next->select connect to the network at my work place and then click next->select VPN connection and click next->selct don’t dial initial connection and click next->vpn server IP ->ask to selct smart card->Finish

Then goto networkconnection and right click on the new connection and selct connect

OpenVPN configuration

Service profile

Service: openvpn

Package: openvpn

Port no:1194(UDP)

Configuration file: /etc/openvpn/myhomelan

/etc/openvpn/myhomelan/local.conf

Script file: /etc/ init.d/openvpn

Daemons: openvpn

Objective :To act extends a private network and the resources contained in the network across public networks

Install the package

[root@vpn~]# yum install openvpn* -y

Create a directory

[root@vpn~]#mkdir /etc/openvpn/myhomelan

Edit configuration file

[root@vpn~]#cd /etc/openvpn/myhomelan

[root@myhomelan]#openvpn --genkey --secret myhomelan-key.txt

[root@vpn~]#vi /etc/openvpn/myhomelan/local.conf

dev tun if config 192.168.0.1 192.168.0.20

secret /etc/openvpn/myhomelan/homeland-key.txt

comp-lzo

port-1194

user-nobody

group-nobody

:wq!

[root@vpn~]#chkconfig openvpn on

[root@vpn~]#service openvpn restart

Mail server

noreply@blogger.com (Anonymous) — Sun, 18 Nov 2012 16:58:00 +0000

Mail server

Mail server is used to send the email to local or remote systems.

Structure of mail server

Mail Transfer Agent

The Mail Transfer Agent (MTA) is the part of the email system that does much of the work of transferring the email messages from one computer to local or remote systems with /usr/bin/sendmail program. Once configured correctly, most users will not have any direct interaction with their chosen MTA unless they wish to re-configure it for any reason.

Mail User Agent

This is the part of the system that the typical user is likely to be most familiar with. The Mail User Agent (MUA), or mail client, is the application that is used to write, send and read email messages. Anyone who has written and sent a message on any computer has used a Mail User Agent of one type or another.

Mail Delivery Agent

The MDS delivers mail to the recipients .

The Mail Delivery Agent (MDA) sits in the background and performs filtering on the email messages between the Mail Transfer Agent and the mail client (MUA). The most popular form of MDA is a spam filter to remove all the unwanted email messages from the system before they reach the inbox of the user’s mail client (MUA).

SMTP

SMTP is an acronym for Simple Mail Transport Protocol. This is the protocol used by the email systems to transfer mail messages from one server to another. This protocol is essentially the communications language that the MTAs use to talk to each other and transfer messages back and forth.

Relaying: Forwarding a submitted mail to another mail server for delivery when the distance is long.

If the machine needs to pass mail to another mail server to get out to the Internet, the hostname of the mail server should be defined as the Relay Host.

Postfix mail server Configuration

Service profile

Service: postfix

Package: postfix

Port no:25(TCP)

Configuration file: /etc/postfix/main.cf

Script file: /etc/ init.d/postfix

Daemons: postfix

Objective :To act as mail transfer agent

Install the postfix package

[root@mailserver~]#yum install postfix* -y

Edit main Configuration file

[root@mailserver~]#vi /etc/postfix/main.cf

myhostname=mailserver.raju.com

mydomain=raju.com

myorigin=desktop1

mynetworks=192.168.0.0/24

#SMTP authentication for our users with postfix

smtpd_sasl_auth_enable = yes

smtpd_sasl_local_domain = raju.com

smtpd_recipient_restrictions = permit_mynetworks,permit_sasl_authenticated,reject_unauth_destination

smtpd_sasl_security_options = noanonymous

:wq!

[root@mailserver~]chkconfig postfix on

[root@mailserver~]#service postfix restart

Dovecot

Dovecot is one of the popular POP3/IMAP server which needs MTA like Postfix to work properly.

[root@mailserver~]#yum install devcot* -y

[root@mailserver~]#vi /etc/devcot

Protocols=imap pop3

disable_plaintext_auth=no

#SMTP authentication for users with dovecot.

#Look for the line that starts with auth default, before that insert the lines below.

auth default {

mechanisms = plain login

passdb pam {

}

userdb passwd {

}

socket listen {

client {

path = /var/spool/postfix/private/auth

mode = 0660

user = postfix

group = postfix

}

#rename previous auth default to auth default2. If you dont rename this then dovecot server will give you error like multiple instances of auth default

:wq!

[root@mailserver~]chkconfig postfix on

[root@mailserver~]#service mailserver restart

[root@mailserver~]#chkconfig devcot on

[root@mailserver~]#service devcot restart

Create user for testing

[root@mailserver~]#useradd koti

[root@mailserver~]#useradd raju

logon to raju

[root@raju]mail –s hello koti@mailserver.raju.com

Proxy server

noreply@blogger.com (Anonymous) — Fri, 16 Nov 2012 15:38:00 +0000

Proxy server

Proxy server is used to share the internet connection with many clients

Proxy server can be configured as :

A simple proxy server which used to share the internet connection

A caching web server which is used to store web pages locally to improve performance

A firewall which is used to control to access the internet

Squid proxy is the widely used open source product.

Server Configuration

Service profile

Service: squid

Package:squid

Port no:3128 (default)

Configuration file: //etc/squid/squid.conf

Script file: /etc/ init.d/squid

Daemons: squid

Objective :To share internet connection

[root@proxy~]#yum install squid* -y

Edit the main configuration

[root@proxy~]#vi /etc/squid/squid.conf

##to configure simple proxy##

http_port 3128 #line no.73 3128 is default port we can use any port number other than that

visible_hostname Rajashekar #line no 2831

##to configure caching proxy##

cache_dir ufs/var/spool/squid 100 16 256

##to configure firewall proxy##

##Find the line beginning with acl localhost and At the end of the section, add:

#create rule for particular network

acl rajunetwork src 192.168.0.0/24

##Authorizing access to group

#Locate the line http_access allow and add below (before the line http_access deny all)

http_access allow rajunetwork

##Allow the use non-standard ports

By default, Squid allows HTTP traffic only on specific ports (e.g. 80). This can cause problems on websites using other ports.

##To avoid this deadlock, find the line http_access deny! Safe_ports and the edit it to:

# http_access deny! Safe_ports

:wq!

[root@proxy~]#chkconfig squid on

[root@proxy~]#service squid restart

Client configuration

For proxy browser is a client whether it may be on server or client

For Firefox

Open firefox

Tools->options->advanced tab->network->connection->settings->Manual proxy configuration->

Http proxy server ip port 3128

Apache web server

noreply@blogger.com (Anonymous) — Fri, 16 Nov 2012 14:14:00 +0000

Apache web server

The standard web server on Linux is Apache. The web server is the technology that receives requests from web browsers and servers up the requested web pages to those browsers.
Service profile

Service: httpd

Package: httpd

Port no:80 (http)

Configuration file: /etc/httpd/conf/httpd.conf

/etc/httpd/conf.d/SSL.conf

Script file: /etc/init.d/httpd

Daemons: httpd

Objective :for hosting the websites

Install the package

[root@webserver~]#yum install httpd* -y

Edit main configuration file

[root@webserver~]#vi /etc/hhtpd/conf/httpd.conf

#add the following lines at last

ServerAdmin root@raju.com

ServerName www.raju.com:80

DocumentRoot”/var/www/html”

ErrorLog logs/dummy-www.raju.com-error_log

CustomLog logs/dummy-www.raju.com-access_log common

</VirtualHost>

:wq!

Now resovle the name locally

[root@webserver~]#vi /etc/hosts

192.168.0.254 www.raju.com

:wq!

Create html page

[root@webserver~]#vi /var/www/html/index.html

#****write html code in this and save *****#

:wq!

[root@webserver~]#chkconfig httpd on

[root@webserver~]#service httpd restart

[root@webserver~]#links www.raju.com

Virtual Web Hosting

Configuring multiple sites on single web server is called virtual hosting

There are three different types of virual hosting are there .They are

Name Based: Hosting multiple sites on single ip is called as nambebased virtual hosting

IP Based: Hosting different websites by using different IP addreses i.e, we need individual ip address for each site

Port Based: Hosting the sites using port numbers other than the default port number.

Name Based Virtual hosting

Edit main configuration file

[root@webserver~]#vi /etc/hhtpd/conf/httpd.conf

Document Root “var/www/virtual” #search for DocumentRoot and add this line below to it

NameVirtualHost 192.168.0.254 #search for NameVirtualHost and make it as seen here

#add the following lines at last

ServerAdmin root@raju.com

ServerName www.raju.com

DocumentRoot”/var/www/virtual”

DirectoryIndex raju.html

ErrorLog logs/dummy-www.raju.com-error_log

CustomLog logs/dummy-www.raju.com-access_log common

</VirtualHost>

ServerAdmin root@koti.com

ServerName www.koti.com

DocumentRoot”/var/www/virtual”

ErrorLog logs/dummy-www.koti.com-error_log

CustomLog logs/dummy-www.koti.com-access_log common

</VirtualHost>

:wq!

Now resovle the name locally

[root@webserver~]#vi /etc/hosts

192.168.0.254 www.raju.com

192.168.0.254 www.koti.com

:wq!

Create html pages

[root@webserver~]#mkdir /var/www/virtual

[root@webserver~]#vi /var/www/virtual/raju.html

#****write html code in this and save *****#

:wq!

[root@webserver~]#vi /var/www/virtual/koti.html

#****write html code in this and save *****#

:wq!

[root@webserver~]#chkconfig httpd on

[root@webserver~]#service httpd restart

[root@webserver~]#links www.raju.com

[root@webserver~]#links www.koti.com

IP Based Virtual Hosting

[root@webserver~]#vi /etc/hhtpd/conf/httpd.conf

Document Root “var/www/virtual” #search for DocumentRoot and add this line below to it

#add the following lines at last

ServerAdmin root@raju.com

ServerName www.raju.com

DocumentRoot”/var/www/virtual”

DirectoryIndex raju.html

ErrorLog logs/dummy-www.raju.com-error_log

CustomLog logs/dummy-www.raju.com-access_log common

</VirtualHost>

ServerAdmin root@koti.com

ServerName www.koti.com

DocumentRoot”/var/www/virtual”

ErrorLog logs/dummy-www.koti.com-error_log

CustomLog logs/dummy-www.koti.com-access_log common

</VirtualHost>

:wq!

Now resovle the name locally

[root@webserver~]#vi /etc/hosts

192.168.0.254 www.raju.com

192.168.0.253 www.koti.com

:wq!

[root@webserver~]#mkdir /var/www/virtual

[root@webserver~]#vi /var/www/virtual/raju.html

#****write html code in this and save *****#

:wq!

[root@webserver~]#vi /var/www/virtual/koti.html

#****write html code in this and save *****#

:wq!

[root@webserver~]#chkconfig httpd on

[root@webserver~]#service httpd restart

[root@webserver~]#links www.raju.com

[root@webserver~]#links www.koti.com

Port Based Virtual Hosting

[root@webserver~]#vi /etc/hhtpd/conf/httpd.conf

Document Root “var/www/virtual” #search for DocumentRoot and add this line below to it

#change the following lines

ServerAdmin root@raju.com

ServerName www.raju.com

DocumentRoot”/var/www/virtual”

DirectoryIndex raju.html

ErrorLog logs/dummy-www.raju.com-error_log

CustomLog logs/dummy-www.raju.com-access_log common

</VirtualHost>

ServerAdmin root@koti.com

ServerName www.koti.com

DocumentRoot”/var/www/virtual”

ErrorLog logs/dummy-www.koti.com-error_log

CustomLog logs/dummy-www.koti.com-access_log common

</VirtualHost>

:wq!

Now resovle the name locally

[root@webserver~]#vi /etc/hosts

192.168.0.254 www.raju.com

192.168.0.254 www.koti.com

:wq!

[root@webserver~]#mkdir /var/www/virtual

Create html page

[root@webserver~]#vi /var/www/virtual/raju.html

#****write html code in this and save *****#

:wq!

[root@webserver~]#vi /var/www/virtual/koti.html

#****write html code in this and save *****#

:wq!

[root@webserver~]#chkconfig httpd on

[root@webserver~]#service httpd restart

[root@webserver~]#links www.raju.com

[root@webserver~]#links www.koti.com

Client Side configuration

[root@webserver~]#vi /etc/hosts

192.168.0.254 www.raju.com

192.168.0.253 www.koti.com

Open browser and enter the website name

Routing

noreply@blogger.com (Anonymous) — Thu, 15 Nov 2012 13:36:00 +0000

Routing

The process of forwarding packets from one network to another network choosing the best path by using the administrative distance from the routing table
Routing table consists of the best routes for every destination.
Administrative Distance (AD) is a value that routers use in order to select the best path when there are two or more different routes to the same destination from two different routing protocols. Administrative Distance counts the reliability of a routing protocol. Administrative Distance (AD) is a numeric value which can range from 0 to 255. A smaller Administrative Distance (AD) is more trusted by a router, therefore the best Administrative Distance (AD) being 0 and the worst, 255.

Route Source	Default Distance Values
Connected interface	0
Static route	1
Enhanced Interior Gateway Routing Protocol (EIGRP) summary route	5
External Border Gateway Protocol (BGP)	20
Internal EIGRP	90
IGRP	100
OSPF	110
Intermediate System-to-Intermediate System (IS-IS)	115
Routing Information Protocol (RIP)	120
Exterior Gateway Protocol (EGP)	140
On Demand Routing (ODR)	160
External EIGRP	170
Internal BGP	200
Unknown*	255

Types of routing

There are three types of routing.They are

Static routing
Default routing
Dynamic routing

Static routing

It is configured by the administrator manually

It is secure and fast

It was mainly used by the small organization which consists of less no. of routers

Administrative distance for static route is 0 and 1.

Disadvantages

Used for small network

Everything should be done manually

Network change effect the complete network

Configuration of Static route

Router#config terminal

Router(config)#ip routing

Router(config)#ip route <Destination Network> <Destination Subnet Mask> <next-hop address>

outer(config)#ip route <Destination Network> <Destination Subnet Mask> <Exit interface> <administrative distance> <permanent>

Note:-Administrative distance and permanent are the optional entries

Examples

Ex-1:

Router#Config terminal

Router (config)#ip routing

Router (config)#ip route 192.168.0.1 255.255.255.0 192.168.0.3

Ex-2:

Router#Config terminal

Router(config)#ip routing

Router(config)#ip route 192.168.0.1 255.255.255.0 s0 1 P

Default Routing

Manually adding the single route for the entire destination is known as default route.
Default route used when destination is unknown.
This was the last preferred route in the routing table.
When there was no entry for the destination network in a routing table, the router will forward the packets o its default route.
It will help in reducing the size of our routing table.

Configuration of Default route

Router#config terminal

Router(config)#ip routing

Router(config)#ip route 0.0.0.0 0.0.0.0 <next-hop address>

outer(config)#ip route 0.0.0.0 0.0.0.0 <Exit interface> <administrative distance> <permanent>

Note:-Administrative distance and permanent are the optional entries

Examples

Ex-1:

Router#Config terminal

Router (config)#ip routing

Router (config)#ip route 0.0.0.0 0.0.0.0 192.168.0.3

Ex-2:

Router#Config terminal

Router(config)#ip routing

Router(config)#ip route 0.0.0.0 0.0.0.0 S0 1 P

Dynamic routing

Dynamic routing use Routing Protocols that dynamically discover network destinations and how to get to them. Dynamic routing allows routing tables in routers to change if a router on the route goes down. Examples of Routing Protocols are RIP, EIGRP and OSPF.

There are three basic types of routing protocols.They are

Distance-vector

Link-state

Hybrid

Distance-vector Routing Protocols: Distance-vector Routing Protocols use simple algorithms that calculate a cumulative distance value between routers based on hop count.

Example: RIP1, RIP2, IGRP

Hop count: A routing metric that calculate the distance between a source and destination on the number of routers in the path.

Link-state Routing Protocols: Link-state Routing Protocols use sophisticated algorithms that maintain a complex database of internetwork topology.

Example: OSPF IS-IS

Hybrid Routing Protocols: Hybrid Routing Protocols use a combination of distance-vector and link-state methods that tries to incorporate the advantages of both and minimize their disadvantages.

Example: EIGRP

NIS(Network Information Service)

noreply@blogger.com (Anonymous) — Wed, 14 Nov 2012 16:56:00 +0000

NIS(Network Information Service)

NIS is also called as YP. YP stands for Yellow Pages.

An NIS maintains a central directory of user and group information,hostname etc ina computer network

Server Configuration

Service Profile

Packages:ypserv,ypbind,yptools

Configuration file;/var/yp/Makefile

Daemon:ypserv,yppassdd

Portnumbers:NIS uses random port numbers

Install the packages

[root@nisserver~]#yum install ypserve* -y

[root@nisserver~]#yum install ypbind* -y

[root@nisserver~]#yum install yptool* -y

Set the NISDOMAIN in the /etc/sysconfig/network file as shown below.

[root@nisserver~]# vi /etc/sysconfig/network

NETWORKING=yes

HOSTNAME=Raju

GATEWAY=192.168.0.254

NISDOMAIN=raju.com

[root@nisserver~]# vi /etc/sysconfig/authconfig

USENIS=YES

Create the database

To create the database execute the following command and type yes

[root@nisserver~]#/usr/lib/yp/ypinit –m

[root@nisserver~]#ls –l /var/yp #will list the created databases

Edit the configuration file

[root@nisserver yp~]#make #to update database

Edit main configuration file

[root@nisserver~]# vi /var/yp/Makefile

NOPUSH=false

MERGE_PASSWD=false

Start the services

[root@nisserver~]#Service ypserve restart

[root@nisserver~]#Service yppasswdd restart

[root@nisserver~]#Service portmap restart

[root@nisserver~]#Service nfs restart

[root@nisserver~]#Service ypbind restart

[root@nisserver~]#Service ypxfrd restart

Note:Configure nfs with NIS to provide users home directory in client machine they logged in

Client Configuration

[root@nisclient~]# vi /etc/sysconfig/network

NETWORKING=yes

HOSTNAME=Koti

GATEWAY=192.168.0.1

NISDOMAIN=raju.com

Install ypbind package

[root@nisclient~]#yum installypbind* -y

[root@nisclient~]#service ypbind restart

[root@nisclient~]#system-config-authentication

Select Use NIS

[OK]

Select

Domanin=>raju.com

Server=>192.168.0.254

To configure a Windows client

Download the pGina plug-in for windows and install it.

· Select Start ->Programs->pGina->Configuration Tool to run the pGina configuration tool.

· Then click on "Plugin" tab and click "Browse." Enter the path to the .dll that you just installed that performs the NIS function. The default location is c:\pGina\plugins\NISplugin.dll

· Then on the "Plugin" tab, click the "Configure" button. In the dialog box named, appropriately, "Dialog," enter the name of your NIS domain (raju.com in the example).

· You'll also see a text box in which to enter the "Password Map" file. Enter passwd.byname. This is the table in NIS that is used when you pass in a username at logon time.

· At the "Dialog" dialog box, click "Save." At the "pGina Configuration" window, click "OK."

· Reboot the client machine to save the settings.

· After reboot we will find pGina login as shown below

Samba Server

noreply@blogger.com (Anonymous) — Wed, 14 Nov 2012 14:29:00 +0000

Samba Server

Samba is the standard Windows interoperability suite of programs for Linux and UNIX.

Samba sets up network shares of Linux and UNIX directories .These directories will appear to windows users as normal folders accessible via network

UNIX users can mount the shares directly as part of their file structure

Service profile

Package: samba

Service:smb

Deamons:nmbd ,smbd

Configuration file:/etc/samba/smb.conf

Script file:/etc/init.d/samba

Port no: 137 NetBios Name service

138 NetBios Datagram Service

139 NetBios Session Service

Objective:To share the files among the cross platform

Install the Packages

[root@smb~]#Yum install samba* -y

Create the resources on Samba server i.e, files/folders and users

[root@smb~]#useradd raju

[root@smb~]#useradd koti

[root@smb~]#passwd ****

Create shared folder /var/raju with full permission and some files inside

[root@smb~]#mkdir /var/raj

[root@smb~]#chmod 777 /var/raj

[root@smb~]#cd /var/raj

[root@smb~]#touch file[1..10] #creates files i.e, file1 to file10

Edit the main configuration

[root@smb~]#vi /etc/samba/smb.conf

#go to end of the file copy last 8 lines 8yy and press p to paste

[redhat] #shared name

comment=this is for redhat

path=/var/raj

valid users= raju koti

public=no

writable=yes

printable=yes

host allow=192.168.0.0/24

:wq!

Check the syntax of the configuration file

[root@smb~]#testparam

Provide a separate samba password for the samba users to getsamba shares

[root@smb~]#smbpasswd –a raju

[root@smb~]#smbpasswd –a koti

[root@smb~]#chkconfig smb on

[root@smb~]#service smb restart

Client configuration

In linux

[root@smbclient~]#smbclient //192.168.0.1/redhat –U raj

Password:

Smb:\>ls

Smb:\>get <name of the file to download>

Smb:\>put <name of the file to upload>

Smb:\>exit

In windows

Start-> Run->\\ip\shared name

Provide samba username and password

Kickstart and PXE Server

noreply@blogger.com (Anonymous) — Tue, 13 Nov 2012 07:39:00 +0000

Configuration of Kickstart and PXE Server in RHEL6

Server IP settings

IPADDR 192.168.0.70

SUBNET 255.255.255.0

NM_CONTROLLED=no

ONBOOT= yes

BOOTPRO=none

DNS1=192.168.0.1

Kickstart file is used to install the OS at different client machine without providing the entries which are asked during the installation of OS.Kickstart file should be created in the location os is copied and can be accessed over the network.

Install the kickstart package.

Yum install system-config-kickstart

Install the kickstart package.

Run the kickstart utility.

system-config-kickstart

In the second last option you can remove text mode installation option and opt For a graphical one.

Select the http installation method

Use the defaults.

In the disk label option choose the first option (Initialize the disk label).

The partitions that I have created are like this.

Mount Point type size

/boot ext4 500

Swap swap 2048

/ ext4 18000

Make sure that SELinux option is disabled and Security level is set to Disable firewall.

Save the ks.cfg file to the filesystem.

PXE Server Configuration

# Install all the required packages through yum

[root@server~]#Yum install syslinux xinetd* tftp-server dhcp httpd -y

[root@server~]#mkdir /var/lib/tftpboot/pxelinux.cfg

[root@server~]#cp /usr/share/syslinux/pxelinux.0 /var/lib/tftpboot/

[root@server~]#vi /etc/xinetd.d/tftp

# Open the xinetd settings to enable tftp server.

# at line 14 set the parameter to no from yes.

Disable=no

[root@server~]#service xinetd restart

[root@server~]#chkconfig xinetd on

Add the following code to dhcp server in global section

[root@server~]# vi /etc/dhcp/dhcpd.conf

# Global Options

Allow booting;

Allow bootp;

authoritative;

# Subnet definition

subnet 192.168.0.0 netmask 255.255.255.0 {

# Parameters for the local subnet

option routers 192.168.0.1;

option subnet-mask 255.255.255.0;

option domain-name “Raju.com”;

option domain-name-servers 192.168.0.1;

default-lease-time 21600;

max-lease-time 43200;

# Client IP range

range dynamic-bootp 192.168.0.100 192.168.0.200;

}

[root@server~]#service dhcpd restart

[root@server~]#Chkconfig dhcpd on

[root@server~]#mkdir –p /var/pxe/rhel6

[root@server~]#mkdir /var/lib/tftpboot/rhel6

Insert your RHEL 6 dvd and Mount dvd to /mnt

[root@server~]#mount /dev/cdrom /mnt

Check the contents to see if it is properly mounted /mnt

ls –l

copy all the contents to the /var/pxe/rhel6 directory.

[root@server~]#cp –ivr /mnt/* /var/pxe/rhel6

After the file copy operation unmount and eject the dvd.

[root@server~]#umount /mnt

[root@server~]#eject

copy the vmlinuz and initrd.img files to the tftpboot directory.

[root@server~]#cp /var/pxe/rhel6/images/pxeboot/vmlinuz /var/lib/tftpboot/rhel6

[root@server~]#cp /var/pxe/rhel6/images/pxeboot/initrd.img /var/lib/tftpboot/rhel6

copy the menu file.

[root@server~]#cp /usr/share/syslinux/menu.c32 /var/lib/tftpboot/

[root@server~]#vi /var/lib/tftpboot/pxelinux.cfg/default

timeout 20

default menu.c32

#Prepare the boot menu.

menu title ******BOOT MENU******

label 1

menu label ^ 1) RHEL6

kernel rhel6/vmlinuz

append initrd=rhel6/initrd.img ks=http://192.168.0.70/ks/ks.cfg ksdevice=eth0

[root@server~]#chkconfig httpd on

[root@server~]#service httpd restart

create new entry

[root@server~]# vi /etc/httpd/conf.d/pxeboot.conf

Alias /rhel6 /var/pxe/rhel6

Options Indexes FollowSymLinks

Order Deny,Allow

Deny from all

Allow from 127.0.0.1 192.168.0.0/24

# Ip address you allow

[root@server~]#chkconfig httpd on

[root@server~]#service httpd restart

[root@server~]#mkdir /var/www/html/ks

[root@server~]#cp /ks.cfg /var/www/html/ks/ks.cfg

[root@server~]#chmod 644 /var/www/html/ks/ks.cfg

[root@server~]#chkconfig httpd on

[root@server~]#service httpd restart

The pxe server is ready.

Plug a computer into the network and boot it through LAN using pxe.