Linux Made Easy

How to setup NFS Configuration files (/etc/exports)?

2009-01-12T20:08:00.000-08:00

An entry in /etc/exports will typically look like this:

directory host1(option1,option2) host2(option3,option4)

Where,

directory - the directory or file system you want to share

host1, host2 - Allowed hosts to mount your shared folder. Using IP Address is better idea rather than host name. If the hosts are in your local network, mention their private IP address.

optionXX

ro: The directory is shared read only; the client machine will not be able to write it. This is the default.

rw: The client machine will have read and write access to the directory.

no_root_squash: By default, any file request made by user root on the client machine is treated as if it is made by user nobody on the server. (Exactly which UID the request is mapped to depends on the UID of user "nobody" on the server, not the client.) If no_root_squash is selected, then root on the client machine will have the same level of access to the files on the system as root on the server. This can have serious security implications, although it may be necessary if you want to perform any administrative work on the client machine that involves the exported directories. You should not specify this option without a good reason.

no_subtree_check: If only part of a volume is exported, a routine called subtree checking verifies that a file that is requested from the client is in the appropriate part of the volume. If the entire volume is exported, disabling this check will speed up transfers.

sync: By default, all but the most recent version (version 1.11) of the exportfs command will use async behavior, telling a client machine that a file write is complete - that is, has been written to stable storage - when NFS has finished handing the write over to the filesystem. This behavior may cause data corruption if the server reboots, and the sync option prevents this.

Related Topic - How to setup Network File System (NFS)?

How to setup Network File System (NFS)?

2009-01-12T10:59:00.000-08:00

NOTE: This document does not provide in depth about the configuration file. Also, Please note that installing required modules/packages is not the scope of this document. I will try to provide different article about configuration of /etc/exports (now available here), /etc/sysconfig/nfs and available mount options.

What is NFS?

Network File System (NFS) allows mounting the file system of Remote machine as if it is local file system.

How to Setup an NFS Server?

1. On both NFS Server and Client, make sure your kernel has nfs support. To check

$ cat /proc/filesystems
minix
ext2
msdos
nodev proc
nodev nfs

If you donot see nfs, you have to compile your own kernel with NFS enabled, or have to load the kernel module if your NFS support was compiled as a module.

2. Portmapper – To offer NFS service, portmapper (or rpc.portmap) should be running before starting NFS daemons. To start manually, run rcportmap start.

To check whether portmapper is running or not, run rpcinfo –p. If it is running, you can see portmapper daemon, its version, protocol and port numbers as follows:

$ rpcinfo -p
program vers proto port
100000 2 tcp 111 portmapper
100000 2 udp 111 portmapper
100003 2 udp 2049 nfs
100003 3 udp 2049 nfs
100003 4 udp 2049 nfs
100003 2 tcp 2049 nfs
100003 3 tcp 2049 nfs
100003 4 tcp 2049 nfs
100024 1 udp 32770 status
100021 1 udp 32770 nlockmgr
100021 3 udp 32770 nlockmgr
100021 4 udp 32770 nlockmgr
100024 1 tcp 32769 status
100021 1 tcp 32769 nlockmgr
100021 3 tcp 32769 nlockmgr
100021 4 tcp 32769 nlockmgr
100005 1 udp 644 mountd
100005 1 tcp 645 mountd
100005 2 udp 644 mountd
100005 2 tcp 645 mountd
100005 3 udp 644 mountd
100005 3 tcp 645 mountd

3. Make necessary configuration such as directory to be shared, hosts allowed to use the shared directories and other options in /etc/exports. Addition to that, you may configure such as number of nfs threads required at /etc/sysconfig/nfs

4. Start nfsserver from /etc/init.d, which start all required daemons (rpc.nfsd, rpc.lockd, rpc.statd, rpc.mountd, rpc.rquotad). You may also start these daemons one by one manually.

How to Setup an NFS Client?

To begin using machine as an NFS client, you will need the portmapper running on that machine, and to use NFS file locking, you will also need rpc.statd and rpc.lockd running on both the client and the server

To mount from command line, run as follow (master.foo.com is nfs server, home is the shared folder on that server. /mnt/home is the local mount point):

# mount master.foo.com:/home /mnt/home

To automate this while booting, add an entry as below in /etc/fstab file:
# device mountpoint fs-type options dump fsckorder
...
master.foo.com:/home /mnt nfs rw 0 0
...

Related topic - How to setup NFS Configuration files (/etc/exports)?

How to create/increase swap on the fly in Linux?

2008-12-20T06:33:00.001-08:00

We can either create swap file or swap partition and make it as swap space.

How to create swap space from file?

To create 512MB swap file, run below commands. Make sure the file system has enough diskspace, where you are creating swap file.

dd if=/dev/zero of=swapfile bs=1024 count=524288
chmod 600 swapfile
mkswap swapfile
swapon swapfile

To automate this while rebooting, add following entry to /etc/fstab. (Assumed that you created swapfile under /opt)

/opt/swapfile swap swap defaults 0 0

How to create swap space from partition?

Create a partition using "fdisk" with type swap i.e. make partition type to 82. Type "t" to set the partition type. (Assumed that you created a partition /dev/hdb1 as swap). To activate, run following commands

mkswap /dev/hdb1
swapon /dev/hdb1

To automate this while rebooting, add following entry to /etc/fstab.

/dev/hdb1 swap swap defaults 0 0

Use "free" command before and after executing above methods to verify that the swap has been created / increased

Have Fun .....

Sikkandar.Linux at Gmail.Com

How to Setup or Check Network Speed and Duplex on Linux?

2008-12-06T02:31:00.000-08:00

What is Half and Full Duplex?

In Full duplex, the data (signal) can flow in both directions

In Half duplex, the data (signal) can flow in one direction at a time

So, the duplex settings is very important. To check duplex and speed settings, ethtool is the best tool.

To see the duplex and speed setting of interface eth0 just run following command

# ethtool eth0

To setup, 100 Mbps speed, Full duplex and make it static on interface eth0 , run below command:

# ethtool -s eth0 autoneg off duplex full speed 100

autoneg off make sure that this setting does not change in response to the port setting on which this interface is connected, such as switch.

In newer version, this settings can be done in configuration file. For example in newer version SUSE such as 10.x, this setting can be done in respective interface configuration file, which can be found under /etc/sysconfig/network. The interface configuration file looks like ifcfg-eth-id-00:c0:0d:01:75:05

In older versions such as SUSE 9, we need to set up manually. I added this settings in a bash shell script and placed under /etc/sysconfig/network/scripts and created symbolic links from /etc/sysconfig/network/if-up.d.

# ls -al
total 8
drwxr-xr-x 2 root root 4096 Apr 22 2008 .
drwxr-xr-x 6 root root 4096 Feb 19 2008 ..
lrwxrwxrwx 1 root root 21 Apr 22 2008 eth0-setup -> ../scripts/eth0-setup

# cat ../scripts/eth0-setup

#!/bin/bash
#
# This script has been added by Sikkandar to make sure
# that the NIC Configuration is set to FULL DUPLEX with SPEED 100
#
# Date : 04.Oct.2007
#
# OS : SUSE LINUX Enterprise Server 9
#
/usr/sbin/ethtool -s eth0 autoneg off duplex full speed 100

Have Fun ........

Sikkandar.Linux at GMail.Com

What is "/etc/fstab" and how it is important for "mount" command.

2008-12-03T07:14:00.000-08:00

fstab stands for File System Table, contains device or partitions details and indicates how they are to be initialized. This file is mostly used by mount command.

Let us have a look at what each column means on this file:

Sample content of /etc/fstab (on Solaris it is /etc/vfstab)

1st Column (device-name): This column contains devices or partitions name

2nd Column (mount point):Mount point of device or partition

3rd Column (fs-type): The type of file system

4th Column (mount-options): Mount options such as ro, rw, noauto, user, exec and acl, etc. use man

5th Column (dump-frequency): useful when we use dump command for backup larger numbers than one are to avoid too many backups of idle file-systems

6th Column (pass-number): This tells on which order, the fsck to be done while booting. "0" zero means don't do fsck.

Whenever we issue mount -a, it reads the /etc/fstab and mount the file systems according to the settings. If it is "noauto" on mount-options for any file systems, it will not mount. Default is auto.

For more, do a "man mount"

Have a fun ....

Sikkandar.Unix at Gmail.Com

Sendmail - How to Override MX Record

2008-12-01T08:41:00.000-08:00

The following settings force the mails to forward particular server:

1. Add following line into /etc/mail/mailertable

domain mailer:[destinationhost.domain.name]

2. rebuild mailertable

makemap hash mailertable < mailertable

3. restart sendmail

rcsendmail restart

Sendmail - How to process mail from mail queue for particular Email Address

2008-12-01T08:37:00.000-08:00

sendmail -q -v -qREmailID@domain.name

Example: sendmail -q -v -qRnsikkandar@gmail.com

sendmail - How to reprocess mail from mail queue for particular domain

2008-12-01T08:08:00.000-08:00

sendmail -q -v -qR@valid.domain.name

Example:

sendmail -q -v -qR@gmail.com
sendmail -q -v -qR@my.example.com

Installing Windows 2000 on Dell Power Edge 2950

2008-11-10T09:34:00.001-08:00

I had a chance to install Windows 2000 on Dell power Edge 2950. I created the RAIDs using Adaptech utilities and started installation through CD-ROM. But, unfortunately the OS could not see the Disk arrays and thrown following error:

There is no disk in this drive

So, the installation aborted. Then I tried the installation once again using Windows 2000 installation CD, and pressed F6 to load drivers. But it is asking to load Floppy disk to load drivers. But, Dell Power Edge 2950 does not have Floppy drive, the installation started consuming time. Now, we have to either make the USB drive as Floppy drive or integrate OS with Perc-5 drivers.

Fortunately, our windows admin integrated the Perc-5 with Windows 2000 CD with the help of utility provided by IBM, the installation started smoothly.

Hope, IBM and Windows will resolve this issue soon and make the administrator to have deep breath :-)

Have a fun guys.
sikkandar.unix at gmail.com
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Topics will be covered in this Blog are : Linux System Administrator - Memory Performance Tuning - File System - User Group - Linux / Unix Commands Processes - Virtual Swap Memory - Mail Server - Remote Access - Linux Permissions - Boot procedure system Logging - Network (xinetd) Configuration (ifconfig) - DNS - DHCP - Web Server - Kernel - Shell Script - Tuning Optimization High Availability Heart-BeatClustering-Backup and Recovery - Network Time Protocol - NIS - NFS - RPM Partition - /proc - Scheduling (crontab) - mount unmount - secured shell (ssh) - Remote Access - Virtual Network Computing (VNC) Default Ports - Services
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IPSO Installation on Nokia Firewall and CheckPoint Installation on Nokia Firewall

2008-10-24T08:38:00.001-07:00

My First experience on Nokia Firewall :-). I wanted this to be documented, may useful for others too. Let me know if you have any feedback.

Installing IPSO on Nokia IP330 through FTP

Pre-Install

Connect IP330 with your machine through console cable on COM port.
Connect Nokia IP330 with your machine through cross over cable (or make both the machine in same network and provide concern gateway)

Create a Hyper Terminal

Provide a name for a connection and select Icon and click OK

Select COM Port on which the console cable is connected from Nokia IP330, (COM1 is in this example) and click OK

Click Restore Defaults and click OK

Now Power ON the Nokia IP330 device, you should able to see the basic booting messages, wait till you get the following options :

1. Boot Manager
2. IPSO

Press 1

On boot manager command, type "install" and provide the required information when asked.
Basically it asks, type of FTP Connection (Make sure, FTP is running on your machine and Firewall is off, and the gate way is the IP you are going to assign for your Nokia IP330. Make ftp home directory as where IPSO CD is loaded), IP Address of Nokia Device and FTP IP address, and Speed/Duplex settings, etc.

You will be prompted with three options

1. Install all packages without prompt
2. Install all packages with prompt
3. No packages

We select option 3 so that only IPSO will be installed.

Once installation is completed, reboot the machine and provide the required data when it prompts.

Now you should able to open GUI (Voyager) from your machine through browser with the IP assigned for Nokia IP330 and you can able to manage your Nokia IP330

INSTALLAING CHECKPOINT THROUGH VOYAGER)

1. Download IPSO Wrapper from CheckPoint site and store it into your ftp home folder
2. Open Voyager GUI through browser and login with admin id and password
3. Goto Manage installed packages - FTP and new packages - provide FTP server IP, user id and password and Finally click Apply
4. It will extract the wrapper. Now install the wrapper. You may watch the status in console by seeing online log file which is located in /var/log/ (tail -f /var/log/newpkg.log)
5. restart machine or relogin (su -).
6. Restart CheckPoint "cpstop" and "cpstart" from /opt/CPshared-50-04/bin
7. Now run cpconfig from console from /opt/CPshared-50-04/bin
8. Provide all required details when prompts. Usually, License details, Management stations IP, GUI Enable, and Admin users, etc....
9. Install Checkpoint Client (Smart Center) on Management station and connect to the Nokia IP330 Firewall.
10. Make necessary settings and rules according to your company policies.

Have lot of fun ......

Sikkandar dot linux at Gmail.Com

Recover Corrupted Partition From A Bad Superblock

2008-10-15T14:50:00.000-07:00

1. Find a backup superblock using newfs command

Example

newfs -N /dev/sda2

OR

dumpe2fs /dev/sda2 | grep superblock

2. Now you have the superblock (if you are lucky). Recover the superblock.

fsck -b /dev/sda2

Example

fsck -b 32768 /dev/sda2

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Topics will be covered in this Blog are : Linux System Administrator - Memory Performance Tuning - File System - User Group - Linux / Unix Commands Processes - Virtual Swap Memory - Mail Server - Remote Access - Linux Permissions - Boot procedure system Logging - Network (xinetd) Configuration (ifconfig) - DNS - DHCP - Web Server - Kernel - Shell Script - Tuning Optimization High Availability Heart-BeatClustering-Backup and Recovery - Network Time Protocol - NIS - NFS - RPM Partition - /proc - Scheduling (crontab) - mount unmount - secured shell (ssh) - Remote Access - Virtual Network Computing (VNC) Default Ports - Services
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2008-09-15T14:06:00.000-07:00

<br />How to use ssh without asking password? <br />
How to use ssh without asking password?

We may need to login to other servers or our script may need to collect data from other servers. As we know, ssh is a secured connection to the remote servers and we may need to login without password. Here are the steps to use ssh login without password:

aspadmin is an existing user in both "LinuxMonitor" and "mail1" servers.

Step-1: Generating Keys:

aspadmin@LinuxMonitor:~> ssh-keygen -t rsa

Generating public/private rsa key pair.
Enter file in which to save the key (/home/aspadmin/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/aspadmin/.ssh/id_rsa.
Your public key has been saved in /home/aspadmin/.ssh/id_rsa.pub.
The key fingerprint is:
24:bf:71:70:ba:72:39:76:3e:a7:1c:bc:81:c3:92:f5 aspadmin@LinuxMonitor

Step-2: Creating ".ssh" folder in remote machine(mail1) for user(aspadmin)

aspadmin@LinuxMonitor:~> ssh aspadmin@mail1 mkdir -p .ssh

The authenticity of host 'mail1' can't be established.
RSA key fingerprint is 8b:2a:08:a9:89:8d:8e:31:25:0a:dd:77:d5:7f:30:e0.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'mail1,' (RSA) to the list of known hosts.
Password:

Step-3: Copying the key to the remote machine(mail1) for user(aspadmin)

aspadmin@LinuxMonitor:~> scp .ssh/id_rsa.pub aspadmin@mail1:~aspadmin/.ssh/authorized_keys2

Password:
id_rsa.pub 100% 231 0.2KB/s 00:00

Step-4: Thats all. Now you can connect to mail1 without password.

aspadmin@LinuxMonitor:~> ssh mail1

Last login: Wed Jun 25 14:51:52 2008 from xxx
aspadmin@mail1:~>

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Topics will be covered in this Blog are : Linux System Administrator - Memory Performance Tuning - File System - User Group - Linux / Unix Commands Processes - Virtual Swap Memory - Mail Server - Remote Access - Linux Permissions - Boot procedure system Logging - Network (xinetd) Configuration (ifconfig) - DNS - DHCP - Web Server - Kernel - Shell Script - Tuning Optimization High Availability Heart-BeatClustering-Backup and Recovery - Network Time Protocol - NIS - NFS - RPM Partition - /proc - Scheduling (crontab) - mount unmount - secured shell (ssh) - Remote Access - Virtual Network Computing (VNC) Default Ports - Services
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How to configure xinetd?

2008-09-13T15:29:00.000-07:00

xinetd Daemon

By default xinetd does not start automatically. You can find this service under /etc/init.d. To make xinetd daemon to start start automatically during boot, run insserv xinetd (or) chkconfig xinetd on

To start/stop/restart/reload xinetd, use rcxinetd command

Configuration

/etc/xinetd.conf is a default configuration file of xinetd. You may not need to make any changes in this file.

You can include dedicated configuration file for each service under /etc/xinetd.d folder.
Example configuration file for pop3

service pop3
{
port = 110
socket_type = stream
protocol = tcp
wait = no
user = root
server = /usr/sbin/popper
}

Few useful options are below:

instances = 30 #Maximum number of instaances
cps = 50 10 #50 connections per seconds, 10 seconds wait time after 50 connections.
only_from #allow from specific remote hosts
no_access #restrict access for specific remote hosts
access_time #service available time e.g. access_time 09:00-20:00
interface #specify which IP being used for xinetd when more than one interface used.

For more information man xinetd
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Topics will be covered in this Blog are : Linux System Administrator - Memory Performance Tuning - File System - User Group - Linux / Unix Commands Processes - Virtual Swap Memory - Mail Server - Remote Access - Linux Permissions - Boot procedure system Logging - Network (xinetd) Configuration (ifconfig) - DNS - DHCP - Web Server - Kernel - Shell Script - Tuning Optimization High Availability Heart-BeatClustering-Backup and Recovery - Network Time Protocol - NIS - NFS - RPM Partition - /proc - Scheduling (crontab) - mount unmount - secured shell (ssh) - Remote Access - Virtual Network Computing (VNC) Default Ports - Services
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why xinetd

2008-09-13T15:20:00.000-07:00

The services can be fired when the system boots, which will occupy its respective ports and waiting for connections always. It will be using resources un-necessarily if the services will be used occasionally.

xinetd process run behalf of the services and it starts the process if any connection comes. So, it saves more system resources.

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Topics will be covered in this Blog are : Linux System Administrator - Memory Performance Tuning - File System - User Group - Linux / Unix Commands Processes - Virtual Swap Memory - Mail Server - Remote Access - Linux Permissions - Boot procedure system Logging - Network (xinetd) Configuration (ifconfig) - DNS - DHCP - Web Server - Kernel - Shell Script - Tuning Optimization High Availability Heart-BeatClustering-Backup and Recovery - Network Time Protocol - NIS - NFS - RPM Partition - /proc - Scheduling (crontab) - mount unmount - secured shell (ssh) - Remote Access - Virtual Network Computing (VNC) Default Ports - Services
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How to check Network speed (Bandwidth / throughput) between servers

2008-06-14T09:15:00.000-07:00

One of the best tool I used to check network (bandwidth / throughput) speed is, iperf. The easiest way to install iperf is just google for iperf RPM, download appropriate rpm for your server.

You donot have to be an expert to run iperf. once iperf is installed in your server, just run iperf -s in the server and iperf -c ServerIP in client. Thats all, you will get the result. iperf is having many options to investigate your network performance.

For example:

At Server
=======

iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 32.00 KByte (default)
------------------------------------------------------------

At Client
======

iperf -c 10.0.0.5
------------------------------------------------------------
Client connecting to 10.0.0.5, TCP port 5001
TCP window size: 32.00 KByte (default)
------------------------------------------------------------
[1912] local 10.0.0.211 port 1793 connected with 10.0.0.5 port 5001
[ ID] Interval Transfer Bandwidth
[1912] 0.0-10.0 sec 103 MBytes 94 Mbits/sec

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Topics will be covered in this Blog are : Linux System Administrator - Memory Performance Tuning - File System - User Group - Linux / Unix Commands Processes - Virtual Swap Memory - Mail Server - Remote Access - Linux Permissions - Boot procedure system Logging - Network (xinetd) Configuration (ifconfig) - DNS - DHCP - Web Server - Kernel - Shell Script - Tuning Optimization High Availability Heart-BeatClustering-Backup and Recovery - Network Time Protocol - NIS - NFS - RPM Partition - /proc - Scheduling (crontab) - mount unmount - secured shell (ssh) - Remote Access - Virtual Network Computing (VNC) Default Ports - Services
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Linux Commands

2008-05-11T10:13:00.000-07:00

accept
access
aclocal
aconnect
acpi
acpi_available
acpid
addr2line
addresses
agetty
alsactl
amidi
amixer
anacron
aplay
aplaymidi
apm
apmd
apropos
apt
ar
arch
arecord
arecordmidi
arp
as
at
atd
atq
atrm
audiosend
aumix
autoconf
autoheader
automake
autoreconf
autoscan
autoupdate

badblocks
banner
basename
bash
batch
bc
biff
bison
bzcmp
bzdiff
bzgrep
bzip2
bzless
bzmore

c++
c++filt
cal
cardctl
cardmgr
cat
cc
cdda2wav
cdparanoia
cdrdao
cdrecord
cfdisk
chage
chattr
chfn
chgrp
chkconfig
chmod
chown
chpasswd
chroot
chrt
chsh
chvt
cksum
clear
cmp
col
colcrt
colrm
column
comm
compress
cp
cpio
cpp
crond
crontab
csplit
ctags
cupsd
cut
cvs

date
dd
deallocvt
debugfs
depmod
devdump
df
diff
diff3
dig
dir
dircolors
dirname
disable
dlpsh
dmesg
dnsdomainname
dnssec-keygen
dnssec-makekeyset
dnssec-signkey

dnssec-signzone
doexec
domainname
dosfsck
du
dump
dumpe2fs
dumpkeys

e2fsck
e2image
e2label
echo
edquota
egrep
eject
elvtune
emacs
enable
env
envsubst
esd
esd-config
esdcat
esdctl
esddsp
esdmon
esdplay
esdrec
esdsample
etags
ex
expand
expr

factor
false
fc-cache
fc-list
fdformat
fdisk
fetchmail
fgconsole
fgrep
file
find
finger
fingerd
flex
fmt
fold
formail
free
fsck
ftp
ftpd
fuser

g++
gawk
gcc
gdb
getent
getkeycodes
gpasswd
gpg
gpgsplit
gpgv
gpm
gprof
grep
groff
groffer
groupadd
groupdel
groupmod
groups
grpck
grpconv
gs
gunzip
gzexe
gzip

halt
hdparm
head
hexdump
host
hostid
hostname
htdigest
hwclock

iconv
id
ifconfig
imapd
inetd
info
init
insmod
install
ipcrm
ipcs
iptables
iptables-restore
iptables-save
isodump
isoinfo
isosize
isovfy
ispell

join

kbd_mode
kbdrate
kernelversion
kill
killall
killall5
klogd
kudzu

last
lastb
lastlog
ld
ldconfig
ldd
less
lesskey
lftp
lftpget
link
ln
loadkeys
locale
locate
lockfile
logger
login
logname
logrotate
look
losetup
lpadmin
lpinfo
lpmove
lpq
lpr
lprm
lpstat
ls
lsattr
lspci
lsmod
lsusb

m4
mail
mailq
mailstats
mailto
make
makedbm
makemap
man
manpath
mattrib
mbadblocks
mcat
mcd
mcopy
md5sum
mdel, mdeltree
mdir
mdu
merge
mesg
metamail
metasend
mformat
mimencode
minfo
mkdir
mkdosfs
mke2fs
mkfifo
mkfs
mkfs.ext3
mkisofs
mklost+found
mkmanifest
mknod
mkraid
mkswap
mktemp
mlabel
mmd
mmount
mmove
modinfo
modprobe
more
mount
mountd
mpartition
mpg123
mpg321
mrd
mren
mshowfat
mt
mtools
mtoolstest
mtype
mv
mzip

named
namei
nameif
netstat
newaliases
newgrp
newusers
nfsd
nfsstat
nice
nm
nohup
nslookup
nsupdate

objcopy
objdump
od
openvt

passwd
paste
patch
pathchk
perl
pidof
ping
pinky
pmap
portmap
poweroff
pppd
pr
praliases
printenv
printf
ps
ptx
pwck
pwconv
pwd
python

quota
quotacheck
quotaon
quotaoff
quotastats

raidstart
ramsize
ranlib
rarpd
rcp
rdate
rdev
rdist
rdistd
readcd
readelf
readlink
reboot
reject
rename
renice
repquota
reset
resize2fs
restore
rev
rexec
rexecd
richtext
rlogin
rlogind
rm
rmail
rmdir
rmmod
rndc
rootflags
route
routed
rpcgen
rpcinfo
rpm
rsh
rshd
rsync
runlevel
rup
ruptime
rusers
rusersd
rwall
rwho
rwhod

sane-find-scanner
scanadf
scanimage
scp
screen
script
sdiff
sed
sendmail
sensors
seq
setfdprm
setkeycodes
setleds
setmetamode
setquota
setsid
setterm
sftp
sh
sha1sum
showkey
showmount
shred
shutdown
size
skill
slabtop
slattach
sleep
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Linux Access Control List (ACL)

2008-05-11T01:22:00.000-07:00

Linux - How to setup Access Control List (ACL)

Basic Linux permissions are having following limitations:

1. We cannot set more than one entity as the user or group owner of a file.
2. We cannot set permission on a per file or directory basis.

ACL is one of the system to overcome these limitations.

Important Note:

Have a look into /etc/fstab to make sure acl is enabled for the device is mounted. Content of /etc/fstab looks like below if acl is enabled:

#cat /etc/fstab

/dev/hda1 / reiserfs acl,user_xattr 1 1
/dev/hda2 swap swap defaults 0 0
proc /proc proc defaults 0 0
.
.
.

If acl is not added for the device in /etc/fstab, you have to add this option and remount.

setfacl - Setting File Access Control List

Once acl is set for a device, using setfacl command, we can create Access Control List. To make user alexander as trustee for a file somefile do the following:

setfacl -m u:alexander:rwx somefile

In addition to that, to add the group sales as trustee group for the file somefile.

setfacl -m g:sales:rw somefile

This command does not make any difference in file permissions, but add a '+' sign behind the permissions list

getfacl - Setting File Access Control List

getfacl somefile displays the acl to somefile

For more information on these commands man setfacl and man getfac

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Topics will be covered in this Blog are : Linux System Administrator - Memory Performance Tuning - File System - User Group - Linux / Unix Commands Processes - Virtual Swap Memory - Mail Server - Remote Access - Linux Permissions - Boot procedure system Logging - Network (xinetd) Configuration (ifconfig) - DNS - DHCP - Web Server - Kernel - Shell Script - Tuning Optimization High Availability Heart-BeatClustering-Backup and Recovery - Network Time Protocol - NIS - NFS - RPM Partition - /proc - Scheduling (crontab) - mount unmount - secured shell (ssh) - Remote Access - Virtual Network Computing (VNC) Default Ports - Services

Setting Permissions

2008-05-05T12:39:00.000-07:00

Linux works with three entities that can be set as the owner of the file or directory. Those are owner, group owner and others.

ls -l command provide the detailed information of files in a directory. The first column of the output shows 10 permission bits something like -rwxr-xr-x

For example:

# ls -l
-rwxr-xr-x 1 alexander users 1024 2008-05-06 11:20 somefile

(# in above example, is command prompt)

The first bit says the type of the file. Mostly it is - which means it is a regular file. If it is d means, it is a directory and etc.

The next three bits says the permissions (r-read, w-write, x-execute) for owner of the file.

The next three bits says the permissions for the group and last three bits says the permission for others.

The owner of the file or Administrator can change the permission of a file using chmod command.

chmod entity + or - permission(s)

For example, to remove executable permission for others for file somefile

chmod o-x somefile

to add write permission for group for file somefile

chmod g+w somefile

Permissions are

r - read
w - write
x - execute
s - set user or group id
t - sticky bit

If set user or group id is given for a file, the execute (x) permission of respective entity (user or group) will be replaced with s

For example, if set user id is given fo somefile, it looks like below output

-rwsr-xr-x 1 alexander users 1024 2008-05-06 11:20 somefile

If sticky bit is set to a file, t will be added at last bit of permissions

For example, if sticky bit is set to somefile, it looks like below output

-rwsr-xr-t 1 alexander users 1024 2008-05-06 11:20 somefile

Set User ID, Group ID and Sticky Bit

2008-05-05T12:33:00.000-07:00

SUID: Set User ID means, when this permission is applied to the executable file, the user who execute the file will have the permissions of the owner of the file while executing.

SGID: Set Group ID

Sticky Bit: When sticky bit is applied to a file, user can remove only if (1) the user is owner of the file (2) the file is in a directory of which the user is the owner OR (3) the user has the write permissions on the file.

Change Group Ownership

2008-05-04T11:40:00.000-07:00

To check the list of groups a user belongs to ....

groups user

To change the group owner for temporary ...

newgrp groupName

Example:

To see the list of groups the user alexander belongs to ...

groups alexander

To change the primary group of alexander to sales, as user alexander, type below command.

newgrp sales

Changing File Ownership

2008-05-04T10:05:00.000-07:00

chown {user|.group} file

It is a command to change the owner of the file or directory.

For example

(1) to change the owner of file example to alexander

chown alexander example

(2) to change the group owner of file example to development

chown .development example

(3) to change the owner of file example to alexander and group owner to development in one command

chown alexander.developent example

(4) to change the owner of directory example and all its sub-directories to owner alexander.

chown -R alexander example

Note: The option -R means Recursively

Deleting User

2008-05-03T01:26:00.000-07:00

userdel

This is the command to delete user in your local system.

delete an user

userdel sikkandar

User sikkandar will be deleted from your local machine without home directory.

Delete an user with home directory

userdel -r sikkandar

Delete an user with home directory including files owned by other users

userdel -rf sikkandar

Adding New User

2008-04-20T07:21:00.000-07:00

useradd

This is the command to create new user in your local system.

Create an user

useradd sikkandar

User sikkandar will be added to your local machine without home directory.

Create an user with home directory

useradd -m sikkandar

To create password for user

passwd username

For example: passwd sikkandar

For more details see man useradd

TIPS

If you forgot to create home directory and you want to create the same later, do the following:

To create the home directory for user sikkandar:

mkdir /home/sikkandar
cd /etc/skel
tar cv . | tar xvC /home/sikkandar
chown -R sikkandar.users /home/sikkandar

Checking NTP Synchronization Status

2008-04-20T06:32:00.000-07:00

ntpq -p provides the current NTP synchronization status.

Network Time Protocol (NTP) - Client Configuration

2008-04-20T06:00:00.000-07:00

Step-1

Check the time difference between the NTP server and Client. If the time difference is more than 1024 seconds, run ntpdate (ntpdate synchronize the time with the server) command as follows:

ntpdate ntp.your-ntp-server.somewhere

For example: ntpdate pool.ntp.org

IMPORTANT NOTE:

You may get an Error message "socket already in use" while running ntpdate command. You will get this error if xntpd is running already in your machine, most probably. So stop xntpd (rcxntp stop) running ntpdate.

Step-2

Add

server ntp.your-ntp-server.somewhere

to NTP Configuration file i.e. /etc/ntp.conf

For Example:

server pool.ntp.org

Step-3

Run rcxntpd restart command.