Thursday, March 24, 2011

Inodes Linux /Unix

=> File type (executable, block special etc)
=> Permissions (read, write etc)
=> Owner
=> Group
=> File Size
=> File access, change and modification time (remember UNIX or Linux never stores file creation time, this is favorite question asked in UNIX/Linux sys admin job interview)
=> File deletion time
=> Number of links (soft/hard)
=> Extended attribute such as append only or no one can delete file including root user (immutability)
=> Access Control List (ACLs)
Each inode is identified by a unique inode number within the file system. Inode is also know as index number.

How do I see file inode number?

[root@rajat Desktop]# stat Amazon\ Web\ Services.pdf 
  File: `Amazon Web Services.pdf'
  Size: 1968423   Blocks: 3848       IO Block: 4096   regular file
Device: 803h/2051d Inode: 262327      Links: 1
Access: (0644/-rw-r--r--)  Uid: (  500/   rajat)   Gid: (  500/   rajat)
Access: 2011-03-25 10:22:30.192428487 +0530
Modify: 2010-06-01 00:34:44.000000000 +0530
Change: 2011-03-21 23:20:08.933990061 +0530

[root@rajat Desktop]#ls -i Amazon\ Web\ Services.pdf 
262327 Amazon Web Services.pdf 

Zombie Process Linux

A process can be sleeping in kernel code. Usually that's because of faulty hardware or a badly written driver- or maybe a little of both. A device that isn't set to the interrupt the driver thinks it is can cause this, for example- the driver is waiting for something its never going to get. The process doesn't ignore your signal- it just never gets it.
A zombie process doesn't react to signals because it's not really a process at all- it's just what's left over after it died. What's supposed to happen is that its parent process was to issue a "wait()" to collect the information about its exit. If the parent doesn't (programming error or just bad programming), you get a zombie. The zombie will go away if its parent dies- it will be "adopted" by init which will do the wait()- so if you see one hanging about, check its parent; if it is init, it will be gone soon, if not the only recourse is to kill the parent..which you may or may not want to do.
* Finally, a process that is being traced (by a debugger, for example) won't react to the KILL either.

We can find out zombie process by :-
Use top or ps command:

# top
# ps aux | awk '{ print $8 " " $2 }' | grep -w Z

#ps -el | grep Z

How do I kill zombie process?
You cannot kill zombies, as they are already dead. But if you have too many zombies then kill parent process or restart service.

You can kill zombie process using PID obtained from any one of the above command. For example kill zombie proces having PID 4104:
# kill -9 4104
*Please note that kill -9 does not guarantee to kill a zombie process

How do I automate zombie process killing?
Write a script and schedule as a cron job.

 `ps jauxww | grep Z | grep -v PID | awk ‘{print $3}’`; do for every in `ps auxw | grep $each | grep cron | awk ‘{print $2}’`; do kill -9 $every; done; done

Wednesday, March 23, 2011

Firefox 4 for fedora 14

#vi /etc/yum.repos.d/firefox.repo

# Place this file in your /etc/yum.repos.d/ directory

name=Firefox 4 Web Browser

[root@rajat yum.repos.d]# yum install firefox4
Loaded plugins: langpacks, presto, refresh-packagekit
Adding en_US to language list
fedora-firefox4                                          | 3.0 kB     00:00     
fedora-firefox4/primary_db                               |  15 kB     00:00     
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package firefox4.i686 0:4.0-2.fc14 set to be installed
--> Processing Dependency: gecko-libs(x86-32) = 2.0-1 for package: firefox4-4.0-2.fc14.i686
--> Processing Dependency: for package: firefox4-4.0-2.fc14.i686
--> Running transaction check
---> Package xulrunner2.i686 0:2.0-1.fc14 set to be installed
--> Processing Dependency: sqlite >= 3.7.4 for package: xulrunner2-2.0-1.fc14.i686
--> Running transaction check
---> Package sqlite.i686 0:3.7.4-1.fc14 set to be updated
--> Finished Dependency Resolution

Dependencies Resolved

 Package           Arch        Version             Repository              Size
 firefox4          i686        4.0-2.fc14          fedora-firefox4         17 M
Installing for dependencies:
 xulrunner2        i686        2.0-1.fc14          fedora-firefox4        8.7 M
Updating for dependencies:
 sqlite            i686        3.7.4-1.fc14        fedora-firefox4        329 k

Transaction Summary
Install       2 Package(s)
Upgrade       1 Package(s)

Total download size: 26 M
Is this ok [y/N]: y
Downloading Packages:
Setting up and reading Presto delta metadata
fedora-firefox4/prestodelta                              | 8.9 kB     00:00     
Processing delta metadata
Package(s) data still to download: 26 M
(1/3): firefox4-4.0-2.fc14.i686.rpm                      |  17 MB     18:54     
(2/3): sqlite-3.7.4-1.fc14.i686.rpm                      | 329 kB     00:18     
(3/3): xulrunner2-2.0-1.fc14.i686.rpm                    | 8.7 MB     08:43     
Total                                            16 kB/s |  26 MB     28:01     
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Updating       : sqlite-3.7.4-1.fc14.i686                                 1/4 
  Installing     : xulrunner2-2.0-1.fc14.i686                               2/4 
  Installing     : firefox4-4.0-2.fc14.i686                                 3/4 
  Cleanup        : sqlite-                              4/4 

  firefox4.i686 0:4.0-2.fc14                                                    

Dependency Installed:
  xulrunner2.i686 0:2.0-1.fc14                                                  

Dependency Updated:
  sqlite.i686 0:3.7.4-1.fc14                                                    

[root@rajat yum.repos.d]# 



Wednesday, March 16, 2011

Enable Quota on RHEL/CentOS

Quota is used for limiting the disk usage for users or groups.

###To verify that the quota is enabled in the kernel###
#grep CONFIG_QUOTA /boot/config-`uname -r`
[root@rajat rajat]#

Create user :
#useradd rajat
#passwd latar

Edit /etc/fstab :
From :
/dev/sda5 /home ext3 defaults 1 2
To :
/dev/sda5 /home ext3 defaults,usrquota,grpquota 1 2

Remount the disk (make sure it’s not in use) :
#mount -o remount /home

Check if usrquota and grpquota are enabled :
#mount | grep /home

Create quota files :
#quotacheck -cvug /home

This creates /home/aquota.user and /home/

Check quota :
#quotacheck -avug

Enable quota for user1 :

#edquota user1
Edit soft and hard limits (1000 = 1 MB) or inode values.

Check the quota for user1 :
#quota user1

Enable quota :
#quotaon -avug

In addition :

Through a cron, run everynight when the filesystem is not used :
#quotaoff -avug && quotacheck -avug && quotaon --avug

Get quota stats :
#repquota -a