what-is-inodes-in-linux

What is Inodes in Linux

what-is-inodes-in-linux

Inode in Linux ?

what is inode in linux and unix ?. inode normally referred as Index Node. inode is layout structure in a unix based file system which describes file system object like files and directories.

Every inode contains attributes and disk block target location of the file or directory. Inode include metadata of file system attributes like time of last change, time of last access, time of last modification, file ownership details, file permission details.

It can be treated as directories are lists of names assigned to inodes. Directory always contains entry for itself, parent and its children.

You might have seen while creating any new file system in linux. inodes gets created at that time of new file system creation when using mkfs command.

Number of inodes depends upon file system size because inode size depends upon block size.You also might have faced situation when inodes gets full even file system have enough free space.

For example mail system like sendmail or postfix creates too many files and it fills up inodes of the file system.No more files gets created or updated and have good chance application to fail as it have no space to write any data.

Normally mail system creates too many files in /var/spool/clientmqueue directory.Logically it happens because if any inode consume one block of disk .

Normally 512 bytes block even inode size is anything below 512 bytes but it will not hold any other data.

Linux and Unix  both use similar inode concepts.This was few details about what  is inode in linux. Let us see how we can check inode in linux and unix.

How to check inode in linux

Procedure for how to check inode in linux is as below.ls,df,stat command is really helpful in getting details of inodes in linux. 
Few example has been displayed below which might be helpful to understand.

[[email protected] ~]# stat passwd |grep Inode
Device: 802h/2050d      Inode: 1193625     Links: 1
[[email protected] ~]# ls -i passwd
1193625 passwd
[[email protected] ~]# ls -ai passwd
1193625 passwd
[[email protected] ~]# df -ih
Filesystem                    Inodes IUsed IFree IUse% Mounted on
/dev/sda2                    1.3M  149K  1.2M   12% /
devtmpfs                     4.0M   455  4.0M    1% /dev
tmpfs                          4.0M     1  4.0M    1% /dev/shm
tmpfs                          4.0M   884  4.0M    1% /run
tmpfs                          4.0M    16  4.0M    1% /sys/fs/cgroup
/dev/sda1                    126K   349  125K    1% /boot
/dev/sda3                    513K   13K  501K    3% /var
/dev/sda5                    256K   106  256K    1% /tmp
/dev/sda6                    256K   735  256K    1% /var/log
/dev/sda7                    128K    16  128K    1% /var/log/audit
[[email protected] ~]#$ stat /var
File: â/varâ
Size: 4096            Blocks: 8          IO Block: 4096   directory
Device: 803h/2051d      Inode: 2           Links: 28
Access: (0755/drwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2020-01-10 02:08:14.851047321 -0500
Modify: 2019-10-31 01:51:52.137319406 -0400
Change: 2019-10-31 01:51:52.137319406 -0400
Birth: -
[[email protected] ~]# df -i /var
Filesystem  Inodes IUsed IFree  IUse% Mounted on
/dev/sda5   525200 9159  516041 2%   /var

How to check inode in unix

Process for how to check inodes in unix is as below.

[[email protected] ~]# df -oi /var
Filesystem                   iused   ifree    %iused Mounted on
/dev/vx/dsk/bootdg/var 52637 943267 5%      /var

So now we have fair idea how to check inode in linux .This might be really helpful in case if you get inode full case.

If you see file system usage and if it is not filled it must be because of inodes are exhausted.You can validate this from messages file with message like no space left on device .

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That,s it about what is inode in linux  .I hope you like it and it must have given some clarity regarding concept of inode.

 

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