Colocation to Virtualization

Inodes “Part 1″ went into locating filesystem level inode information. Here we will move from the main filesystem to the individual file. Besides reviewing how the inode record reflects permissions modification using chown, file removal based on inode number will be covered.

Create a test file

user01@testsrv:~$ touch testfile

Below, “ls” is used to display the inode number (2009418) of the test file

user01@testsrv:~$ ls -i /home/user01/testfile
2009418 /home/user01/testfile
Check the inode record for the newly created empty file

user01@testsrv:~$ stat /home/user01/testfile
File: `/home/user01/testfile'
Size: 0         	Blocks: 0          IO Block: 4096   regular empty file
Device: fe01h/65025d	Inode: 2009418     Links: 1
Access: (0644/-rw-r--r--)  Uid: ( 1000/user01)   Gid: ( 1000/user01)
Access: 2009-04-10 17:52:59.000000000 -0400
Modify: 2009-04-10 17:52:58.000000000 -0400
Change: 2009-04-10 17:52:58.000000000 -0400

In the following example, a file is being checked that is solely owned by the root user

user01@testsrv:~$ ls -la /home/user01/w2k3-2.iso
-rw-r--r-- 1 root root 171769856 2009-03-28 13:15 /home/user01/w2k3-2.iso

Review the root owned ISO file inode information. The user and group ownership is referenced as Uid and Gid respectively

user01@testsrv:~$ stat /home/user01/w2k3-2.iso
File: `/home/user01/w2k3-2.iso'
Size: 171769856 	Blocks: 335824     IO Block: 4096   regular file
Device: fe01h/65025d	Inode: 2009538     Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2009-03-28 13:11:44.000000000 -0400
Modify: 2009-03-28 13:15:33.000000000 -0400
Change: 2009-03-28 13:15:33.000000000 -0400

Change the permissions of the ISO file via the root user (current owner of the file)

root@testsrv:/home/user01# chown user01:user01 /home/user01/w2k3-2.iso

Re-check tje ISO file permission from the initial user (user01) via the ls command

user01@testsrv:~$ ls -la /home/user01/w2k3-2.iso
-rw-r--r-- 1 user01 user01 171769856 2009-03-28 13:15 /home/user01/w2k3-2.iso

Re-stat the ISO file to view the changes in the inode record. As you can see, the file ownership is now set to user user01 and group user01

user01@testsrv:~$ stat /home/user01/w2k3-2.iso
File: `/home/user01/w2k3-2.iso'
Size: 171769856 	Blocks: 335824     IO Block: 4096   regular file
Device: fe01h/65025d	Inode: 2009538     Links: 1
Access: (0644/-rw-r--r--)  Uid: ( 1000/user01)   Gid: ( 1000/user01)
Access: 2009-03-28 13:11:44.000000000 -0400
Modify: 2009-03-28 13:15:33.000000000 -0400
Change: 2009-04-10 17:57:35.000000000 -0400

For the next example user01 is kept as the user, but the group is changed to ‘admin’. Since the current user user01 now has full rights to the file, it can be done from that account

user01@testsrv:~$ chown :admin /home/user01/w2k3-2.iso

Re-stat the file once more to see if the group (Gid) has been changed in the inode for this file

user01@testsrv:~$ stat /home/user01/w2k3-2.iso
File: `/home/user01/w2k3-2.iso'
Size: 171769856 	Blocks: 335824     IO Block: 4096   regular file
Device: fe01h/65025d	Inode: 2009538     Links: 1
Access: (0644/-rw-r--r--)  Uid: ( 1000/user01)   Gid: (  119/   admin)
Access: 2009-03-28 13:11:44.000000000 -0400
Modify: 2009-03-28 13:15:33.000000000 -0400
Change: 2009-04-10 18:00:32.000000000 -0400

Now with the basic understanding of finding an retrieving inode numbers and information, we will proceed to removing files using the “rm” command. Specifically, the following will detail how to remove a file by referencing the inode number. All of which is done by using “find” and passing the results to “rm”.

There have only been a few occasions that I can remember where I have needed to know the following, but it is worth knowing! The main benefit is when a file has been created with a control character in the name

Create a test file

user01@testsrv:/tmp/testdir$ touch '`'
user01@testsrv:/tmp/testdir$ ls
`

Try to remove the file without enclosing the “`” filename

user01@testsrv:/tmp/testdir$ rm `
>

Above you can see that the command did not work. Instead it dropped to the “>” sub-prompt

Locate the inode number for the “`” file. Tab based auto-complete does wonders escaping the special character filename on the command line

user01@testsrv:/tmp/testdir$ ls -i /tmp/testdir/`
1163285 /tmp/testdir/`

Now that the inode number is known, the “find” command can be used to retrieve the filename associated with it

user01@testsrv:/tmp/testdir$ find /tmp -inum 1163285
/tmp/testdir/`

Putting it all together, we can remove the file passing the “find” results to “rm”. Below uses a command line pipe (“|”) and xargs to accomplish this

user01@testsrv:/tmp/testdir$ find /tmp -inum 1163285 | xargs rm

Verify the file has been removed

user01@testsrv:/tmp/testdir$ ls /tmp/testdir/

The same can be accomplished via find commands built-in exec feature

user01@testsrv:/tmp/testdir$ find /tmp -inum 1163285 -exec rm {} ;

In my opinion, the best way to remove a file via the inode number is as follows

user01@testsrv:~$ find /tmp -inum 1163285 -exec rm -i {} ;
rm: remove regular empty file `/tmp/testdir/`'? y

Specifying “-i” after rm makes the user verify the file to be removed.

Notes: There are other ways around removing files with certain characters. In this chase, the “`” file could have been removed with:

user01@testsrv:/tmp/testdir$ rm /tmp/testdir/`

If any information in this post is found to be outdated, incorrect, useful, or needs further detail, please leave a comment or email me.