TIP: Immutable files

[mynameistmp]

In the ext2 and ext3 filesystems there are a number of additional file attributes available that are beyond the standard bits accessible by chmod. Here is an example of a neat one:

sh-3.00$ cat test.txt; ls -l test.txt; id
x86
-rw-r--r--  1 tmp users 4 2005-09-19 00:33 test.txt
uid=1000(tmp) gid=100(users) groups=100(users),11(floppy),17(audio),18(video),19(cdrom)
sh-3.00$ rm -f test.txt
rm: cannot remove `test.txt': Operation not permitted

Seems strange. It's a typical text file. My UID is the owner of this file, but I can't delete it. Alright, let's try with root:

root@tmp:/home/tmp# id ; rm -f test.txt
uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel),11(floppy)
rm: cannot remove `test.txt': Operation not permitted

The problem is that this file is 'immutable'. For those of you who aren't familiar with this you should check out the man page on lsattr and chattr. All we need to do is get rid of the immutable attribute and we're off to the races:

root@tmp:/home/tmp# lsattr test.txt
----i-------- test.txt
root@tmp:/home/tmp# chattr -i test.txt
root@tmp:/home/tmp# rm test.txt

While this flag is set any attempts to unlink, overwrite, rename, or append to the file will fail.

[Newby]

That's awesome. Thanks for the tip. :)

[Sidoh]

Indeed!  Thanks, tmp.  :)

[Quik]

Hrm, was curious how you did this. Might be helpful.

[mfqr]

cool tip :). thanks.