trouble with file permission

[Jan Hawes_2]

Hello,

I found a effect which i really don't understand.

Using user1:
- touch test_file
- chmod 400 test_file

Using user2:
- rm test_file

-> files is deleted

Why is user2 able to delete the testfile?

They have the same gid, but not the same uid.

I don`t understand, can you help me?

bye jan

[James Specht]

This would happen if the directory permissions allowed the group or others read/write access to the files within. /tmp is a good example with its 777 mode.

--Jim

[Vitek Pepas]

In order to protect the file against removal you would have to change directory permissions. Set the sticky bit to make sure only owner can remove the file.

[Thierry Poels_1 · Accepted solution]

hi,

file deletion privileges are controled by the directory privileges (you are writing in the directory if you delete a file).

So if user2 cannot write into this directory he cannot remove the file.
Otherwise use the sticky bit (chmod +t /dir), then only root, directory owner & file owner can remove a file.

regards,
Thierry Poels.

[Sanjay_6]

Hi Jan,

The other user "user2" is able to delete the file owned by "user1" even if the file has 400 permissions is because the directory in which the file is located is writable by user2. Since the users have the same GID's the directory is writable by either group or world or both.

Hope this helps.

Regds