You would set the sticky bit primarily on directories in UNIX / Linux.
If you set the sticky bit to a directory, other users cannot delete or rename the files (or subdirectories) within that directory.
When the sticky bit is set on a directory, only the owner and the root user can delete / rename the files or directories within that directory.
1. Set the sticky bit on Directory
The example below enables the sticky bit on a directory.
Use chmod command to set the sticky bit. If you are using the octal numbers in chmod, give 1 before you specify other numbered privileges, as shown below. The example below, gives rwx permission to user, group and others (and also adds the sticky bit to the directory).
$ chmod 1777 dir
Or, you can assign only sticky bit to an existing directory (without touching any other user, group and other privileges) using chmod command as shown below.
$ chmod +t dir
Once the sticky bit is assigned to a directory, you’ll see (t) as the last character in the permission. In this example, it is drwxrwxrwt.
$ ls -ld /home/bala/dir drwxrwxrwt 2 bala bala 4096 2011-01-28 14:09 /home/bala/dir $ ls -l dir total 8 -rwxrwxrwx 1 bala bala 20 2011-01-28 14:12 bala.txt -rwxrwxrwx 1 guest guest 41 2011-01-28 14:13 guest.txt
In the above example, as dir has rwx permission to everybody, all other users are allowed to do create their files or directories under this directory. However, even when the sub-directories or files under dir is having rwx permission to everybody, only the owner of those can delete or rename those files and directory. Other users cannot delete or rename it because of sticky bit.
In the above example, bala.txt has rwx to users, groups, and others. But, when guest user is trying to delete the file bala.txt, he’ll see the “Operation not permission” message as shown below.
$ su guest Password: $ cd /home/bala/dir1 $ rm bala.txt rm: cannot remove `bala.txt': Operation not permitted
Please note that /tmp has sticky bit enabled by default. You might have not noticed that until now. Now you know why /tmp directory is supposed to have sticky bit enabled.
$ ls -ld /tmp drwxrwxrwt 3 root root 4096 Jan 31 08:29 /tmp
To remove the sticky bit from a directory, do the following.
$ chmod -t dir
2. Set the sticky bit on File
Setting the sticky bit on a file is pretty much useless, and it doesn’t do anything. On some of the older *nix flavors, a sticky bit enabled executable file will be loaded to the swap memory after 1st execution, which speeds up all subsequent execution. This is not true anymore.
Currently, this behavior is only operative in HP-UX, NetBSD, and UnixWare. Solaris appears to have abandoned this in 2005. The 4.4-Lite release of BSD retained the old sticky bit behavior but it has been subsequently dropped from OpenBSD (as of release 3.7) and FreeBSD (as of release 2.2.1); it remains in NetBSD. No version of Linux has ever supported the traditional behavior.
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