Sticky bit is a
bit set in permission of a file or directory to give special access –rights to
user. When we set the sticky bit for any
executable file, it will remain in swap space after the process exited. It
will help to reduce time of execution in repeatedly used programs. So, we can
set this sticky bit for frequently used programs like editors, commands etc.
So, execution of them will be faster as compared to without sticky bit.
Main important use of sticky
bit is on directory, when we set sticky bit for directory then files reside
in the directory can delete or rename by owner only. This is helpful not to
give access for renaming or deletion to unauthorized user. When sticky bit is
not set for directory then any user having permission to write and execute on
directory can rename and delete files inside the directory.
Sticky bit behavior or feature changes as per operating
system. Linux Kernel ignores the sticky bit on files, it considers only on
directories. In HP-UX work on sticky bit as above mentioned. In AIX, if we set
the sticky bit for directory then only owner can link or unlink the directory
or files specified in the directory.
How to set Sticky bit
on file/directory in Linux?
We will set sticky bit by chmod command. For this purpose, we can use octal mode or by its
symbol ‘t’. lets go through the example.
//Check the permissions of directory sticky
redhat@localhost:~/mywork$ ls -l
total 4
drwxr-xr-x 2 redhat
adm 4096 2013-10-24 15:36 sticky
redhat@localhost:~/mywork$
ls
-l sticky/ //inside directory permissions
total 8
-rwxr-xr-x 1 redhat
adm 57 2013-10-24 15:35 stickybit.sh
-rwxr-xr-x 1 redhat
adm 57 2013-10-24 15:36 stickybit.sh_bak
//Adding sticky bit in permission by below syntax
..or use - chmod 1755 sticky
redhat@localhost:~/mywork$
chmod
+t sticky/
redhat@localhost:~/mywork$
ls
-l sticky/
total 8
-rwxr-xr-x 1 redhat
adm 57 2013-10-24 15:35 stickybit.sh
-rwxr-xr-x 1 redhat
adm 57 2013-10-24 15:36 stickybit.sh_bak
redhat@localhost:~/mywork$
ls
-l
total 4
drwxr-xr-t
2 redhat adm 4096 2013-10-24 15:36 sticky
//In above line sticky bit added in permissions
redhat@localhost:~/mywork$
|
Now we have set the sticky bit to directory. Now we will try
to remove file or script inside the directory.
//Changing the user. Sandeep and redhat having same
group.
redhat@localhost:~/mywork/sticky$
su -
Sandeep
Password:
Sandeep@localhost:~$
Sandeep@localhost:~$
pwd
/home/Sandeep
Sandeep@localhost:~$
cd
../redhat //Change Directory to that
sticky bit directory
Sandeep@localhost:/home/redhat$
ls
mywork
Sandeep@localhost:/home/redhat$
ls
-l
total 4
drwxr-xr-x 3
redhat adm 4096 2013-10-24 15:39 mywork
Sandeep@localhost:/home/redhat$
cd
mywork/
Sandeep@localhost:/home/redhat/mywork$
ls
-l
total 4
drwxr-xr-t 2
redhat adm 4096 2013-10-24 15:36 sticky
Sandeep@localhost:/home/redhat/mywork$
Sandeep@localhost:/home/redhat/mywork$
cd sticky/
Sandeep@localhost:/home/redhat/mywork/sticky$
ls
stickybit.sh stickybit.sh_bak
//Trying to remove sticky bit set directory content
..getting error permission denied
Sandeep@localhost:/home/redhat/mywork/sticky$
rm
stickybit.sh
rm: remove
write-protected regular file `stickybit.sh'? y
rm: cannot remove `stickybit.sh': Permission
denied
Sandeep@localhost:/home/redhat/mywork/sticky$
|
Permission denied while removing the file which resides into
the directory whose sticky bit has been set already. This is the actual use of
sticky bit on directory.
How to remove sticky
bit of directory/file ?
We need to login by redhat or root user before removing
sticky bit then only we can remove the Sticky bit.
redhat@localhost:~/mywork$
ls –l
total 4
drwxr-xr-t 2
redhat adm 4096 2013-10-24 15:36 sticky
//use below syntax or use – chmod 755 sticky
redhat@localhost:~/mywork$
chmod
-t sticky/
redhat@localhost:~/mywork$
ls
-l
total 4
drwxr-xr-x 2
redhat adm 4096 2013-10-24 15:36 sticky
redhat@localhost:~/mywork$
|
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