Tell me the sticky bit operation?

SUID

The sticky bit applied to executable programs flagging the system to keep an image of the program in memory after the program finished running.

But i don't know what's stored in memory And how i can see them, in this case. ?

This is probably one of my most irksome things that people mess up all the time The suidguid bit and the sticky bit are two entirely different things

If you do a man chmod you can read about the SUID and sticky-bits. The man page is available here as well.

background

excerpt

The letters rwxXst select file mode bits for the affected users: read (r), write (w), execute (or search for directories) (x), execute/search only if the file is a directory or already has execute permission for some user (X), set user or group ID on execution (s), restricted deletion flag or sticky bit (t).

SUID/GUID

What the above man page is trying to say is that the position that the x bit takes in the rwxrwxrwx for the user octal (1st group of rwx) and the group octal (2nd group of rwx) can take an additional state where the x becomes an s. When this occurs this file when executed (if it's a program and not just a shell script) will run with the permissions of the owner or the group of the file.

So if the file is owned by root and the suid bit is turned on, the program will run as root. Even if you're running it as a regular user The same thing applies to the guid bit

excerpt

SETUID AND SETGID BITS

chmod clears the set-group-ID bit of a regular file if the file's group ID does not match the user's effective group ID or one of the user's supplementary group IDs, unless the user has appropriate privileges. Additional restrictions may cause the set-user-ID and set-group-ID bits of MODE or RFILE to be ignored. This behavior depends on the policy and functionality of the underlying chmod system call. When in doubt, check the underlying system behavior.

chmod preserves a directory's set-user-ID and set-group-ID bits unless you explicitly specify otherwise. You can set or clear the bits with symbolic modes like u+s and g-s, and you can set (but not clear) the bits with a numeric mode.

SUID/GUID examples

no suid/guid - just the bits rwxr-xr-x are set.

$ ls -lt b.pl
-rwxr-xr-x 1 root root 179 Jan  9 01:01 b.pl

suid & user's executable bit enabled (lowercase s) - the bits rwsr-x-r-x are set.

$ chmod u+s b.pl
$ ls -lt b.pl
-rwsr-xr-x 1 root root 179 Jan  9 01:01 b.pl

suid enabled & executable bit disabled (uppercase S) - the bits rwSr-xr-x are set.

$ chmod u-x b.pl
$ ls -lt b.pl
-rwSr-xr-x 1 root root 179 Jan  9 01:01 b.pl

guid & group's executable bit enabled (lowercase s) - the bits rwxr-sr-x are set.

$ chmod g+s b.pl
$  ls -lt b.pl
-rwxr-sr-x 1 root root 179 Jan  9 01:01 b.pl

guid enabled & executable bit disabled (uppercase S) - the bits rwxr-Sr-x are set.

$ chmod g-x b.pl
$  ls -lt b.pl
-rwxr-Sr-x 1 root root 179 Jan  9 01:01 b.pl

sticky bit

The sticky bit on the other hand is denoted as t , such as with the /tmp directory.

$ ls -l /|grep tmp
drwxrwxrwt. 168 root root 28672 Jun 14 08:36 tmp

This bit should have always been called the restricted deletion bit since that's what it really means When this mode bit is enabled it renders a directory so that users can only delete directories within it that belong to the owner

excerpt

RESTRICTED DELETION FLAG OR STICKY BIT

The restricted deletion flag or sticky bit is a single bit, whose interpretation depends on the file type. For directories, it
prevents unprivileged users from removing or renaming a file in the directory unless they own the file or the directory; this is called the restricted deletion flag for the directory, and is commonly found on world-writable directories like /tmp. For regular files on some older systems, the bit saves the program's text image on the swap device so it will load more quickly when run; this is called the sticky bit.