Special Access Modes for Linux/Solaris

# chmod 4755 uid Setuid access # chmod 2755 gid Setgid access # chmod 6755 both Setuid and setgid access: 2 highest bits on # chmod 1777 sticky Sticky bit # chmod 2745 locking File locking (note that group execute is off) # ls -ld -rwsr-sr-x 1 root chem 0 Mar 30 11:37 both -rwxr-sr-x 1 root chem 0 Mar 30 11:37 gid -rwxr-Sr-x 1 root chem 0 Mar 30 11:37 locking drwxrwxrwt 2 root chem 8192 Mar 30 11:39 sticky -rwsr-xr-x 1 root chem 0 Mar 30 11:37 uid 

t - save text mode, sticky bit
Files: Keep executable in memory after exit.Directories: Restrict deletions to each user's own files.

s - setuid bit
Files: Set process user ID on execution.

s - setgid bit
Files: Set process group ID on execution.Directories: New files inherit directory group owner.

l - file locking
Files: Set mandatory file locking on reads/writes (Solaris and Tru64 and sometimes Linux). This mode is set via the group access type and requires that group execute access is off. Displayed as S in ls -l listings.

* From O'Reilly Essentail System Administration - 3rd Edition