chmod - change mode
chmod mode file ...
The mode of each named file is changed according to mode, which may be absolute or sym-
bolic. An absolute mode is an octal number constructed from the OR of the following
4000 set user ID on execution
2000 set group ID on execution
1000 sticky bit, see chmod(2)
0400 read by owner
0200 write by owner
0100 execute (search in directory) by owner
0070 read, write, execute (search) by group
0007 read, write, execute (search) by others
A symbolic mode has the form:
[who] op permission [op permission] ...
The who part is a combination of the letters u (for user's permissions), g (group) and o
(other). The letter a stands for ugo. If who is omitted, the default is a but the set-
ting of the file creation mask (see umask(2)) is taken into account.
Op can be + to add permission to the file's mode, - to take away permission and = to
assign permission absolutely (all other bits will be reset).
Permission is any combination of the letters r (read), w (write), x (execute), s (set
owner or group id) and t (save text - sticky). Letters u, g or o indicate that permission
is to be taken from the current mode. Omitting permission is only useful with = to take
away all permissions.
The first example denies write permission to others, the second makes a file executable:
chmod o-w file
chmod +x file
Multiple symbolic modes separated by commas may be given. Operations are performed in the
order specified. The letter s is only useful with u or g.
Only the owner of a file (or the super-user) may change its mode.
ls(1), chmod(2), chown (1), stat(2), umask(2)