CHMOD(1) CHMOD(1)
NAME
chmod - change mode
SYNOPSIS
chmod mode file ...
DESCRIPTION
The mode of each named file is changed according to mode,
which may be absolute or symbolic. An absolute mode is an
octal number constructed from the OR of the following modes.
(Modes that contain a 1000 bit are incompatible with other
modes that have any bits among 7000.)
4000 set user ID on execution
3000 set exclusive access mode (1 writer or n readers)
2000 set group ID on execution
1000 set synchronized access mode (1 writer and n readers)
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.
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) e (set
exclusive access mode) and y (set synchronized access mode).
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.
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.
Synchronized access guards against inconsistent updates by
CHMOD(1) CHMOD(1)
preventing concurrent opens for writing. Exclusive access
guards against inconsistent views by preventing concurrent
opens if one is for writing.
EXAMPLES
chmod o-w file
Deny write permission to others.
chmod +x file
Make file executable.
SEE ALSO
ls(1), chmod(2), stat(2), chdate(1), chown(8)