.\" Copyright (c) 1989, 1990, 1993, 1994
.\" The Regents of the University of California. All rights reserved.
.\" This code is derived from software contributed to Berkeley by
.\" the Institute of Electrical and Electronics Engineers, Inc.
.\" %sccs.include.redist.roff%
.\" @(#)chmod.1 8.3 (Berkeley) %G%
utility modifies the file mode bits of the listed files
The options are as follows:
option is specified, symbolic links on the command line are followed.
(Symbolic links encountered in the tree traversal are not followed.)
option is specified, all symbolic links are followed.
option is specified, no symbolic links are followed.
Change the modes of the file hierarchies rooted in the files
instead of just the files themselves.
Symbolic links do not have modes, so unless the
on a symbolic link is a no-op.
options are ignored unless the
In addition, these options override each other and the
command's actions are determined by the last one specified.
Only the owner of a file or the super-user is permitted to change
utility exits 0 on success, and >0 if an error occurs.
Modes may be absolute or symbolic.
An absolute mode is an octal number constructed by
.Bl -tag -width 6n -compact -offset indent
set-group-ID-on-execution
execute (or search for directories) by owner
read, write, execute/search by group
read, write, execute/search by others
The read, write, and execute/search values for group and others
are encoded as described for owner.
The symbolic mode is described by the following grammar:
.Bd -literal -offset indent
mode ::= clause [, clause ...]
clause ::= [who ...] [action ...] last_action
last_action ::= op [perm ...]
perm ::= r | s | t | w | x | X | u | g | o
symbols ``u'', ``g'', and ``o'' specify the user, group, and other parts
of the mode bits, respectively.
symbol ``a'' is equivalent to ``ugo''.
symbols represent the portions of the mode bits as follows:
.Bl -tag -width Ds -compact -offset indent
The set-user-ID-on-execution and set-group-ID-on-execution bits.
The execute/search bits if the file is a directory or any of the
execute/search bits are set in the original (unmodified) mode.
symbol ``X'' are only meaningful in conjunction with the
symbol ``+'', and are ignored in all other cases.
The user permission bits in the mode of the original file.
The group permission bits in the mode of the original file.
The other permission bits in the mode of the original file.
symbols represent the operation performed, as follows:
If no value is supplied for
the ``+'' operation has no effect.
If no value is supplied for
each permission bit specified in
for which the corresponding bit in the file mode creation mask
Otherwise, the mode bits represented by the specified
If no value is supplied for
the ``\-'' operation has no effect.
If no value is supplied for
each permission bit specified in
for which the corresponding bit in the file mode creation mask
Otherwise, the mode bits represented by the specified
The mode bits specified by the
value are cleared, or, if no who value is specified, the owner, group
and other mode bits are cleared.
Then, if no value is supplied for
each permission bit specified in
for which the corresponding bit in the file mode creation mask
Otherwise, the mode bits represented by the specified
specifies one or more operations to be performed on the mode
bits, and each operation is applied to the mode bits in the
Operations upon the other permissions only (specified by the symbol
``o'' by itself), in combination with the
symbols ``s'' or ``t'', are ignored.
.Bl -tag -width "u=rwx,go=u-w" -compact
make a file readable by anyone and writable by the owner only.
deny write permission to group and others.
set the read and write permissions to the usual defaults, but
retain any execute permissions that are currently set.
make a directory or file searchable/executable by everyone if it is
already searchable/executable by anyone.
make a file readable/executable by everyone and writable by the owner only.
clear all mode bits for group and others.
set the group bits equal to the user bits, but clear the group write bit.
option for the naughty bits.
utility is expected to be POSIX 1003.2
compatible with the exception of the
which are not included in that standard.
projects / unix-history / blob