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CHMOD(1) General Commands Manual CHMOD(1)
NAME
chmod - change file modes
SYNOPSIS
chmod [-R [-H | -L | -P]] [-dfh] mode file ...
chmod [-R [-H | -L | -P]] [-dfh] --reference=rfile file ...
DESCRIPTION
The chmod utility modifies the file mode bits of the listed files as
specified by the mode operand, or copied from a reference rfile, as
specified with the --reference argument.
The options are as follows:
-H If the -R option is specified, symbolic links on the command line
are followed. (Symbolic links encountered in the tree traversal
are not followed.)
-L If the -R option is specified, all symbolic links are followed.
-P If the -R option is specified, no symbolic links are followed.
-R Change the modes of the file hierarchies rooted in the files
instead of just the files themselves.
-d Do not attempt to change the mode of a file if its mode is
already as requested.
-f Do not display a diagnostic message or modify the exit status if
chmod fails to change the mode of a file.
-h If file is symbolic link, the mode of the link is changed.
The -H, -L and -P options are ignored unless the -R option is specified.
In addition, these options override each other and the command's actions
are determined by the last one specified. The default is as if the -P
option had been specified.
Only the owner of a file or the super-user is permitted to change the
mode of a file.
EXIT STATUS
The chmod utility exits 0 on success, and >0 if an error occurs.
MODES
Modes may be absolute or symbolic. An absolute mode is an octal number
constructed by or'ing the following values:
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 (or search for directories) by owner
0070 read, write, execute/search by group
0007 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:
mode ::= clause [, clause ...]
clause ::= [who ...] [action ...] last_action
action ::= op [perm ...]
last_action ::= op [perm ...]
who ::= a | u | g | o
op ::= + | - | =
perm ::= r | s | t | w | x | X | u | g | o
The who symbols ``u'', ``g'', and ``o'' specify the user, group, and
other parts of the mode bits, respectively. The who symbol ``a'' is
equivalent to ``ugo''.
The perm symbols represent the portions of the mode bits as follows:
r The read bits.
s The set-user-ID-on-execution and set-group-ID-on-execution
bits.
t The sticky bit.
w The write bits.
x The execute/search bits.
X The execute/search bits if the file is a directory or any
of the execute/search bits are set in the original
(unmodified) mode. Operations with the perm symbol ``X''
are only meaningful in conjunction with the op symbol
``+'', and are ignored in all other cases.
u The user permission bits in the mode of the original file.
g The group permission bits in the mode of the original file.
o The other permission bits in the mode of the original file.
The op symbols represent the operation performed, as follows:
+ If no value is supplied for perm, the ``+'' operation has no
effect. If no value is supplied for who, each permission bit
specified in perm, for which the corresponding bit in the file mode
creation mask is clear, is set. Otherwise, the mode bits
represented by the specified who and perm values are set.
- If no value is supplied for perm, the ``-'' operation has no
effect. If no value is supplied for who, each permission bit
specified in perm, for which the corresponding bit in the file mode
creation mask is clear, is cleared. Otherwise, the mode bits
represented by the specified who and perm values are cleared.
= The mode bits specified by the who 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 who, each permission
bit specified in perm, for which the corresponding bit in the file
mode creation mask is clear, is set. Otherwise, the mode bits
represented by the specified who and perm values are set.
Each clause specifies one or more operations to be performed on the mode
bits, and each operation is applied to the mode bits in the order
specified.
Operations upon the other permissions only (specified by the symbol ``o''
by itself), in combination with the perm symbols ``s'' or ``t'', are
ignored.
EXAMPLES
644 make a file readable by anyone and writable by the owner
only.
go-w deny write permission to group and others.
=rw,+X set the read and write permissions to the usual defaults,
but retain any execute permissions that are currently set.
+X make a directory or file searchable/executable by everyone
if it is already searchable/executable by anyone.
755
u=rwx,go=rx
u=rwx,go=u-w make a file readable/executable by everyone and writable by
the owner only.
go= clear all mode bits for group and others.
g=u-w set the group bits equal to the user bits, but clear the
group write bit.
SEE ALSO
chflags(1), install(1), chmod(2), stat(2), umask(2), fts(3), setmode(3),
symlink(7), chown(8)
STANDARDS
The chmod utility is expected to be IEEE Std 1003.2-1992 ("POSIX.2")
compatible with the exception of the perm symbol "t" which is not
included in that standard.
HISTORY
A chmod utility appeared in Version 1 AT&T UNIX.
BUGS
There's no perm option for the naughty bits.
NetBSD 10.99 August 11, 2016 NetBSD 10.99