CHMOD
Section: User Commands (1)
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NAME
chmod
- change file modes
SYNOPSIS
[-R
[-H | -L | -P
]
]
[-h
]
mode
file ...
DESCRIPTION
The
utility modifies the file mode bits of the listed files
as specified by the
mode
operand.
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.
Unless the
-H
or
-L
option is set,
on a symbolic link always succeeds and has no effect.
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.
Only the owner of a file or the super-user is permitted to change
the mode of a file.
The
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.
BUGS
There's no
perm
option for the naughty bits.
SEE ALSO
install(1),
chmod(2),
stat(2),
umask(2),
fts(3),
setmode(3),
symlink(7),
chown(8)
STANDARDS
The
utility is expected to be
St -p1003.2
compatible with the exception of the
perm
symbols
``t''
and
``X''
which are not included in that standard.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- MODES
-
- EXAMPLES
-
- BUGS
-
- SEE ALSO
-
- STANDARDS
-
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