The
utility modifies the file mode bits of the listed files
as specified by the
mode
operand.
The options are as follows:
-f
Do not display a diagnostic message if
could not modify the mode for
file
nor modify the exit status to reflect such failures.
-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 by
default.)
-h
If the file is a symbolic link, change the mode of the link itself
rather than the file that the link points to.
-L
If the
-R
option is specified, all symbolic links are followed.
-P
If the
-R
option is specified, no symbolic links are followed.
This is the default.
-R
Change the modes of the file hierarchies rooted in the files
instead of just the files themselves.
-v
Cause
to be verbose, showing filenames as the mode is modified.
If the
-v
flag is specified more than once, the old and new modes of the file
will also be printed, in both octal and symbolic notation.
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.
EXIT STATUS
Ex -std
MODES
Modes may be absolute or symbolic.
An absolute mode is an octal number constructed from the sum of
one or more of the following values:
4000
(the setuid bit).
Executable files with this bit set
will run with effective uid set to the uid of the file owner.
Directories with this bit set will force all files and
sub-directories created in them to be owned by the directory owner
and not by the uid of the creating process, if the underlying file
system supports this feature: see
chmod(2)
and the
suiddir
option to
mount(8).
2000
(the setgid bit).
Executable files with this bit set
will run with effective gid set to the gid of the file owner.
For files, allow execution by owner.
For directories, allow the owner to
search in the directory.
0040
Allow read by group members.
0020
Allow write by group members.
0010
For files, allow execution by group members.
For directories, allow
group members to search in the directory.
0004
Allow read by others.
0002
Allow write by others.
0001
For files, allow execution by others.
For directories allow others to
search in the directory.
For example, the absolute mode that permits read, write and execute by
the owner, read and execute by group members, read and execute by
others, and no set-uid or set-gid behaviour is 755
(400+200+100+040+010+004+001).
The symbolic mode is described by the following grammar:
mode ::= clause [, clause ...]
clause ::= [who ...] [action ...] action
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 original mode of the file.
g
The group permission bits in the original mode of the file.
o
The other permission bits in the original mode of the 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
(see
umask(2))
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.
COMPATIBILITY
The
-v
option is non-standard and its use in scripts is not recommended.
