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.\" Sccsid @(#)chmod.1	1.15 (gritter) 1/24/05
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.TH CHMOD 1 "1/24/05" "Heirloom Toolchest" "User Commands"
.SH NAME
chmod \- change mode
.SH SYNOPSIS
\fBchmod\fR [\fB\-R\fR] \fImode\fR \fIfile\fR ...
.SH DESCRIPTION
The mode of
each named file
is changed
according to
.I mode,
which may be absolute or symbolic.
An absolute
.I mode
is an octal
number constructed
from the OR of the
following modes:
.TP 10
4000
Set user ID on execution.
.br
.br
.ns
.TP 10
20#0
Set group ID on execution if # is 7, 5, 3, or 1
and
.I file
is not a directory.
.br
Enable mandatory locking if # is 6, 4, 2, or 0
and
.I file
is not a directory.
.br
If
.I file
is a directory,
files created in this directory
will get the group
.SM ID
of the directory
instead of the current process
(may be set or cleared using explicit symbolic modes only).
.br
.br
.ns
.TP 10
1000
Sticky bit.
If file is a directory,
only the owner of the file or the super-user
can rename or delete a file in that directory.
.br
.br
.ns
.TP 10
0400
Read by owner.
.br
.br
.ns
.TP 10
0200
Write by owner.
.br
.br
.ns
.TP 10
0100
Execute (search in directory) by owner.
.br
.br
.ns
.TP 10
0070
Read, write, execute (search) by group.
.br
.br
.ns
.TP 10
0007
Read, write, execute (search) by others.
.PP
A symbolic
.I mode
has the form:
.IP
.RI [ who ]
.I op permission
.RI [ "op permission" "] ..."
.PP
The
.I who
part is a combination
of the letters 
.B u
(for user's permissions),
.B g
(group)
and
.B o
(other).
The letter
.B a
stands for
.B ugo.
If
.I who
is omitted,
the default is
.I a
but the setting of
the file creation mask
(see umask(2))
is taken into account
for
.B /usr/5bin/posix/chmod
and
.BR /usr/5bin/posix2001/chmod.
.PP
.I Op
can be
.B +
to add
.I permission
to the file's mode,
.B \-
to take away
.I permission
and
.B =
to assign
.I permission
absolutely
(all other bits will
be reset).
.PP
.I Permission
is any combination of the letters
.B r
(read),
.B w
(write),
.B x
(execute),
.B X
(execute if file is a directory
or if it already has at least one execute bit set),
.B s
(set owner or group id),
.B t
(save text \- sticky),
and
.B l
(mandatory locking).
Letters
.BR u,
.B g
or
.B o
indicate that
.I permission
is to be taken
from the current
mode.
Omitting
.I permission
is only useful
with
.B =
to take away
all permissions.
.PP
The first example denies write permission to others,
the second makes a file executable:
.IP
chmod o\-w file
.br
chmod +x file
.PP
Multiple symbolic modes separated by commas may be given.
Operations are performed
in the order specified.
The letter
.B s
is only useful
with
.B u
or
.B g.
.PP
Only the owner of a file (or the super-user) may change its mode.
.PP
The
.B chmod
command accepts the following option:
.TP
.B \-R
Recursively descend each
.I file
operand.
If a symbolic link is encountered,
the permissions of its target are changed,
but the link is not followed otherwise.
.SH "SEE ALSO"
chown(1),
ls(1),
chmod(2),
stat(2),
umask(2)
.SH NOTES
Use of the
.B \-R
option is not generally recommended
since symbolic links can lead to modification
of files at arbitrary places outside the file hierarchies
specified as arguments. The
.IR find (1)
command can be used in combination with
.I chmod
to achieve the desired result in a more controlled manner.
For example,
.in +2
.sp
find . ! \-type l \-exec chmod u+w {} +
.sp
.in -2
will add write permission for the invoking user,
and
.in +2
.sp
find . \-type d \-exec chmod a+rx {} + \-o \e
        ! \-type l ! \-type d \-exec chmod a+r {} +
.sp
.in -2
will make the file hierarchy accessible to all users.