V10/man/man1/chmod.1

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.TH CHMOD 1 
.CT 1 files dirs secur
.SH NAME
chmod \- change mode
.SH SYNOPSIS
.B chmod
.I mode file ...
.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.
(Modes that contain a 1000 bit are incompatible with
other modes that have any bits among 7000.)
.TP
4000
set user ID on execution
.PD0
.TP
3000
set exclusive access mode (1 writer or
.I n
readers)
.TP
2000
set group ID on execution
.TP
1000
set synchronized access mode (1 writer and
.I n
readers)
.TP
0400
read by owner
.TP
0200
write by owner
.TP
0100
execute (search in directory) by owner
.TP
0070
read, write, execute (search) by group
.TP
0007
read, write, execute (search) by others
.PD
.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
.BR a .
.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 s
(set owner or group id)
.B e
(set exclusive access mode)
and
.B y
(set synchronized access mode).
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
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
Synchronized access
guards against inconsistent updates
by preventing concurrent opens for writing.
Exclusive access
guards against inconsistent views
by preventing concurrent opens if one is for writing.
.SH EXAMPLES
.TP
.L
chmod o-w file
Deny write permission to others.
.TP
.L
chmod +x file
Make file executable.
.SH "SEE ALSO"
.IR ls (1),
.IR chmod (2),
.IR stat (2),
.IR chdate (1),
.IR chown (8)