bin/chmod/chmod.1

.\"	$OpenBSD: chmod.1,v 1.41 2015/12/31 23:38:16 guenther Exp $
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.\"	@(#)chmod.1	8.4 (Berkeley) 3/31/94
.\"
.Dd $Mdocdate: December 31 2015 $
.Dt CHMOD 1
.Os
.Sh NAME
.Nm chmod
.Nd change file modes
.Sh SYNOPSIS
.Nm chmod
.Op Fl h
.Oo
.Fl R
.Op Fl H | L | P
.Oc
.Ar mode
.Ar
.Sh DESCRIPTION
The
.Nm
utility modifies the file mode bits of the listed files
as specified by the
.Ar mode
operand.
The mode of a file dictates its permissions, among other attributes.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl H
If the
.Fl R
option is also specified, symbolic links on the command line are followed.
Symbolic links encountered in the tree traversal are not followed.
.It Fl h
Treat symbolic links like other files: modify links instead of
following them.
The
.Fl h
and
.Fl R
options are mutually exclusive.
.It Fl L
If the
.Fl R
option is also specified, all symbolic links are followed.
.It Fl P
If the
.Fl R
option is also specified, no symbolic links are followed.
.It Fl R
Recurse.
Where
.Ar file
is a directory,
change the mode of the directory and all the files and directories
in the file hierarchy below it.
.El
.Pp
Symbolic links have modes,
but those modes have no effect on the kernel's access checks.
The
.Fl H ,
.Fl L ,
and
.Fl P
options are ignored unless the
.Fl R
option is specified;
if none of them are given,
the default is to not follow symbolic links.
In addition, these options override each other and the
command's actions are determined by the last one specified.
.Pp
Only the file's owner or the superuser is permitted to change
the mode of a file.
.Ss Absolute modes
Absolute modes are specified according to the following format:
.Bd -filled -offset indent
.Nm chmod
.Ar nnnn
.Ar
.Ed
.Pp
An absolute mode is an octal number (specified as
.Ar nnnn ,
where
.Ar n
is a number from 0 to 7) constructed by ORing
any of the following values:
.Pp
.Bl -tag -width 6n -compact -offset indent
.It Li 0400
Allow read by owner.
.It Li 0200
Allow write by owner.
.It Li 0100
Allow execution (or search in directories) by owner.
.It Li 0700
Allow read, write, and execute/search by owner.
.It Li 0040
Allow read by group.
.It Li 0020
Allow write by group.
.It Li 0010
Allow execution (or search in directories) by group.
.It Li 0070
Allow read, write, and execute/search by group.
.It Li 0004
Allow read by others.
.It Li 0002
Allow write by others.
.It Li 0001
Allow execution (or search in directories) by others.
.It Li 0007
Allow read, write, and execute/search by others.
.El
.Pp
In addition to the file permission modes, the following mode bits are
available:
.Pp
.Bl -tag -width 6n -compact -offset indent
.It Li 4000
Set-user-ID on execution.
.It Li 2000
Set-group-ID on execution.
.It Li 1000
Enable sticky bit; see
.Xr sticky 8
and
.Xr chmod 2 .
.El
.Pp
The execute bit for a directory is often referred to as the
.Dq search
bit.
In order to access a file, a user must have execute permission in each
directory leading up to it in the filesystem hierarchy.
For example, to access the file
.Pa /bin/ls ,
execute permission is needed on
.Pa / ,
.Pa /bin ,
and, of course, the
.Pa ls
binary itself.
.Ss Symbolic modes
Symbolic modes are specified according to the following format:
.Bd -filled -offset indent
.Nm chmod
.Sm off
.Op Ar who
.Ar op
.Oo Ar perm Oc , Ar ...
.Sm on
.Ar
.Ed
.Pp
The
.Ar who
symbols indicate whose permissions are to be changed or assigned:
.Pp
.Bl -tag -width 4n -compact -offset indent
.It u
User (owner) permissions.
.It g
Group permissions.
.It o
Others permissions.
.It a
All of the above.
.El
.Pp
Do not confuse the
.Sq o
symbol with
.Dq owner .
It is the user bit,
.Sq u ,
that refers to the owner of the file.
.Pp
The
.Ar op
symbols represent the operation performed, as follows:
.Bl -tag -width 4n -offset indent
.It +
If no value is supplied for
.Ar perm ,
the
.Sq +
operation has no effect.
If no value is supplied for
.Ar who ,
each permission bit specified in
.Ar perm ,
for which the corresponding bit in the file mode creation mask
is clear, is set.
Otherwise, the mode bits represented by the specified
.Ar who
and
.Ar perm
values are set.
.It \&\-
If no value is supplied for
.Ar perm ,
the
.Sq \-
operation has no effect.
If no value is supplied for
.Ar who ,
each permission bit specified in
.Ar perm ,
for which the corresponding bit in the file mode creation mask
is clear, is cleared.
Otherwise, the mode bits represented by the specified
.Ar who
and
.Ar perm
values are cleared.
.It =
The mode bits specified by the
.Ar who
value are cleared or, if no
.Ar who
value is specified, the user, group
and other mode bits are cleared.
Then, if no value is supplied for
.Ar who ,
each permission bit specified in
.Ar perm ,
for which the corresponding bit in the file mode creation mask
is clear, is set.
Otherwise, the mode bits represented by the specified
.Ar who
and
.Ar perm
values are set.
.El
.Pp
The
.Ar perm
(permission symbols) represent the portions of the mode bits as follows:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It r
Read bits.
.It s
Set-user-ID and set-group-ID on execution bits.
.It t
Sticky bit.
.It w
Write bits.
.It x
Execute/search bits.
.It 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
.Ar perm
symbol
.Sq X
are only meaningful in conjunction with the
.Ar op
symbol
.Sq + ,
and are ignored in all other cases.
.It u
User permission bits in the mode of the original file.
.It g
Group permission bits in the mode of the original file.
.It o
Other permission bits in the mode of the original file.
.El
.Pp
Each clause (given in a comma-delimited list on the command line) specifies
one or more operations to be performed on the mode bits, and each operation is
applied in the order specified.
.Pp
Operations upon the
.Dq other
permissions (specified by the symbol
.Sq o
by itself), in combination with the
.Ar perm
symbols
.Sq s
or
.Sq t ,
are ignored.
.Sh EXIT STATUS
.Ex -std chmod
.Sh EXAMPLES
Set file readable by anyone and writable by the owner only:
.Pp
.Dl $ chmod 644 file
.Pp
Deny write permission to group and others:
.Pp
.Dl $ chmod go-w file
.Pp
Set the read and write permissions to the usual defaults, but
retain any execute permissions that are currently set:
.Pp
.Dl $ chmod =rw,+X file
.Pp
Make a directory or file searchable/executable by everyone if it is
already searchable/executable by anyone:
.Pp
.Dl $ chmod +X file
.Pp
Any of these commands will make a file readable/executable by everyone and
writable by the owner only:
.Bd -literal -offset indent
$ chmod 755 file
$ chmod u=rwx,go=rx file
$ chmod u=rwx,go=u-w file
.Ed
.Pp
Clear all mode bits for group and others:
.Pp
.Dl $ chmod go= file
.Pp
Set the group bits equal to the user bits, but clear the group write bit:
.Pp
.Dl $ chmod g=u-w file
.Sh SEE ALSO
.Xr chflags 1 ,
.Xr chgrp 1 ,
.Xr find 1 ,
.Xr install 1 ,
.Xr chmod 2 ,
.Xr stat 2 ,
.Xr umask 2 ,
.Xr fts 3 ,
.Xr setmode 3 ,
.Xr symlink 7 ,
.Xr chown 8 ,
.Xr sticky 8
.Sh STANDARDS
The
.Nm
utility is compliant with the
.St -p1003.1-2008
specification.
.Pp
The flags
.Op Fl HLP
are extensions to that specification.
.Pp
The
.Sq t
perm symbol (sticky bit) is marked by
.St -p1003.1-2008
as being an
X/Open System Interfaces
option.
.Sh HISTORY
A
.Nm
command appeared in
.At v1 .
.Sh BUGS
There's no
.Ar perm
option for the naughty bits.