path: root/bin/chmod/chmod.1

.\"	$OpenBSD: chmod.1,v 1.13 1999/07/04 18:59:38 aaron Exp $
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.\"
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.\"	@(#)chmod.1	8.4 (Berkeley) 3/31/94
.\"
.Dd March 31, 1994
.Dt CHMOD 1
.Os
.Sh NAME
.Nm chmod
.Nd change file modes
.Sh SYNOPSIS
.Nm chmod
.Oo
.Fl R
.Op Fl H | Fl L | Fl P
.Oc
.Ar mode
.Op 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 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
Change the modes of the file hierarchies rooted in the files
instead of just the files themselves.
.El
.Pp
Symbolic links do not have modes, so unless the
.Fl H
or
.Fl L
option is set,
.Nm
on a symbolic link always succeeds and has no effect.
The
.Fl H ,
.Fl L
and
.Fl P
options are ignored unless the
.Fl R
option is specified.
In addition, these options override each other and the
command's actions are determined by the last one specified.
.Pp
Only the owner of a file or the super-user is permitted to change
the mode of a file.
.Pp
The
.Nm
utility exits 0 on success or >0 if an error occurred.
.Sh MODES
Modes may be absolute or symbolic.
An absolute mode is an octal number constructed by ORing
the following values:
.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
sticky bit, see
.Xr sticky 8
and
.Xr chmod 2
.It Li 0400
read by owner
.It Li 0200
write by owner
.It Li 0100
execute (or search in directories) by owner
.It Li 0070
read, write, execute/search by group
.It Li 0007
read, write, execute/search by others
.El
.Pp
The read, write, and execute/search values for group and others
are encoded as described for owner. 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.
.Pp
The symbolic mode is described by the following grammar:
.Bd -literal -offset indent
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
.Ed
.Pp
The
.Ar who
symbols
.Sq u ,
.Sq g ,
and
.Sq o
specify the user, group, and other parts
of the mode bits, respectively. The
.Ar who
symbol
.Sq a
is equivalent to
.Sq ugo .
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 perm
symbols represent the portions of the mode bits as follows:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It r
The read bits.
.It s
The set-user-ID- and set-group-ID-on-execution bits.
.It t
The sticky bit.
.It w
The write bits.
.It x
The 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
The user permission bits in the mode of the original file.
.It g
The group permission bits in the mode of the original file.
.It o
The other permission bits in the mode of the original file.
.El
.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
Each
.Ar 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.
.Pp
Operations upon the other permissions only (specified by the symbol
.Sq o
by itself), in combination with the
.Ar perm
symbols
.Sq s
or
.Sq t ,
are ignored.
.Pp
Care must be taken when granting elevated privileges to a program through the
set-user-ID (suid) and set-group-ID (sgid) bits. Do not apply
.Sq s
bits to executables you do not trust. Indeed, the source code which makes up
the suid/sgid binaries shipped with
.Bx Open
has been heavily audited by talented developers. Beware of suid/sgid binaries
from third-party sources and practice safe programming.
.Sh EXAMPLES
.Bl -tag -width "u=rwx,go=u-w" -compact
.It Li 644
Make a file readable by anyone and writable by the owner only.
.Pp
.It Li go-w
Deny write permission to group and others.
.Pp
.It Li =rw,+X
Set the read and write permissions to the usual defaults, but
retain any execute permissions that are currently set.
.Pp
.It Li +X
Make a directory or file searchable/executable by everyone if it is
already searchable/executable by anyone.
.Pp
.It Li 755
.It Li u=rwx,go=rx
.It Li u=rwx,go=u-w
Make a file readable/executable by everyone and writable by the owner only.
.Pp
.It Li go=
Clear all mode bits for group and others.
.Pp
.It Li g=u-w
Set the group bits equal to the user bits, but clear the group write bit.
.El
.Sh SEE ALSO
.Xr chgrp 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 expected to be
.St -p1003.2
compatible with the exception of the
.Ar perm
symbols
.Sq t
and
.Sq X
which are not included in that standard.
.Sh BUGS
There's no
.Ar perm
option for the naughty bits.