xref: /freebsd/bin/chmod/chmod.1 (revision 90aea514c6249118e880d75972d063362f4bf492)

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.Dd January 7, 2017
.Dt CHMOD 1
.Os
.Sh NAME
.Nm chmod
.Nd change file modes
.Sh SYNOPSIS
.Nm
.Op Fl fhv
.Op Fl R Op Fl H | L | P
.Ar mode
.Ar
.Sh DESCRIPTION
The
.Nm
utility modifies the file mode bits of the listed files
as specified by the
.Ar mode
operand.
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl f
Do not display a diagnostic message if
.Nm
could not modify the mode for
.Va file ,
nor modify the exit status to reflect such failures.
.It Fl H
If the
.Fl R
option is specified, symbolic links on the command line are followed
and hence unaffected by the command.
(Symbolic links encountered during tree traversal are not followed.)
.It Fl h
If the file is a symbolic link, change the mode of the link itself
rather than the file that the link points to.
.It Fl L
If the
.Fl R
option is specified, all symbolic links are followed.
.It Fl P
If the
.Fl R
option is specified, no symbolic links are followed.
This is the default.
.It Fl R
Change the modes of the file hierarchies rooted in the files,
instead of just the files themselves.
Beware of unintentionally matching the
.Dq Pa ".."
hard link to the parent directory when using wildcards like
.Dq Li ".*" .
.It Fl v
Cause
.Nm
to be verbose, showing filenames as the mode is modified.
If the
.Fl 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.
.El
.Pp
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
If
.Nm
receives a
.Dv SIGINFO
signal (see the
.Cm status
argument for
.Xr stty 1 ) ,
then the current filename as well as the old and new modes are displayed.
.Pp
Only the owner of a file or the super-user is permitted to change
the mode of a file.
.Sh EXIT STATUS
.Ex -std
.Sh 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:
.Pp
.Bl -tag -width 6n -compact -offset indent
.It Li 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
.Xr chmod 2
and the
.Cm suiddir
option to
.Xr mount 8 .
.It Li 2000
(the setgid bit).
Executable files with this bit set
will run with effective gid set to the gid of the file owner.
.It Li 1000
(the sticky bit).
See
.Xr chmod 2
and
.Xr sticky 7 .
.It Li 0400
Allow read by owner.
.It Li 0200
Allow write by owner.
.It Li 0100
For files, allow execution by owner.
For directories, allow the owner to
search in the directory.
.It Li 0040
Allow read by group members.
.It Li 0020
Allow write by group members.
.It Li 0010
For files, allow execution by group members.
For directories, allow
group members to search in the directory.
.It Li 0004
Allow read by others.
.It Li 0002
Allow write by others.
.It Li 0001
For files, allow execution by others.
For directories allow others to
search in the directory.
.El
.Pp
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).
.Pp
The symbolic mode is described by the following grammar:
.Bd -literal -offset indent
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
.Ed
.Pp
The
.Ar who
symbols ``u'', ``g'', and ``o'' specify the user, group, and other parts
of the mode bits, respectively.
The
.Ar who
symbol ``a'' is equivalent to ``ugo''.
.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-on-execution 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 ``X'' are only meaningful in conjunction with the
.Ar op
symbol ``+'', and are ignored in all other cases.
.It u
The user permission bits in the original mode of the file.
.It g
The group permission bits in the original mode of the file.
.It o
The other permission bits in the original mode of the file.
.El
.Pp
The
.Ar op
symbols represent the operation performed, as follows:
.Bl -tag -width 4n
.It +
If no value is supplied for
.Ar perm ,
the ``+'' 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
(see
.Xr umask 2 )
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 ``\-'' 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 set, 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 owner, 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
``o'' by itself), in combination with the
.Ar perm
symbols ``s'' or ``t'', are ignored.
.Pp
The ``w'' permission on directories will permit file creation, relocation,
and copy into that directory.
Files created within the directory itself will inherit its group ID.
.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 COMPATIBILITY
The
.Fl v
option is non-standard and its use in scripts is not recommended.
.Sh SEE ALSO
.Xr chflags 1 ,
.Xr install 1 ,
.Xr setfacl 1 ,
.Xr chmod 2 ,
.Xr stat 2 ,
.Xr umask 2 ,
.Xr fts 3 ,
.Xr setmode 3 ,
.Xr sticky 7 ,
.Xr symlink 7 ,
.Xr chown 8 ,
.Xr mount 8
.Sh STANDARDS
The
.Nm
utility is expected to be
.St -p1003.2
compatible with the exception of the
.Ar perm
symbol
.Dq t
which is not included in that standard.
.Sh HISTORY
A
.Nm
command appeared in
.At v1 .
.Sh BUGS
There is no
.Ar perm
option for the naughty bits of a horse.