chmod(1) chmod(1)
NAME
chmod - change file mode
SYNOPSIS
chmod [-R] mode file . . .
chmod [-R][ugoa]{ + | - | = }[rwxXlstugo] file . . .
DESCRIPTION
chmod changes or assigns the mode of a file. The mode of a
file specifies its permissions and other attributes. The mode
may be absolute or symbolic.
An absolute mode is specified using octal numbers:
chmod nnnn file . . .
where n is a number from 0 to 7. An absolute mode is
constructed from the OR of any of the following modes:
4000 Set user ID on execution.
20#0 Set group ID on execution if # is 7, 5, 3, or
1.
Enable mandatory locking if # is 6, 4, 2, or
0.
This bit is ignored if the file is a
directory; it may be set or cleared only using
the symbolic mode.
1000 Turn on sticky bit [see chmod(2)].
0400 Allow read by owner.
0200 Allow write by owner.
0100 Allow execute (search in directory) by owner.
0070 Allow read, write, and execute (search) by
group.
0007 Allow read, write, and execute (search) by
others.
On execution, the setuid and setgid modes affect interpreter
scripts only if the first line of those scripts is
#! pathname [arg]
where pathname is the path of a command interpreter, such as
sh. [See exec(2).]
A symbolic mode is specified in the following format:
chmod [who ] operator [permission(s)] file . . .
who is zero or more of the characters u, g, o, and a
specifying whose permissions are to be changed or assigned:
u user's permissions
g group's permissions
o others' permissions
a all permissions (user, group, and other)
If who is omitted, it defaults to a.
operator is one of +, -, or =, signifying how permissions are
to be changed:
+ Add permissions.
- Take away permissions.
= Assign permissions absolutely.
Unlike other symbolic operations, = has an absolute effect in
that it resets all other bits. Omitting permission(s) is
useful only with = to take away all permissions.
permission(s) is any compatible combination of the following
letters:
r read permission
w write permission
x execute permission
X conditional execute permission (see below)
s user or group set-ID
t sticky bit
l mandatory locking
u, g, o indicate that permission is to be taken from
the current user, group or other mode
respectively. Only one of these options may
be used at a time.
The X represents the execute permission of a file only if the
file is a directory, or if the current (unmodified) file
permissions have at least one execute bit present. If neither
of these conditions are true, it will be ignored.
Permissions to a file may vary depending on your user
identification number (UID) or group identification number
(GID). Permissions are described in three sequences each
having three characters:
User Group Other
rwx rwx rwx
This example (user, group, and others all have permission to
read, write, and execute a given file) demonstrates two
categories for granting permissions: the access class and the
permissions themselves.
Multiple symbolic modes separated by commas may be given,
though no spaces may intervene between these modes.
Operations are performed in the order given. Multiple
symbolic letters following a single operator cause the
corresponding operations to be performed simultaneously.
The letter s is only meaningful when who includes u or g, and
t only works with u.
Mandatory file and record locking (l) refers to a file's
ability to have its reading or writing permissions locked
while a program is accessing that file. When locking is
requested, the group ID of the user must be the same as the
group ID of the file. It is not possible to permit group
execution and enable a file to be locked on execution at the
same time. In addition, it is not possible to turn on the
set-group-ID bit and enable a file to be locked on execution
at the same time. The following examples, therefore, are
invalid and elicit error messages:
chmod g+x,+l file
chmod g+s,+l file
Only the owner of a file or directory (or a privileged user)
may change that file's or directory's mode. Only a privileged
user may set the sticky bit on a non-directory file.
Otherwise, chmod will mask the sticky-bit but will not return
an error. In order to turn on a file's set-group-ID bit, your
own group ID must correspond to the file's and group execution
must be set.
The -R option recursively descends through directory
arguments, setting the mode for each file as described above.
If a symbolic link is encountered whose target is a directory,
the permission of the directory is changed. That directory's
contents are not recursively traversed.
USAGE
Deny execute permission to everyone:
chmod a-x file
Allow read permission to everyone:
chmod 444 file
Make a file readable and writable by the group and others:
chmod go+rw file
chmod 066 file
Cause a file to be locked during access:
chmod +l file
Allow everyone to read, write, and execute the file and turn
on the set group-ID.
chmod =rwx,g+s file
chmod 2777 file
Absolute changes don't work for the set-group-ID bit of a
directory. You must use g+s or g-s.
If the ACL Package is installed, and the file system is of
type sfs or vxfs,, additional access permissions, beyond those
represented by the three sets of permissions in the mode bits,
may also be placed on a file using an Access Control List
(ACL).
Files
/usr/lib/locale/locale/LC_MESSAGES/uxcore.abi
language-specific message file [See LANG on environ(5).]
REFERENCES
chmod(2), getacl(1), ls(1), setacl(1)
NOTICES
chmod permits you to produce useless modes so long as they are
not illegal (for example, making a text file executable).
chmod does not check the file type to see if mandatory locking
is available.
Normally, the effective user and group ID of a process is the
user and group ID of the invoking process. If the set-user-ID
(set-group-ID) on execution mode bit of an executable file is
set, the effective user (group) ID of the process, when the
file is invoked, is the owner (group) ID of the executable
file. The real user ID and real group ID of the new process
remain the same as those of the calling process.
Setting the ``set-group-ID on execution'' bit on a directory
(via the g+s option) means that any files subsequently created
in that directory will automatically be given the group ID of
that directory.
Neither set-user-ID nor set-group-ID mode bits affect shell
script privileges. This is true only if the script does not
begin with #! path.
When symbolic links are created by ln, they are made with
permissions set to read, write, and execute for owner, group,
and world (777). A chmod applied to a symbolic link acts on
the target of the link, not on the link itself.
The symbolic modes should be used in preference to the octal
representation, since the octal representation may not be
supported in future releases.
If who is not specified, POSIX.2 requires use of umask. Use
the POSIX2 environmental variable to get POSIX.2 behavior.
The POSIX.2 behavior is inconsistent with existing System V
behavior.