chmod(1) UNIX System V(Essential Utilities) chmod(1)
NAME
chmod - change file mode
SYNOPSIS
chmod [-R] mode file . . .
chmod [ugoa ]{+ |- |=}[ rwxlstugo ] 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.
Upon 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.
10/89 Page 1
chmod(1) UNIX System V(Essential Utilities) chmod(1)
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
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.
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 with 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
Page 2 10/89
chmod(1) UNIX System V(Essential Utilities) chmod(1)
Only the owner of a file or directory (or the super-user) may change that
file's or directory's mode. Only the super-user may set the sticky bit
on a non-directory file. If you are not super-user, 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.
EXAMPLES
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.
SEE ALSO
ls(1).
chmod(2) in the Programmer's Reference Manual
NOTES
chmod permits you to produce useless modes so long as they are not
illegal (e.g., making a text file executable). chmod does not check the
file type to see if mandatory locking is available.
10/89 Page 3