CHMOD(1) CHMOD(1)
NAME
chmod - change mode
SYNOPSIS
chmod mode file ...
chmod mode directory ...
DESCRIPTION
The permissions of the named files or directories are
changed according to mode, which may be symbolic or
absolute. Absolute changes to permissions are stated using
octal numbers:
chmod nnn file(s)
where n is a number from 0 to 7. Symbolic changes are
stated using mnemonic characters:
chmod a operator b file(s)
where a is one or more characters corresponding to user,
group, or other; where operator is +, -, and =, signifying
assignment of permissions; and where b is one or more
characters corresponding to type of permission.
An absolute mode is given as an octal number constructed
from the OR 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
1000 sticky bit is turned on ((see chmod(2))
0400 read by owner
0200 write by owner
0100 execute (search in directory) by owner
0070 read, write, execute (search) by group
0007 read, write, execute (search) by others
Symbolic changes are stated using letters that correspond
both to access classes and to the individual permissions
themselves. 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 (meaning that user, group, and others all have
reading, writing, and execution permission to a given file)
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CHMOD(1) CHMOD(1)
demonstrates two categories for granting permissions: the
access class and the permissions themselves.
Thus, to change the mode of a file's (or directory's)
permissions using chmod's symbolic method, use the following
syntax for mode:
[ who ] operator [ permission(s) ], ...
A command line using the symbolic method would appear as
follows:
chmod g+rw file
This command would make file readable and writable by the
group.
The who part can be stated as one or more of the following
letters:
u user's permissions
g group's permissions
o others permissions
The letter a (all) is equivalent to ugo and is the default
if who is omitted.
Operator can be + to add permission to the file's mode, - to
take away permission, or = to assign permission absolutely.
(Unlike other symbolic operations, = has an absolute effect
in that it resets all other bits.) Omitting permission is
only useful with = to take away all permissions.
Permission is any compatible combination of the following
letters:
r reading permission
w writing permission
x execution permission
s user or group set-ID is turned on
t sticky bit is turned on
l mandatory locking will occur during access
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. It is not possible
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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 and enable a file to be locked
on execution at the same time. The following examples,
chmod g+x,+l file
chmod g+s,+l file
are, therefore, illegal usages and will elicit error
messages.
Only the owner of a file or directory (or the super-user)
may change a file's mode. Only the super-user may set the
sticky bit. In order to turn on a file's set-group-ID, your
own group ID must correspond to the file's, and group
execution must be set.
EXAMPLES
chmod a-x file
chmod 444 file
The first examples deny execution permission to all. The
absolute (octal) example permits only reading permissions.
chmod go+rw file
chmod 606 file
These examples make a file readable and writable by the
group and others.
chmod +l file
This causes a file to be locked during access.
chmod =rwx,g+s file
chmod 2777 file
These last two examples enable all to read, write, and
execute the file; and they turn on the set group-ID.
NOTES
In a Remote File Sharing environment, you may not have the
permissions that the output of the ls -l command leads you
to believe. For more information see the "Mapping Remote
Users" section of Chapter 10 of the System Administrator's
Guide.
SEE ALSO
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CHMOD(1) CHMOD(1)
ls(1).
chmod(2) in the Programmer's Reference Manual.
ORIGIN
AT&T V.3
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