CHMOD(C) XENIX System V CHMOD(C)
Name
chmod - Changes the access permissions of a file or
directory.
Syntax
chmod mode file ...
chmod [ who ] +-= [ permission ... ] file ...
Description
The chmod command changes the access permissions (or mode)
of a specified file or directory. It is used to control file
and directory access by users other than the owner and
super-user. The mode may be an expression composed of
letters and operators (called symbolic mode), or a number
(called absolute mode).
A chmod command using symbolic mode has the form:
chmod [who] +-= [permission ...] filename
In place of who you can use one or any combination of the
following letters:
a Stands for ``all users''. If who is not indicated on
the command line, a is the default. The definition of
``all users'' depends on the user's umask. See
umask(C).
g Stands for ``group'', all users who have the same group
ID as the owner of the file or directory.
o Stands for ``others'', all users on the system.
u Stands for ``user'', the owner of the file or
directory.
The operators are:
+ Adds permission
- Removes permission
= Assigns the indicated permission and removes all other
permissions (if any) for that who. If no permission is
assigned, existing permissions are removed.
Permissions can be any combination of the following letters:
x Execute (search permission for directories)
r Read
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CHMOD(C) XENIX System V CHMOD(C)
w Write
s Sets owner or group ID on execution of the file to that
of the owner of the file. The mode ``u+s'' sets the
user ID bit for the file. The mode ``g+s'' sets the
group ID bit. Other combinations have no effect.
t Saves text in memory upon execution. (``Sticky bit'',
see chmod(S)). Only the mode ``u+t'' sets the sticky
bit. All other combinations have no effect. This mode
can only be set by the super-user.
l Advisory locking calls on the file will automatically
be promoted to mandatory locking. Applies only to
normal files (not directories, special devcie files,
etc.).
Mandatory file and record locking refers to locking the read
or write permissions while a program is accessing that file.
Under advisory locking, processes are expected to cooperate
by not reading or writing sections of a file unless a lock
can be obtained. The system will not prevent processes from
violating these cooperative procedures as it does with
mandatory locking. A file cannot have group execution
permission and be able to be locked on execution. 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 show illegal uses of chmod and will
generate error messages:
chmod g+x,+l filename
chmod g+s,+l filename
A chmod command using absolute mode has the form:
chmod mode filename
where mode is an octal number constructed by performing
logical OR on the following:
4000 Set user ID on execution
20#0 Set group ID on execution if ``#'' is 7, 5, 3, or
1 and enable mandatory locking if ``#'' is 6, 4,
2, or 0.
1000 Sets the sticky bit (see chmod(S))
0400 Read by owner
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CHMOD(C) XENIX System V CHMOD(C)
0200 Write by owner
0100 Execute (search in directory) by owner
0040 Read by group
0020 Write by group
0010 Execute (search in directory) by group
0004 Read by others
0002 Write by others
0001 Execute (search in directory) by others
0000 No permissions
Examples
Symbolic Mode
The following command causes advisory locking calls on file
to be promoted to mandatory locking:
chmod +x file
Multiple symbolic modes may be given, separated by commas,
on a single command line. The following command removes
read and write permission for group and others from file:
chmod go-rw file
The following command gives other users read and write
permission for file:
chmod o+rw file
The following command gives read permission to group and
other:
chmod g+r,o+r file
Absolute Mode
The following command gives all users read, write and
execute permission for file:
chmod 0777 file
The following command gives read and write permission to all
users for file:
chmod 0666 file
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CHMOD(C) XENIX System V CHMOD(C)
The following command gives read and write permission to the
owner of file only:
chmod 0600 file
The following example causes the file to be locked on
access:
chmod +l file
See Also
ls(C), chmod(S), locking(S), lockf(S), fcntl(S)
Notes
The setuid, setgid, and sticky bit settings are only useful
for binary executable files. They have no effect on shell
scripts.
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