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chmod -- change file modes
SYNOPSIS
chmod [-fhv] [-R [-H | -L | -P]] mode file ...
DESCRIPTION
The chmod utility modifies the file mode bits of the listed files as
specified by the mode operand.
The options are as follows:
-f Do not display a diagnostic message if chmod could not modify the
mode for file, nor modify the exit status to reflect such fail-
ures.
-H If the -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.)
-h If the file is a symbolic link, change the mode of the link it-
self rather than the file that the link points to.
-L If the -R option is specified, all symbolic links are followed.
-P If the -R option is specified, no symbolic links are followed.
This is the default.
-R Change the modes of the file hierarchies rooted in the files, in-
stead of just the files themselves. Beware of unintentionally
matching the ".." hard link to the parent directory when using
wildcards like ".*".
-v Cause chmod to be verbose, showing filenames as the mode is modi-
fied. If the -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.
The -H, -L and -P options are ignored unless the -R option is specified.
In addition, these options override each other and the command's actions
are determined by the last one specified.
If chmod receives a SIGINFO signal (see the status argument for stty(1)),
then the current filename as well as the old and new modes are displayed.
Only the owner of a file or the super-user is permitted to change the
mode of a file.
EXIT STATUS
The chmod utility exits 0 on success, and >0 if an error occurs.
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:
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 chmod(2)
and the suiddir option to mount(8).
2000 (the setgid bit). Executable files with this bit set will
run with effective gid set to the gid of the file owner.
1000 (the sticky bit). See chmod(2) and sticky(7).
0400 Allow read by owner.
0200 Allow write by owner.
0100 For files, allow execution by owner. For directories, al-
low the owner to search in the directory.
0040 Allow read by group members.
0020 Allow write by group members.
0010 For files, allow execution by group members. For directo-
ries, allow group members to search in the directory.
0004 Allow read by others.
0002 Allow write by others.
0001 For files, allow execution by others. For directories al-
low others to search in the directory.
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).
The symbolic mode is described by the following grammar:
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
The who symbols ``u'', ``g'', and ``o'' specify the user, group, and
other parts of the mode bits, respectively. The who symbol ``a'' is
equivalent to ``ugo''.
The perm symbols represent the portions of the mode bits as follows:
r The read bits.
s The set-user-ID-on-execution and set-group-ID-on-execution
bits.
t The sticky bit.
w The write bits.
x The execute/search bits.
X The execute/search bits if the file is a directory or any
of the execute/search bits are set in the original (unmodi-
fied) mode. Operations with the perm symbol ``X'' are only
meaningful in conjunction with the op symbol ``+'', and are
ignored in all other cases.
u The user permission bits in the original mode of the file.
g The group permission bits in the original mode of the file.
o The other permission bits in the original mode of the file.
The op symbols represent the operation performed, as follows:
+ If no value is supplied for perm, the ``+'' operation has no ef-
fect. If no value is supplied for who, each permission bit speci-
fied in perm, for which the corresponding bit in the file mode cre-
ation mask (see umask(2)) is clear, is set. Otherwise, the mode
bits represented by the specified who and perm values are set.
- If no value is supplied for perm, the ``-'' operation has no ef-
fect. If no value is supplied for who, each permission bit speci-
fied in perm, for which the corresponding bit in the file mode cre-
ation mask is set, is cleared. Otherwise, the mode bits repre-
sented by the specified who and perm values are cleared.
= The mode bits specified by the who value are cleared, or, if no who
value is specified, the owner, group and other mode bits are
cleared. Then, if no value is supplied for who, each permission
bit specified in perm, for which the corresponding bit in the file
mode creation mask is clear, is set. Otherwise, the mode bits rep-
resented by the specified who and perm values are set.
Each 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 speci-
fied.
Operations upon the other permissions only (specified by the symbol ``o''
by itself), in combination with the perm symbols ``s'' or ``t'', are ig-
nored.
The ``w'' permission on directories will permit file creation, reloca-
tion, and copy into that directory. Files created within the directory
itself will inherit its group ID.
EXAMPLES
644 make a file readable by anyone and writable by the owner
only.
go-w deny write permission to group and others.
=rw,+X set the read and write permissions to the usual defaults,
but retain any execute permissions that are currently set.
+X make a directory or file searchable/executable by everyone
if it is already searchable/executable by anyone.
755
u=rwx,go=rx
u=rwx,go=u-w make a file readable/executable by everyone and writable by
the owner only.
go= clear all mode bits for group and others.
g=u-w set the group bits equal to the user bits, but clear the
group write bit.
COMPATIBILITY
The -v option is non-standard and its use in scripts is not recommended.
SEE ALSO
chflags(1), install(1), setfacl(1), chmod(2), stat(2), umask(2), fts(3),
setmode(3), sticky(7), symlink(7), chown(8), mount(8)
STANDARDS
The chmod utility is expected to be IEEE Std 1003.2 ("POSIX.2") compati-
ble with the exception of the perm symbol "t" which is not included in
that standard.
HISTORY
A chmod command appeared in Version 1 AT&T UNIX.
BUGS
There is no perm option for the naughty bits of a horse.
FreeBSD 13.0 January 7, 2017 FreeBSD 13.0
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