Do not display a diagnostic message if chmod could not modify the mode for file, nor modify the exit status to reflect such failures.
-H
If the -R option is specified, symbolic links on the command line are followed. (Symbolic links encountered in the tree traversal are not followed by default.)
-h
If the file is a symbolic link, change the mode of the link itself 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 instead of just the files themselves.
-v
Cause chmod to be verbose, showing filenames as the mode is modified. 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.
Only the owner of a file or the super-user is permitted to change the mode of a file.
(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(8).
0400
Allow read by owner.
0200
Allow write by owner.
0100
For files, allow execution by owner. For directories, allow 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 directories, 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 allow 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 (unmodified) 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 effect. 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 represented by the specified who and perm values are set.
-
If no value is supplied for perm, the ‘‘-’’ operation has no effect. 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 cleared. Otherwise, the mode bits represented 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 represented 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 specified.
Operations upon the other permissions only (specified by the symbol ‘‘o’’ by itself), in combination with the perm symbols ‘‘s’’ or ‘‘t’’, are ignored.
