chmod
: Change access permissionschmod
changes the access permissions of the named files. Synopsis:
chmod [option]… {mode | --reference=ref_file} file…
chmod
never changes the permissions of symbolic links, since
the chmod
system call cannot change their permissions.
This is not a problem since the permissions of symbolic links are
never used. However, for each symbolic link listed on the command
line, chmod
changes the permissions of the pointed-to file.
In contrast, chmod
ignores symbolic links encountered during
recursive directory traversals.
Only a process whose effective user ID matches the user ID of the file, or a process with appropriate privileges, is permitted to change the file mode bits of a file.
A successful use of chmod
clears the set-group-ID bit of a
regular file if the file’s group ID does not match the user’s
effective group ID or one of the user’s supplementary group IDs,
unless the user has appropriate privileges. Additional restrictions
may cause the set-user-ID and set-group-ID bits of mode or
ref_file to be ignored. This behavior depends on the policy and
functionality of the underlying chmod
system call. When in
doubt, check the underlying system behavior.
If used, mode specifies the new file mode bits.
For details, see the section on File permissions.
If you really want mode to have a leading ‘-’, you should
use -- first, e.g., ‘chmod -- -w file’. Typically,
though, ‘chmod a-w file’ is preferable, and chmod -w
file
(without the --) complains if it behaves differently
from what ‘chmod a-w file’ would do.
The program accepts the following options. Also see Common options.
Verbosely describe the action for each file whose permissions actually change.
Do not print error messages about files whose permissions cannot be changed.
Fail upon any attempt to recursively change the root directory, /. Without --recursive, this option has no effect. See Treating / specially.
Cancel the effect of any preceding --preserve-root option. See Treating / specially.
Verbosely describe the action or non-action taken for every file.
Change the mode of each file to be the same as that of ref_file. See File permissions. If ref_file is a symbolic link, do not use the mode of the symbolic link, but rather that of the file it refers to.
Recursively change permissions of directories and their contents.
An exit status of zero indicates success, and a nonzero value indicates failure.
Examples:
# Change file permissions of FOO to be world readable # and user writable, with no other permissions. chmod 644 foo chmod a=r,u+w foo # Add user and group execute permissions to FOO. chmod +110 file chmod ug+x file # Set file permissions of DIR and subsidiary files to # be the umask default, assuming execute permissions for # directories and for files already executable. chmod -R a=,+rwX dir