File: coreutils.info, Node: chmod invocation, Next: touch invocation, Prev: chgrp invocation, Up: Changing file attributes 13.3 'chmod': Change access permissions ======================================= 'chmod' 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 *note 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 *note Common options::. '-c' '--changes' Verbosely describe the action for each FILE whose permissions actually changes. '-f' '--silent' '--quiet' Do not print error messages about files whose permissions cannot be changed. '--preserve-root' Fail upon any attempt to recursively change the root directory, '/'. Without '--recursive', this option has no effect. *Note Treating / specially::. '--no-preserve-root' Cancel the effect of any preceding '--preserve-root' option. *Note Treating / specially::. '-v' '--verbose' Verbosely describe the action or non-action taken for every FILE. '--reference=REF_FILE' Change the mode of each FILE to be the same as that of REF_FILE. *Note 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. '-R' '--recursive' 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
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