chmod [-fR] mode file ...
Only the owner of a file or a user with appropriate privileges can change the mode of a file.
| 4000 | set-user-ID-on-execution; see NOTES later in this topic |
| 2000 | set-group-ID-on-execution; see NOTES later in this topic |
| 1000 | sticky bit, see chmod(2) |
| 0400 | read by owner |
| 0200 | write by owner |
| 0100 | execute (or search for directories) by owner |
| 0040 | read by group |
| 0020 | write by group |
| 0010 | execute/search by group |
| 0004 | read by others |
| 0002 | write by others |
| 0001 | execute/search by others |
The read, write, and execute/search values for group and others are encoded as described for owner.
The symbolic mode is described by the following grammar:
mode ::= clause [, clause ...]
clause ::= [who ...] [action ...] last_action
action ::= op [perm ...]
last_action ::= op [perm ...]
who ::= a | u | g | o
op ::= + | - | =
perm ::= r | 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; see NOTES later in this topic. |
| 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 | User permission bits in the original file's mode. |
| g | Group permission bits in the original file's mode. |
| o | Other permission bits in the original file's mode. |
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.
| 644 | Make a file readable by anyone and writeable 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 | Make a file readable/executable by everyone and writeable by the owner only. |
| Same as 755 | |
| u=rwx,go=rx | Same as 755 |
| go= | Clear all mode bits for the group and others. |
| g=u-w | Set the group bits equal to the user bits, but clear the group write bit. |
By default, Interix does not execute files with the set-user-ID (setuid) or set-group-ID (setgid) mode bit set for security reasons. If an attempt is made to execute such a file, the ENOSETUID error is returned. For more information and and instructions for enabling execution of files with these mode bits set, see The superuser account and appropriate privileges in Windows Services for UNIX Help.
chgrp(1)
chown(1)
umask(1)