NAME
chmod - change mode of file

SYNOPSIS
chmod(path, mode)
const char *path;
int mode;

fchmod(fd, mode)
int fd, mode;

DESCRIPTION
The file whose name is given by path or referenced by the
descriptor fd has its mode changed to mode. Modes are constructed
by or’ing together some combination of the following, defined in
<sys/inode.h>:

ISUID 04000 set user ID on execution
ISGID 02000 set group ID on execution
ISVTX 01000 ‘sticky bit’ (see below)
IREAD 00400 read by owner
IWRITE 00200 write by owner
IEXEC 00100 execute (search on directory) by owner
00070 read, write, execute (search) by group
00007 read, write, execute (search) by others

If an executable file is set up for sharing (this is the default)
then mode ISVTX (the ‘sticky bit’) prevents the system from
abandoning the swap-space image of the program-text portion of the
file when its last user terminates. Ability to set this bit on
executable files is restricted to the super-user.

If mode ISVTX (the ‘sticky bit’) is set on a directory, an
unprivileged user may not delete or rename files of other users in
that directory. For more details of the properties of the sticky
bit, see sticky(8).

Only the owner of a file (or the super-user) may change the mode.

Writing or changing the owner of a file turns off the set-user-id
and set-group-id bits unless the user is the super-user. This
makes the system somewhat more secure by protecting set-user-id
(set-group-id) files from remaining set-user-id (set-group-id) if
they are modified, at the expense of a degree of compatibility.

RETURN VALUE
Upon successful completion, a value of 0 is returned. Otherwise, a
value of -1 is returned and errno is set to indicate the error.

ERRORS
Chmod will fail and the file mode will be unchanged if:

[ENOTDIR] A component of the path prefix is not a directory.

[EINVAL] The pathname contains a character with the high-
order bit set.

[ENAMETOOLONG] A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.

[ENOENT] The named file does not exist.

[EACCES] Search permission is denied for a component of the
path prefix.

[ELOOP] Too many symbolic links were encountered in
translating the pathname.

[EPERM] The effective user ID does not match the owner of
the file and the effective user ID is not the
super-user.

[EROFS] The named file resides on a read-only file system.

[EFAULT] Path points outside the process’s allocated address
space.

[EIO] An I/O error occurred while reading from or writing
to the file system.

Fchmod will fail if:

[EBADF] The descriptor is not valid.

[EINVAL] Fd refers to a socket, not to a file.

[EROFS] The file resides on a read-only file system.

[EIO] An I/O error occurred while reading from or writing
to the file system.

SEE ALSO
chmod(1), open(2), chown(2), stat(2), sticky(8)