chmod(2)							 chmod(2)

NAME [Toc]

 chmod, fchmod - change mode of file

SYNOPSIS [Toc]

 #include <sys/types.h>
 #include <sys/stat.h>
 int chmod(const char *path, mode_t	mode);
 int fchmod(int fildes, mode_t mode);

DESCRIPTION [Toc]

 chmod and fchmod set the access permission	portion	of the mode of the
 file whose	name is	given by path or referenced by the descriptor fildes
 to	the bit	pattern	contained in mode. If path or fildes are symbolic
 links, the	access permissions of the target of the	symbolic links are
 set. Access permission bits are interpreted as follows:
 S_ISUID 04000 Set user ID on execution.
 S_ISGID 020#0 Set group ID on execution if # is 7, 5, 3,	or 1
		 Enable mandatory file/record locking if # is 6, 4,	2, or 0
 S_ISVTX 01000 Save text image after execution (a.k.a. Sticky bit).
 S_IRWXU 00700 Read, write, execute by owner.
 S_IRUSR 00400 Read by owner.
 S_IWUSR 00200 Write by owner.
 S_IXUSR 00100 Execute (search if	a directory) by	owner.
 S_IRWXG 00070 Read, write, execute by group.
 S_IRGRP 00040 Read by group.
 S_IWGRP 00020 Write by group.
 S_IXGRP 00010 Execute by	group.
 S_IRWXO 00007 Read, write, execute (search) by others.
 S_IROTH 00004 Read by others.
 S_IWOTH 00002 Write by others
 S_IXOTH 00001 Execute by	others.
 Modes are constructed by OR'ing the access	permission bits.
 The effective user	ID of the process must match the owner of the file or
 the process must be super-user to change the mode of a file.
 If	the effective user ID of the process is	not super-user,	the sticky bit
 is	cleared	for any	non-directory argument.
 If	the effective group ID of the process does not match the group ID of
 the file, and the process is not super-user the mode bit 02000 (set group
 ID	on execution) is cleared.
 If	a directory is writable	and the	sticky bit, S_ISVTX, is	set on the
 directory,	a process may remove or	rename files within that directory
 only if one or more of the	following is true [see unlink(2) and
 rename(2)]:
									Page 1
chmod(2)							 chmod(2)
	 the effective	user ID	of the process is the same as that of the
	 owner	ID of the file
	 the effective	user ID	of the process is the same as that of the
	 owner	ID of the directory
	 the process is a super-user.
 Note that the group id of the process and file are	not taken into account
 by	the rules above. A process will only be able to remove	a file in a
 sticky directory based upon its effective user ID,	not its	group ID.
 In	releases of IRIX before	6.2, a process could also remove or rename
 files within a directory with the sticky bit set if the process had write
 permission	for the	file. This has	been changed in	accordance with	the
 X/Open XPG4.2 standard, but the old behavior can be enabled via the
 xpg4_sticky_bit kernel tunable variable.
 If	the sticky bit,	S_ISVTX, is set	on a file that is a dynamic loader for
 an	ELF executable,	then when the executable is execed the old process's
 read only address spaces will be made available to	the dynamic loader in
 the new process. This can	improve	program	start up time considerably.
 The setting of the	sticky bit on any other	file has no effect.
 If	the mode bit 02000 (set	group ID on execution) is set, the mode	bit
 00010 (execute or search by group)	is not set, and	the file is a regular
 file, file	and record locks will be mandatory. Future calls to open(2),
 creat(2), read(2),	and write(2) will carry	implicit locks,	and may	fail
 or	block depending	on the presence	of other locks on the file. Mapped
 file access is not	affected by mandatory locks.
 If	the mode bit 02000 is set on a directory, then any files created in
 that directory will take on the group ID of the directory rather than the
 group ID of the calling process. mount(1M) may be	used to	enable this
 feature regardless	of the mode of the directory. [See fstab(4)].
 Mandatory locking is not supported	on NFS or CacheFS.
 Upon successful completion, chmod and fchmod mark for update the st_ctime
 field of the file.
 chmod will	fail and the file mode will be unchanged if one	or more	of the
 following are true:
 EACCES	 Search permission is denied	on a component of the path
		 prefix of path.
 EACCES	 Write permission on	the named file is denied.
									Page 2
chmod(2)							 chmod(2)
 EFAULT	 path points	outside	the allocated address space of the
		 process.
 EINTR	 A signal was caught	during execution of the	system call.
 EIO	 An I/O error occurred while	reading	from or	writing	to the
		 file system.
 ELOOP	 Too	many symbolic links were encountered in	translating
		 path.
 EMULTIHOP	 Components of path require hopping to multiple remote
		 machines and file system type does not allow it.
 ENAMETOOLONG The	length of the path argument exceeds {PATH_MAX},	or the
		 length of a	path component exceeds {NAME_MAX} while
		 _POSIX_NO_TRUNC is in effect.
 ENOTDIR	 A component	of the prefix of path is not a directory.
 ENOENT	 Either a component of the path prefix, or the file
		 referred to	by path	does not exist or is a null pathname.
 ENOLINK	 path points	to a remote machine and	the link to that
		 machine is no longer active.
 ETIMEDOUT	 The	named file is located on a remote file system which is
		 not	available [see intro(2)].
 EPERM	 The	effective user ID does not match the owner of the file
		 and	the process is not super-user.
 EROFS	 The	file referred to by path resides on a read-only	file
		 system.
 fchmod will fail and the file mode	will be	unchanged if:
 EBADF	 fildes is not an open file descriptor
 EIO	 An I/O error occurred while	reading	from or	writing	to the
		 file system.
 EINTR	 A signal was caught	during execution of the	fchmod system
		 call.
 ENOLINK	 fildes refers to a remote machine and the link to that
		 machine is no longer active.
 ETIMEDOUT	 fildes refers to a file on a remote	file system which is
		 not	available [see intro(2)].
									Page 3
chmod(2)							 chmod(2)
 EPERM	 The	effective user ID does not match the owner of the file
		 and	the process is not super-user.
 EROFS	 The	file referred to by fildes resides on a	read-only file
		 system.
 EINVAL	 The	file referred to by fildes resides on NFS or CacheFS
		 and	mandatory locking is being enabled.

SEE ALSO [Toc]

 chmod(1), access(2), chown(2), creat(2), exec(2), fcntl(2), mknod(2),
 open(2), read(2), stat(2),	write(2), mkfifo(3C), stat(5)

DIAGNOSTICS [Toc]

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

BUGS [Toc]

 Due to the	overloading of various permission bits,	the silent turning off
 of	the set	group ID on execution bit under	the above mentioned
 circumstances may in fact have disabled mandatory file/record locking
 (for files) or group inheritance (for directories). The only way to
 determine if chmod	really worked in these cases is	to stat(2) the file.
									PPPPaaaaggggeeee 4444