Linux man pages : chmod (2)
CHMOD(2) Linux Programmer's Manual CHMOD(2)
chmod, fchmod - change permissions of a file
int chmod(const char *path, mode_t mode);
int fchmod(int fildes, mode_t mode);
The mode of the file given by path or referenced by fildes is changed.
Modes are specified by or'ing the following:
S_ISUID 04000 set user ID on execution
S_ISGID 02000 set group ID on execution
S_ISVTX 01000 sticky bit
00400 read by owner
00200 write by owner
00100 execute/search by owner
S_IRGRP 00040 read by group
S_IWGRP 00020 write by group
S_IXGRP 00010 execute/search by group
S_IROTH 00004 read by others
S_IWOTH 00002 write by others
S_IXOTH 00001 execute/search by others
The effective UID of the process must be zero or must match the owner
of the file.
If the effective UID of the process is not zero and the group of the
file does not match the effective group ID of the process or one of its
supplementary group IDs, the S_ISGID bit will be turned off, but this
will not cause an error to be returned.
Depending on the file system, set user ID and set group ID execution
bits may be turned off if a file is written. On some file systems,
only the super-user can set the sticky bit, which may have a special
meaning. For the sticky bit, and for set user ID and set group ID bits
on directories, see stat(2).
On NFS file systems, restricting the permissions will immediately
influence already open files, because the access control is done on the
server, but open files are maintained by the client. Widening the per-
missions may be delayed for other clients if attribute caching is
enabled on them.
On success, zero is returned. On error, -1 is returned, and errno is
Depending on the file system, other errors can be returned. The more
general errors for chmod are listed below:
EPERM The effective UID does not match the owner of the file, and is
EROFS The named file resides on a read-only file system.
EFAULT path points outside your accessible address space.
path is too long.
ENOENT The file does not exist.
ENOMEM Insufficient kernel memory was available.
A component of the path prefix is not a directory.
EACCES Search permission is denied on a component of the path prefix.
ELOOP Too many symbolic links were encountered in resolving path.
EIO An I/O error occurred.
The general errors for fchmod are listed below:
EBADF The file descriptor fildes is not valid.
EROFS See above.
EPERM See above.
EIO See above.
The chmod call conforms to SVr4, SVID, POSIX, X/OPEN, 4.4BSD. SVr4
documents EINTR, ENOLINK and EMULTIHOP returns, but no ENOMEM. POSIX.1
does not document EFAULT, ENOMEM, ELOOP or EIO error conditions, or the
macros S_IREAD, S_IWRITE and S_IEXEC.
The fchmod call conforms to 4.4BSD and SVr4. SVr4 documents additional
EINTR and ENOLINK error conditions. POSIX requires the fchmod function
if at least one of _POSIX_MAPPED_FILES and _POSIX_SHARED_MEMORY_OBJECTS
is defined, and documents additional ENOSYS and EINVAL error condi-
tions, but does not document EIO.
POSIX and X/OPEN do not document the sticky bit.
open(2), chown(2), execve(2), stat(2)
Linux 2.0.32 1997-12-10 CHMOD(2)