CHMOD(2)

NAME
chmod, fchmod - change permissions of a file

SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>

int chmod(const char *path, mode_t mode);
int fchmod(int fildes, mode_t mode);

DESCRIPTION
The mode of the file given by path or referenced by filedes 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

    S_IRUSR (S_IREAD)
        00400 read by owner

    S_IWUSR (S_IWRITE)
        00200 write by owner

    S_IXUSR (S_IEXEC)
        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. The effective UID or GID must be appropriate for setting execution bits. 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 (i.e., for directories, a file can only be deleted by the owner or the super-user). 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 permissions may be delayed for other clients if attribute caching is enabled on them.

RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS
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 not zero.

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

EFAULT
    path points outside your accessible address space.

ENAMETOOLONG
    path is too long.

ENOENT
    The file does not exist.

ENOMEM
    Insufficient kernel memory was available.

ENOTDIR
    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.

The general errors for fchmod are listed below:

EBADF
    The descriptor is not valid.

ENOENT
    See above.

EIO A low-level I/O error occurred while modifying the inode.

CONFORMING TO
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 ENOMEM or ELOOP error conditions.

The fchmod call conforms to 4.4BSD and SVr4. SVr4 documents additional EIO, EINTR, and ENOLINK error conditions.

POSIX and X/OPEN do not document the sticky bit.

EPERM
    See above.

EROFS
    See above.

CONFORMING TO
chmod conforms to POSIX, but S_ISVTX (the sticky bit) does not, neither do the macros S_IREAD, S_IWRITE and S_IEXEC. POSIX specifies that some implementations may ignore S_ISUID and S_ISGID. Further according to POSIX, you should not attempt to set any bits which are not listed above.

SEE ALSO
open(2), chown(2), stat(2)