chmod, fchmod - change permissions of a file


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

     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

          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.

     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 (e.g., for direc-
     tories, a file can only be  deleted  by  the  owner  or  the

     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.


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


     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.

             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  resolv-
             ing 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

     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
     defined, and documents additional ENOSYS  and  EINVAL  error
     conditions, but does not document EIO.

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


     open(2), chown(2), stat(2)