NAME

       chmod, fchmod - change permissions of a file

SYNOPSIS

       #include <sys/stat.h>

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

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       fchmod():
           _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
           || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L

DESCRIPTION

       These system calls change the permissions of a file.  They differ only in how the file is specified:

       * chmod()  changes  the  permissions  of  the  file  specified  whose pathname is given in path, which is
         dereferenced if it is a symbolic link.

       * fchmod() changes the permissions of the file referred to by the open file descriptor fd.

       The new file permissions are specified in mode, which is a bit mask created by  ORing  together  zero  or
       more of the following:

       S_ISUID  (04000)  set-user-ID (set process effective user ID on execve(2))

       S_ISGID  (02000)  set-group-ID  (set  process  effective  group  ID  on  execve(2); mandatory locking, as
                         described in fcntl(2); take a new file's group from parent directory, as  described  in
                         chown(2) and mkdir(2))

       S_ISVTX  (01000)  sticky bit (restricted deletion flag, as described in unlink(2))

       S_IRUSR  (00400)  read by owner

       S_IWUSR  (00200)  write by owner

       S_IXUSR  (00100)  execute/search  by  owner  ("search"  applies  for  directories, and means that entries
                         within the directory can be accessed)

       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 calling process must match the owner  of  the  file,  or  the  process  must  be
       privileged (Linux: it must have the CAP_FOWNER capability).

       If  the calling process is not privileged (Linux: does not have the CAP_FSETID capability), 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.

       As  a  security measure, depending on the filesystem, the set-user-ID and set-group-ID execution bits may
       be turned off if a file is written.  (On Linux this occurs if the  writing  process  does  not  have  the
       CAP_FSETID capability.)  On some filesystems, only the superuser 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 filesystems, 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 filesystem, other errors can be returned.  The  more  general  errors  for  chmod()  are
       listed below:

       EACCES Search permission is denied on a component of the path prefix.  (See also path_resolution(7).)

       EFAULT path points outside your accessible address space.

       EIO    An I/O error occurred.

       ELOOP  Too many symbolic links were encountered in resolving path.

       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.

       EPERM  The  effective UID does not match the owner of the file, and the process is not privileged (Linux:
              it does not have the CAP_FOWNER capability).

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

       The general errors for fchmod() are listed below:

       EBADF  The file descriptor fd is not valid.

       EIO    See above.

       EPERM  See above.

       EROFS  See above.

CONFORMING TO

       4.4BSD, SVr4, POSIX.1-2001.

SEE ALSO

       chown(2), execve(2), fchmodat(2), open(2), stat(2), path_resolution(7)

COLOPHON

       This page is part of release 3.54 of the Linux man-pages project.  A  description  of  the  project,  and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

Linux                                              2010-09-26                                           CHMOD(2)