huschi.net

CHMOD(2)                   Linux Programmer's Manual                  CHMOD(2)

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 direc-
                         tory, 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 direc-
                         tories, 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 file system, 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 file systems, 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  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.
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:
       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 file system.
       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 3.53 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)