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       chmod, fchmod - change permissions of a file


       #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


       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

       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

       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 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

       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:

       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.

              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.

       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.


       4.4BSD, SVr4, POSIX.1-2001.


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


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