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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


       The mode of the file given by path or referenced by fd 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   00400 read by owner

              S_IWUSR   00200 write by owner

              S_IXUSR   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 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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