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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)):

           || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L


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

       * 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.


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


       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

       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 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.


       4.4BSD, SVr4, POSIX.1-2001.


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


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