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

       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)):

	   _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
	   || /* 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 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 direc‐
			 tory, 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 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

       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.

       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)

       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

Linux				  2010-09-26			      CHMOD(2)

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