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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

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  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 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 mean-
       ing.  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 permissions
       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 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-05-26                          CHMOD(2)