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CHMOD(2)                    BSD System Calls Manual                   CHMOD(2)

NAME
     chmod, fchmodat, fchmod -- change mode of file

SYNOPSIS
     #include <&lt;sys/stat.h>&gt;

     int
     chmod(const char *path, mode_t mode);

     int
     fchmod(int fd, mode_t mode);

     #include <&lt;sys/stat.h>&gt;
     #include <&lt;fcntl.h>&gt;

     int
     fchmodat(int fd, const char *path, mode_t mode, int flag);

DESCRIPTION
     The chmod() function sets the file permission bits of the file specified
     by the pathname path to mode.  chmod() verifies that the process owner
     (user) either owns the specified file or is the superuser.

     The mode argument is the bitwise OR of zero or more of the permission bit
     masks from the following list:

           #define S_IRWXU 0000700    /* RWX mask for owner */
           #define S_IRUSR 0000400    /* R for owner */
           #define S_IWUSR 0000200    /* W for owner */
           #define S_IXUSR 0000100    /* X for owner */

           #define S_IRWXG 0000070    /* RWX mask for group */
           #define S_IRGRP 0000040    /* R for group */
           #define S_IWGRP 0000020    /* W for group */
           #define S_IXGRP 0000010    /* X for group */

           #define S_IRWXO 0000007    /* RWX mask for other */
           #define S_IROTH 0000004    /* R for other */
           #define S_IWOTH 0000002    /* W for other */
           #define S_IXOTH 0000001    /* X for other */

           #define S_ISUID 0004000    /* set user id on execution */
           #define S_ISGID 0002000    /* set group id on execution */
           #define S_ISVTX 0001000    /* save swapped text even after use */

     If mode ISVTX (the sticky bit) is set on a file, it is ignored.

     If mode ISVTX (the sticky bit) is set on a directory, an unprivileged
     user may not delete or rename files of other users in that directory.
     The sticky bit may be set by any user on a directory which the user owns
     or has appropriate permissions.  For more details of the properties of
     the sticky bit, see sticky(8).

     Writing or changing the owner of a file turns off the set-user-ID and
     set-group-ID bits unless the user is the superuser.  This makes the sys-
     tem somewhat more secure by protecting set-user-ID (set-group-ID) files
     from remaining set-user-ID (set-group-ID) if they are modified, at the
     expense of a degree of compatibility.

     The fchmodat() function is equivalent to chmod() except in the case where
     path specifies a relative path.  In this case the file to be changed is
     determined relative to the directory associated with the file descriptor
     fd instead of the current working directory.

     If fchmodat() is passed the special value AT_FDCWD (defined in <fcntl.h>)
     in the fd parameter, the current working directory is used.  If flag is
     also zero, the behavior is identical to a call to chmod().

     The flag argument is the bitwise OR of zero or more of the following val-
     ues:

           AT_SYMLINK_NOFOLLOW  If path names a symbolic link, then the mode
                                of the symbolic link is changed.

     The fchmod() function is equivalent to chmod() except that the file whose
     permissions are changed is specified by the file descriptor fd.

RETURN VALUES
     Upon successful completion, the value 0 is returned; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS
     The chmod() and fchmodat() functions will fail and the file mode will be
     unchanged if:

     [ENOTDIR]          A component of the path prefix is not a directory.

     [ENAMETOOLONG]     A component of a pathname exceeded NAME_MAX charac-
                        ters, or an entire pathname (including the terminating
                        NUL) exceeded PATH_MAX bytes.

     [ENOENT]           The named file does not exist.

     [EACCES]           Search permission is denied for a component of the
                        path prefix.

     [EINVAL]           mode contains bits other than the file type and those
                        described above.

     [ELOOP]            Too many symbolic links were encountered in translat-
                        ing the pathname.

     [EPERM]            The effective user ID does not match the owner of the
                        file and the effective user ID is not the superuser.

     [EROFS]            The named file resides on a read-only file system.

     [EFAULT]           path points outside the process's allocated address
                        space.

     [EIO]              An I/O error occurred while reading from or writing to
                        the file system.

     Additionally, the fchmodat() function will fail if:

     [EINVAL]           The value of the flag argument was neither zero nor
                        AT_SYMLINK_NOFOLLOW.

     [EBADF]            The path argument specifies a relative path and the fd
                        argument is neither AT_FDCWD nor a valid file descrip-
                        tor.

     [ENOTDIR]          The path argument specifies a relative path and the fd
                        argument is a valid file descriptor but it does not
                        reference a directory.

     [EOPNOTSUPP]       The flag argument specifies AT_SYMLINK_NOFOLLOW on a
                        symbolic link and the file system does not support
                        that operation.

     [EACCES]           The path argument specifies a relative path but search
                        permission is denied for the directory which the fd
                        file descriptor references.

     fchmod() will fail and the file mode will be unchanged if:

     [EBADF]            The descriptor is not valid.

     [EINVAL]           fd refers to a socket, not to a file.

     [EINVAL]           mode contains bits other than the file type and those
                        described above.

     [EPERM]            The effective user ID does not match the owner of the
                        file and the effective user ID is not the superuser.

     [EROFS]            The file resides on a read-only file system.

     [EIO]              An I/O error occurred while reading from or writing to
                        the file system.

SEE ALSO
     chmod(1), chown(2), open(2), stat(2), sticky(8)

STANDARDS
     The chmod(), fchmod(), and fchmodat() functions are expected to conform
     to IEEE Std 1003.1-2008 (``POSIX.1'').

HISTORY
     The chmod() system call first appeared in Version 1 AT&T UNIX; fchmod()
     in 4.1cBSD; and fchmodat() has been available since OpenBSD 5.0.

BSD                             April 29, 2017                             BSD