chmod(2) - NetBSD Manual Pages

Command:
Section:
Arch:
Collection:
>>>
CHMOD(2)                  NetBSD System Calls Manual                  CHMOD(2)


NAME

     chmod, lchmod, fchmod -- change mode of file


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <sys/stat.h>

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

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

     int
     fchmod(int fd, mode_t mode);


DESCRIPTION

     The function chmod() sets the file permission bits of the file specified
     by the pathname path to mode.  fchmod() sets the permission bits of the
     specified file descriptor fd.  lchmod() is like chmod() except in the
     case where the named file is a symbolic link, in which case lchmod() sets
     the permission bits of the link, while chmod() sets the bits of the file
     the link references.  chmod() verifies that the process owner (user)
     either owns the file specified by path (or fd), or is the super-user.  A
     mode is created from or'd permission bit masks defined in <sys/stat.h>:
           #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 regular file, it histori-
     cally meant that the system should save a shareable copy of the program
     text in the swap area.  When applied to commonly used programs like the
     shell or editor, this would decrease memory usage and startup time.  In
     NetBSD, the sticky bit may still be set on regular files by the super-
     user, but has no effect.  The historical meaning became obsolete in the
     1980s with the advent of memory-mapped executables, and is only docu-
     mented as a matter of historical interest.

     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 information about the properties of the sticky bit, see
     sticky(7).

     Changing the owner of a file turns off the set-user-id and set-group-id
     bits; writing to a file turns off the set-user-id and set-group-id bits
     unless the user is the super-user.  This makes the system 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.


RETURN VALUES

     Upon successful completion, a value of 0 is returned.  Otherwise, a value
     of -1 is returned and errno is set to indicate the error.


ERRORS

     chmod() and lchmod() 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 path name exceeded {PATH_MAX} char-
                        acters.

     [ENOENT]           The named file does not exist.

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

     [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 super-user.

     [EPERM]            The mode includes the setgid bit (S_ISGID) but the
                        file's group is neither the effective group ID nor is
                        it in the group access list.

     [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.

     [EFTYPE]           The effective user ID is not the super-user, the mode
                        includes the sticky bit (S_ISVTX), and path does not
                        refer to a directory.

     fchmod() will fail if:

     [EBADF]            The descriptor is not valid.

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

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

     [EPERM]            The mode includes the setgid bit (S_ISGID) but the
                        file's group is neither the effective group ID nor is
                        it in the group access list.

     [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.

     [EFTYPE]           The effective user ID is not the super-user, the mode
                        includes the sticky bit (S_ISVTX), and fd does not
                        refer to a directory.


SEE ALSO

     chmod(1), chflags(2), chown(2), open(2), stat(2), getmode(3), setmode(3),
     sticky(7), symlink(7)


STANDARDS

     The chmod() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'').


HISTORY

     The fchmod() function call appeared in 4.2BSD.  The lchmod() function
     call appeared in NetBSD 1.3.

NetBSD 5.1.5                    January 4, 2009                   NetBSD 5.1.5