FS(4)                                                       FS(4)

     NAME
          fs - file server, dump

     SYNOPSIS
          none

     DESCRIPTION
          The file server was the main file system for Plan 9.  It was
          a stand-alone system that ran on a separate computer.  It
          served the Plan 9 protocol via the IL/IP protocols on Ether-
          nets.  The name of the main file server at Murray Hill was
          emelie.

          The file server normally requires all users except `none' to
          provide authentication tickets on each attach(5). This can
          be disabled using the noauth configuration command (see
          fsconfig(8)).

          The group numbered 9999, normally called noworld, is special
          on the file server.  Any user belonging to that group has
          attenuated access privileges.  Specifically, when checking
          such a user's access to files, the file's permission bits
          are first ANDed with 0770 for normal files or 0771 for
          directories.  The effect is to deny world access permissions
          to noworld users, except when walking directories.

          The user none is always allowed to attach to emelie without
          authentication but has minimal permissions.

          Emelie maintains three file systems on a combination of
          disks and write-once-read-many (WORM) magneto-optical disks.

          other
               is a simple disk-based file system not backed by the
               worm.

          main is a worm-based file system with a disk-based look-
               aside cache.  The disk cache holds modified worm blocks
               to overcome the write-once property of the worm.  The
               cache also holds recently accessed non-modified blocks
               to speed up the effective access time of the worm.
               Occasionally (usually daily at 5AM) the modified blocks
               in the disk cache are dumped. At this time, traffic to
               the file system is halted and the modified blocks are
               relabeled to the unwritten portion of the worm.  After
               the dump, the file system traffic is continued and the
               relabeled blocks are copied to the worm by a background
               process.

          dump Each time the main file system is dumped, its root is

     FS(4)                                                       FS(4)

               appended to a subdirectory of the dump file system.
               Since the dump file system is not mirrored with a disk
               cache, it is read-only.  The name of the newly added
               root is created from the date of the dump: /yyyy/mmdds.
               Here yyyy is the full year, mm is the month number, dd
               is the day number and s is a sequence number if more
               than one dump is done in a day.  For the first dump, s
               is null.  For the subsequent dumps s is 1, 2, 3, etc.

               The root of the main file system that is frozen on the
               first dump of March 1, 1992 will be named /1992/0301/
               in the dump file system.

     EXAMPLES
          Place the root of the dump file system on /n/dump and show
          the modified times of the MIPS C compiler over all dumps in
          February, 1992:

               9fs dump
               ls -l /n/dump/1992/02??/mips/bin/vc

          To get only one line of output for each version of the com-
          piler:

               ls -lp /n/dump/1992/02??/mips/bin/vc | uniq

          Make the other file system available in directory
          /n/emelieother:

               mount -c /srv/boot /n/emelieother other

     SOURCE
          /sys/src/fs

     SEE ALSO
          yesterday(1), cwfs(4), srv(4), fs(8)
          Sean Quinlan, ``A Cached WORM File System'', Software -
          Practice and Experience, December, 1991

     BUGS
          For the moment, the file server serves both the old (third
          edition) and new (fourth edition) versions of 9P, deciding
          which to serve by sniffing the first packet on each connec-
          tion.

          Required IL, thus now deprecated.