nnfs.txt

Non-Networked File System在几个非网络的（或慢网络的）Unix 计算机上提供了一个兼容的文件系统。

                                     nnfs2

Name

   nnfs2 -- Synchronise filesystems between Non-Networked hosts

Synopsis

   nnfs2 { --no-x11} [--add-first directory-name | --add directory-name |
   --add-nickname directory-name]

   nnfs2 [--help | --licence]

INTRODUCTION

   The NNFS goal is to provide to ``one'' user a consistent file system
   over all the hosts used by the user.

   With hosts connected on a LAN you must use NFS instead of NNFS. In the
   case of hosts not connected by a network or connected by a slow
   network (modem) NFS is not the answer.

   With NNFS, the files are duplicated on all the computers. The up to
   date files are on the computer on which the user works. The NNFS
   filesystem is stored on the NNFS medium. Usually the NNFS medium is a
   floppy disk, it could be whatever you want (easily customisable), if
   there is much data, several floppies will be asked.

   When the user stops his work on a computer, he runs as last command:
   nnfs2. Then all his modifications (change, creation, deletion) are
   recorded on the NNFS medium.

   When the user starts to work on a computer, he runs as first command:
   nnfs2. Then all modifications (change, creation, deletion) stored on
   the NNFS medium are retrieved on current system.

   If the user forgot to run an update, nnfs2 will nevertheless optimally
   work. The only drawback is that some files will not be up to date on
   the host used by the user.

   It is also possible to have a numbered backup of modified/deleted
   files. So you cannot lose a file when you run nnfs2 (because the file
   is modified/deleted on another host)

USAGE

   nnfs2 has a text and a graphical user interface. If you run the
   command for the first time or with a NNFS medium formatted or not, the
   command will provide contextual informations and help and will ask
   contextual questions. The graphical user interface allows you to edit
   the configuration.

   The interactive help is extensive and guide the user. This
   documentation is here to give general principles.

   By default the nnfs2 works with standards tools: floppy disk and gzip.
   The floppy disk access is done via system dependent commands (IRIX,
   AIX, HPUX and mcopy in the other cases). If you want to change these
   defaults, see the configuration section.

   As the default configurations use floppy disk, the nnfs2 default
   filter does not synchronise big files or ``garbage'' files. If you
   want to change these defaults, see the configuration section.

   It is not recommended to continue to modify files while nnfs2 is
   running. It is not dangerous but the result is unpredictable.

   Be carefull, some applications wrote their data on disk only when you
   stop them. So you must stop these applications before running nnfs2.
   For example netscape wrote some folder information only when you quit
   the program, so you must run nnfs2 only if netscape is not running.

To do before using nnfs2

   If the file hierarchy you want to synchronise is yet identical on all
   the hosts you can go to the next section. The root of the file
   hierarchy may have a different name on each host. To avoid problems
   you should use only relative internal symbolic links, so the links are
   correct on all the hosts.

   If the files hierarchy are not identical, you have two solutions:

     * You create yourself an identical hierarchy on all the hosts. The
       file modification date should be identical on all the hosts.
     * Or, you let nnfs2 create the identical hierarchy on all the hosts.
       In this case, a hierarchy made of the union of all the files is
       created, conflicts are solved using the modification date. It is
       the only case where the modification date is used to solve
       conflicts.

Initialisations

   When you run the nnfs2 command on an host not known by the NNFS
   filesystem it will explain you how to add the host in the NNFS
   filesystem.

   If the NNFS filesystem does not fit in one medium, you will be asked
   to introduce medium.

   Now, the initialisation for 2 hosts named A and B will be detailed for
   the 2 user interfaces.

Initialisations with X11 interface

   First run on host A.

     * You click on: Continue without reading the medium
     * you enter the local name of the hierarchy to synchronise,
     * you click on: Continue the update,
     * you click on: Medium AAA is ready for writing,
     * you click on: Quit

   Second run on host B, assuming medium is ready.

     * You click on: Continue the update
     * you enter the local name of the hierarchy to synchronise,
     * you click on: Continue the update,
     * you click on: Quit

   Normal run when initialisations are done, assuming medium is ready.

     * You click on: Continue the update
     * you click on: Continue the update,
     * you click on: Quit

Initialisations with text interface

   First run on host A.

     * You type: nnfs2 --add-first dirname
     * You answer: c return to continue the update
     * You hit : return when medium is ready

   Second run on host B, assuming medium is ready.

     * You type: nnfs2 --add dirname
     * You answer: c return to continue the update

   Normal run when initialisations are done, assuming medium is ready.

     * You type: nnfs2
     * You answer: c return to continue the update

How to recover from NNFS medium read failure

   If there is a read error you can rerun nnfs2 a few times with the hope
   that the error will vanish. If it is not the case, put the bad medium
   in a trash, take a new one and create immediately a new NNFS
   filesystem with the current host.

   If the read error is before you start to work on an host. Try to not
   work on non-synchronized file in order to avoid future conflicts. Run
   nnfs2 as always before stopping to work on the host.

   If the read error is before you leave an host. You will want to copy
   the file modified by your session on the other host. To do so, modify
   all the file you want to synchronise and rerun nnfs2 on the host. For
   example by running find . -mtime -1 -print | xargs touch. If you do
   not do this, these files will be synchronised but only after adding
   the other host on NNFS filesystem, a run on local the host and a run
   on the other host.

   My experience about floppies is that there is floppies usable only 2
   or 3 times and some usable hundreds of time. Even if they are from the
   same box.

Historised backups

   Each time you run nnfs2 the files deleted or modified are moved in a
   directory. This directory is not mirrored!

   Example 1. Archiving modified files in default directory

   Current date: Sun Sep 16 14:57:47 CEST 2001

   Modified file: foo/bar/Makefile

   Historised file: .nnfs/history/2001_09/16_14:57.47/foo/bar/Makefile

   So you can easily remove old historised files by date.

Conflicts

   If you don't run nnfs2 before and after working, some update conflicts
   may be raised if you work on the same files.

   Example 2. A simple conflict

     * You run nnfs2 on host A
     * You modify foo on host A
     * You run nnfs2 on host A
     * You modify foo on host B
     * You run nnfs2 on host B (you should have done this before
       modifying the file)

   The conflict solving method is straightforward, the remote conflicting
   file is always copied on local host. If you don't agree, you can
   retrieve the local file content from the .nnfs/history directory.

   This method is not used to solve conflict when adding a new host. In
   this case, the most recent file is copied over the old ones