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  1. Name
  2. Motivation
  3. inotify vs fanotify
  4. Installing
  5. How to use
  6. Example of usage
  7. Recommended configuration
  8. Known issues
  9. Support
  10. Developing

1. Name

Why "clsync"? The first name of the utility was "insync" (due to inotify), but then I suggested to use "fanotify" instead of "inotify" and utility was been renamed to "fasync". After that I started to intensively write the program. However I faced with some problems in "fanotify", so I was have to temporary fallback to "inotify", then I decided, that the best name is "Runtime Sync" or "Live Sync", but "rtsync" is a name of some corporation, and "lsync" is busy by "lsyncd" project (""). So I called it "clsync", that should be interpreted as "lsync, but on c" due to "lsyncd" that written on "LUA" and may be used for the same purposes.

UPD: Also I was have to add somekind of clustering support. It's multicast notifing subsystem to prevent loops on bidirection syncing. So "clsync" also can be interpreted as "cluster live sync". ;)

2. Motivation

This utility was been writted for two purposes:

  • for making failover clusters
  • for making backups of them

To do failover cluster I've tried a lot of different solutions, like "simple rsync by cron", "glusterfs", "ocfs2 over drbd", "common mirrorable external storage", "incron + perl + rsync", "inosync", "lsyncd" and so on. Currently we are using "lsyncd", "ceph" and "ocfs2 over drbd". However all of this solutions doesn't arrange me, so I was have to write own utility for this purpose.

To do backups we also tried a lot of different solution, and again I was have to write own utility for this purpose.

The best known (for me) replacement for this utility is "lsyncd", however:

  • It's code is >½ on LUA. There a lot of problems connected with it, for example:
    • It's more difficult to maintain the code with ordinary sysadmin.
    • It really eats 100% CPU sometimes.
    • It requires LUA libs, that cannot be easily installed to few of our systems.
  • It's a little buggy. That may be easily fixed for our cases, but LUA. :(
  • It doesn't support pthread or something like that. It's necessary to serve huge directories with a lot of containers right.
  • It cannot run rsync for a pack of files. It runs rsync for every event. :(
  • Sometimes, it's too complex in configuration for our situation.
  • It can't set another event-collecting delay for big files. We don't want to sync big files (>1GiB) so often as ordinary files.

Sorry, if I'm wrong. Let me know if it is, please :). "lsyncd" - is really good and useful utility, just it's not appropriate for us.

3. inotify vs fanotify:

It's said, that fanotify is much better, than inotify. So I started to write this program with using of fanotify. However I encountered the problem, that fanotify was unable to catch some important events at the moment of writing the program, like "directory creation" or "file deletion". So I switched to "inotify", leaving the code for "fanotify" in the safety... So, don't use "fanotify" in this utility ;).

4. Installing

First of all, you should install dependencies to compile clsync. As you can see from GNUmakefile clsync depends only on "glib-2.0", so on debian-like systems you should execute something like "apt-get install libglib2.0-dev".

Next step is generating Makefile. To do that usually it's enought to execute "autoreconf -i && ./configure".

Next step is compiling. To compile usually it's enough to execute "make".

Next step in installing. To install usually it's enough to execute "su -c 'make install'".

Also, debian-users can use my repository to install the clsync: deb [arch=amd64] unstable main

5. How to use

How to use is described in "man" ;). What is not described, you can ask me personally (see "Support").

6. Example of usage

Example of usage, that works on my PC is in directory "example". Just run "" and try to create/modify/delete files/dirs in "example/testdir/from". All modifications should appear (with some delay) in directory "example/testdir/to" ;)

7. Recommended configuration

First of all, recommended and not recommended options are notices in the manpage.

However let's describe 4 situations:

  • The simpliest usage (syncing from "/tmp/fromdir" to "/tmp/todir" with delay about 30 seconds): clsync -RR -d /dev/shm/clsync /tmp/fromdir $(which rsync) /dev/zero /tmp/todir

  • You're backing-up over very slow channel: clsync -l backup -R -d /dev/shm/clsync -t 600 -T 3600 -B $[1024 * 1024 * 16] /home/user /home/clsync/bin/ /home/clsync/clsync-rules

This will minimize network traffic. And pthread-ing is removed due to rarely updating.

  • You're syncing ordinary web-server over 1Gbs channel: clsync -l mirror -p -R -d /dev/shm/clsync /var/www /home/clsync/bin/ /home/clsync/clsync-rules

  • You're syncing only few files from huge file tree (with a great lot of excludes): clsync -l mirror -p -R -d /dev/shm/clsync -I /home/user /home/clsync/bin/ /home/clsync/clsync-rules

8. Known building issues

  1. Doesn't compiles on old systems

    • In this case you should compile with command "make onoldsystem"

9. Support

To get support, you can contact with me this ways:

10. Developing

I started to write "DEVELOPING" file. You can look there if you wish. ;)

I'll be glad to receive code contribution :)

            -- Dmitry Yu Okunev <> 0x8E30679C

P.S.: Sorry for my English and for the code :)