mirror of https://github.com/octoleo/lsyncd.git
122 lines
4.8 KiB
Plaintext
122 lines
4.8 KiB
Plaintext
lsyncd - Live Syncing (Mirror) Daemon
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DESCRIPTION:
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Lsyncd uses rsync to synchronize local directories with a remote machine
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running rsyncd. Lsyncd watches multiple directories trees through inotify.
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The first step after adding the watches is to, rsync all directories with
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the remote host, and then sync single file buy collecting the inotify events.
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So lsyncd is a light-weight live mirror solution that should be easy to
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install and use while blending well with your system.
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See lsyncd --help for detailed command line options.
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WHEN TO USE:
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Lsyncd is designed to synchronize a local directory tree with low profile of
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expected changes to a remote mirror. On the receivers side rsyncd can be
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configured to also change the uid/gid of the file. Lsyncd is especially
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useful to sync data from a secure area to a not-so-secure area (e.g. as a
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one way connection to allow employees to publish their files to a public
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accessible web server).
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WHEN NOT TO USE:
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* File with active file handles (e.g. database files)
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* Directories where many changes occur (like mail or news servers)
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In these cases e.g. DRBD (see http://www.linux-ha.org/DRBD) might be better
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for you.
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COMPARISONS:
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Lsyncd vs. DRBD:
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DRBD operates on block device level. This makes it useful for
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synchronizing systems that are under heavy load. Lsyncd on the other hand
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* does not require you to change block devices and/or mount points.
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* allows you to change uid/gid of the transferred files.
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* separates the receiver through the one-way nature of rsync.
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However when using lsyncd a file change can possibly result in a full file
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transfer (at least for binary files) and is therefore unsuitable for
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databases. Also a directory rename will result in transferring the whole
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directory.
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Lsyncd vs. incron:
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Incron does not (yet) support recursive directory watching making it
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unsuitable for described needs (http://inotify.aiken.cz/?section=incron&page=about&lang=en).
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In fact a different approach would have been to extent incron. However, we
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decided to stick to the NIH principle (Not Invented Here) :-), because extending
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the C++ solution seemed to tedious.
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Lsyncd vs. FUSE:
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This is another interesting idea is to write a daemon that provides a
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shadow file system through fuse. When accessing a file the data is synced
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to local file as well as the remote file. Whit this approach inotify could
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be replaced. BindFS (see http://www.cs.helsinki.fi/u/partel/bindfs/)
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does this for local mirroring. We discarded this idea because it would
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affect performance of normal operations in a negative way.
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Lsyncd vs. cron:
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If you find a solution using cron to call rsync over the whole directory
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tree periodically after every 'X' hours/minutes/seconds more satisfying
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than lsyncd, please go for it *sulking*. We don't like it!
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LSYNCD USAGE EXAMPLES:
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/usr/sbin/lsyncd /var/www/ remotehost::wwwshare/
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This watches and rsycn's the local directory /var/www/ with all
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subdirectories and transfers them to 'remotehost' using the rsync-share
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'wwwshare'.
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/usr/sbin/lsyncd --nodaemon --exclude-from /etc/lsycnd/exclude \
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/var/www/ remotehost::wwwshare/
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This will also rsync/watch '/var/www', but it excludes files and directories
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from '/etc/lsycnd/exclude'. Additionally this example lsyncd will not fork,
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and log to stdout/stderr instead.
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/usr/sbin/lsyncd %userwww remotehost::wwwshare/foobar/
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This special target will scan through all directories in /home and syncs all
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www subdirectories of the users to wwwshare in the subdirectory foobar.
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The user peter having his local data in /home/peter/www/ will have it
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rsynced to ::wwwshare/foobar/peter/.
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LIMITATIONS:
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Be aware that the kernel limits the number of watches. You can see the limit
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in
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/proc/sys/fs/inotify/max_user_watches
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which is usually set to 8192. This means lsyncd cannot watch more than 8192
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directories unless you change the kernel setting. Lsyncd itself has no
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limits.
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Because Axel is lazy the maximum possible size a filename is 8192. If you
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need more, change MAX_PATH in lsyncd.c. Or send me patches that introduce
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dynamic memory usage.
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SOURCE DOCUMENTATION:
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The only file of interest is 'lsyncd.c' which includes comments.
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Everything else in the tarball is packaging bushwa.
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DISCLAIMER:
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Besides the usual disclaimer in the license, we want to specifically EMPHASIZE
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that NEITHER the authors NOR any organization the authors are associated with
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can and will hold responsible for data-loss caused by possible malfunctions
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of lsyncd. Especially if you run it with root privileges ;-) (we ourselves
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run lsyncd as www-data).
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FEEDBACK:
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Please send praises and feedback to: axel.kittenberger@univie.ac.at
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