I needed a way to mirror a directory between to shared nothing servers.  I started out uing cron to fire off rsync, but the application required the files be synched "immediately".

Enter inotify.  I installed the inototify-tools go get a shell interface to filesystem events from the kernal.  A couple lines of shell script later and we have a daemon like utility which waits for relevant events and rsyncs the required minimum files.

Run like so:

nohup sync.sh /full/path/to/dir user@host & > /dev/null 2>&1

After I wrote this I found a couple other scripts and programs which do the same or similar things, but this one is pretty minimal and I like that.

• http://code.google.com/p/lsyncd/
• http://ebalaskas.gr/blog/?page=PIrsyncD
• http://www.linuxawy.org/node/13

#!/bin/sh

set -e
set -u

BASEDIR="$1"
REMOTE_HOST="$2"
RSYNC="rsync -av -e ssh --delete "

# Initial sync
$RSYNC ${BASEDIR}/* ${REMOTE_HOST}:${BASEDIR}/

# Wait for individual file events and keep in sync
inotifywait --format '%e %w' -e close_write -e move -e create -e delete -qmr $BASEDIR | while read EVENT DIR
do
  # Fork off rsync proc to do sync
  $RSYNC ${DIR}/* ${REMOTE_HOST}:${DIR}/ &
done