Keeping directories in sync with unison
As opposed to rsync, unison is a two way file synchronizer. Similar to MySQL’s master to master replication. To set it up in Ubuntu (Intrepid) keep on reading…
1. Install unison on both servers
apt-get install unison
2. Create a script to add to crontab to call unison periodically
unison -numericids -owner -silent -times -contactquietly -batch -auto -log -logfile /var/log/unison.log profile_file 2>&1
3. Create the above mentioned profile file on ~/.unison/profile_file.prf
root = ssh://server_ip//path/to/root/dir root = /path/to/root/dir ignore = Regex .*(cache|Cache|te?mp|logs?).* # ignore log and cache files
That’s it! Now add the following line to your crontab to execute it every 5min
*/5 * * * * /path/to/my_unison_script.sh
After a few days of running this I found that sometimes one unison execution would overlap another. To resolve this I found a little tool called lockrun
To get it to work I did:
1. Download the source code from the official lockrun website
wget http://unixwiz.net/tools/lockrun.c
2. Build/install as shown in http://unixwiz.net/tools/lockrun.html
gcc lockrun.c -o lockrun sudo cp lockrun /usr/local/bin/
3. Change the previous crontab line to use lockrun
*/5 * * * * /usr/local/bin/lockrun --lockfile=/tmp/hosting.lockrun -- /path/to/my_unison_script.sh
All done!!!
Thanks for article. Everytime like to read you.
I had this running nicely as it was from the command line, but saw /var/log/unison.log that it was bombing out when run from crontab with the following error:
Sys_error(“Broken pipe”)
My fix was to use nohup in the crontab:
[code]
*/5 * * * * nohup /usr/local/bin/lockrun --lockfile=/tmp/hosting.lockrun -- /root/bin/my_unison_script.sh > /dev/null 2>&1
[/code]
This seems to have done the trick.
I also recommend considering having “CONFLICT” resolution in the profile.
e.g. When both ends have been modified, prefer the local copy.
[code]
# Resolve conflicts in favor of local root
prefer=/path/to/root/dir
[/code]
In particular this is good when you are sync-ing two directories which have already been duplicated. Unison makes a big song and dance of flagging all of the files as “CONFLICTS” in the log, which gets very large, if you don’t start with a master at only one end.
Alternatively, be sure to start with an empty directory at one end and then the conflicts will be genuine issues.
A big thanks for this article pablo, it is a great way to get started!