Reliable Penguin

This Unison program is great. It neatly handles syncing between two servers where changes are occurring on both sides. On one client site it takes about 30 seconds to compare/sync a 23GB /var/www/html/ structure with about 100 sites.

1) Install unison (http://www.cis.upenn.edu/~bcpierce/unison/). Requires "ocaml" compiler (http://caml.inria.fr/), and needs the "etags" command from emacs (so "yum install emacs", whatever)

2) Set up a "/root/.unison/profile-name.prf" file. See example pasted below. Comment out "batch=true" and "silent=true" for initial test runs. Uncomment them for running from a cron job.

3) Run manually to test: unison profile-name

4) If you leave the logging turned on, make an /etc/logrotate.d/unison file, something like this:

/var/log/unison.log {
notifempty
daily
rotate 7
missingok
compress
}


5) Set up cron job(s). Create multiple profiles if specific paths need more frequent syncing. With silent=true, the jobs should produce no output (silent=true automatically sets batch=true).

Sample profile (/root/.unison/profile-name.prf)

# Reasonable defaults
auto=true
confirmbigdeletes=true
contactquietly=true
fastcheck=true
group=true
maxthreads=20
numericids=true
owner=true
times=true

# Dump an archive listing to ~/unison.dump
#dumparchives=true

# Skip confirmation
batch=true

# Suppress output (sets batch=true)
silent=true

# Run in a loop, repeating every X seconds (sort of daemon mode)
#repeat=60

# Log all sync operations
log=true
logfile=/var/log/unison.log

# Backup deleted files
backup=Name *
backuplocation=central
backupdir=/var/www/unison-backups


# Local root
root=/var/www/html/

# Remote root (the double forward-slash between IP and remote path is correct)
root=ssh://1.2.3.4//var/www/html/

# Resolve conflicts in favor of local root
prefer=/var/www/html/


# Limit to specific relative path (can specify multiple path= params)
#path=somepath/

# Don't sync (can specify multiple ignore lines)
ignore=Path */var/cache