Setup Unison in CentOS 7

Unison is one of the utilities that is used to replicate files between servers. A big advantage of Unison is its support for master-master replication.

Until recently, Unison was available in the Epel repository, but for unknown reasons it is no longer there, so it is suggested to compile it from the source.

Prepare first:

yum install ocaml ocaml-camlp4-devel ctags ctags-etags

Download and make Unison:

cd /usr/src  
wget http://www.seas.upenn.edu/~bcpierce/unison//download/releases/stable/unison-2.48.4.tar.gz  
tar xvfz unison-2.48.4.tar.gz  
cd src  
make

sudo cp -v unison /usr/local/sbin/  
sudo cp -v unison /usr/bin

You got to do the steps above to copy the binary into one of the $PATH folders to avoid the following error:

Contacting server ...
bash: unison: command not found  
Fatal error: Lost connection with the server

Create configuration folder:

mkdir ~/.unison/  
cd ~/.unison/

Create configuration file to sync with server web2:

vim sync-web2.prf

File contents:

# Reasonable defaults
auto=true
confirmbigdeletes=true
contactquietly=true
group=true
maxthreads=20
numericids=true
owner=true
times=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/
maxbackups=2

# Local root
root=/var/www/vhosts/website_name/

# Remote root (the double forward-slash between IP and remote path is correct)
root=ssh://web2_ip_address/var/www/vhosts/website_name/

# Resolve conflicts in favor of local root
prefer=newer

# Don't sync (can specify multiple ignore lines)
#ignore=Path */var/cache
ignore=Path anon_ftp
ignore=Path bin
ignore=Path conf
ignore=Path error_docs
ignore=Path httpsdocs
ignore=Path statistics
ignore=Path subdomains
ignore=Path web_users
ignore=Path tmp/session
ignore=Path tmp/cache    
ignore=Path tmp/page_parse_time.log
ignore=Path tmp/sessionsadmin
ignore=Path rewrite.log

You got to customize the following values:

• Local root
• Remote root

Run the following to sync:

unison sync-web2

Create cron task to run the sync periodically (every 10 minutes)

crontab -e  
*/10 * * * * unison sync-web2 2>&1 > /dev/null

or even more often (every minute):

* * * * * unison sync-web2 2>&1 > /dev/null

https://www.digitalocean.com/community/questions/install-unison-in-centos-7