Unison is a powerful, open-source file synchronization tool that allows you to keep files and directories consistent across multiple machines. It works efficiently over SSH and is a great alternative to tools like rsync when two-way synchronization is required.
Installing Unison on Debian/Ubuntu
To install Unison, run the following command:
sudo apt update && sudo apt install unison
If you plan to synchronize files over SSH, ensure OpenSSH is installed as well:
sudo apt install openssh-client openssh-server
Setting Up Password-less SSH for Automation
To avoid entering a password every time Unison runs, set up SSH key authentication:
Generate an SSH Key (if you haven’t already):
ssh-keygen -t rsa -b 4096
- Press Enter to save it in the default location (~/.ssh/id_rsa).
- If prompted, enter a passphrase (or leave it blank for no passphrase).
Copy the SSH Key to the Remote Server:
ssh-copy-id mahesh@192.168.1.125
- Enter the password once to install the key.
Verify Password-less SSH Login:
ssh mahesh@192.168.1.125
- You should log in without being asked for a password.
Basic Usage
1. Synchronizing Local Directories
To synchronize two local directories, use:
unison /path/to/source /path/to/destination
unison /home/koha/Dropbox /home/koha/Dcouments
Unison will analyze the differences and prompt you to confirm each action.
2. Synchronizing Over SSH
To sync directories between a local and a remote machine:
unison /home/koha/Dropbox ssh://mahesh@192.168.1.125///home/mahesh/Documents
Replace mahesh@192.168.1.125 with your actual remote server credentials.
3. Using a Profile for Automation
To simplify usage, create a profile in ~/.unison/default.prf:
sudo nano ~/.unison/default.prf
root = /home/koha/Dropbox
root = ssh://mahesh@192.168.1.125///home/mahesh/Documents
auto=true
batch=true
Then run:
unison default
This enables automatic sync without manual confirmation.
Unison is an excellent tool for bidirectional synchronization, providing flexibility and control over file updates. Whether for backups, team collaboration, or server mirroring, it ensures consistency across systems with minimal effort.
