How to synchronize Ubuntu server directories with Unison

Looking to sync directories on two Linux servers in your knowledge center and want to do it on the low-priced? Unison may possibly be just the software you will need.

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You possibly have a handful of Linux servers in your data middle. You also could require to hold specific directories in these servers in sync. For instance, say you have a need to have to retain a /facts listing in sync between individuals servers, so a one application has entry to up-to-date details. Or possibly you just want to keep a synchronized backup of a single server to yet another.

Whatsoever your want, Unison can assist you out. 

Unison is a instrument identical to rsync–the only variation getting that it can monitor and synchronize the two directories, not just just one. The a person caveat to Unison is that it involves you build a passwordless SSH authentication key (in any other case mirroring is not going to do the job), so if this is a deal breaker for you, you can want to pass on this tool. Having said that, if you experience assured in your network safety, (these that a server can use SSH vital authentication with out a password) carry on on.

SEE: 10 issues providers are trying to keep in their very own information centers (TechRepublic download)

What you may have to have

I’m going to reveal utilizing two Ubuntu Servers (each 18.04). You can put in and use Unison on diverse distributions, you only have to modify the set up command, as Unison can be mounted from the typical repositories.

You may also need a person with sudo privileges.

I will be using the subsequent:

  • server1 –
  • server2 –

How to put in Unison

The initial detail to acquire treatment of is the installation of Unison. This must be completed on equally servers. Log in to equally servers and challenge the command:

sudo apt-get install unison unison-all -y

After Unison is set up, you’re ready to keep on.

How to deliver and copy an SSH vital

Now we crank out an SSH critical on server1 only. For this challenge the command:

ssh-keygen -t rsa

When prompted for a password, only strike Enter on your keyboard. 

As soon as the critical is produced, duplicate it to server2 with the command:


With your SSH critical copied, you might be ready to start out employing Unison.

How to use Unison

For screening applications, let us create directories on equally servers. On server1 issue the command:

sudo mkdir -p /facts1

On server2 challenge the command:

sudo mkdir -p /facts2

On both servers, you can want to transform the possession of the new listing–if not Unison is not going to be in a position to publish to it. Alter the ownership to the username who’ll be operating the Unison command like so:

sudo chown -P $Consumer.$Person /facts2

Do the identical on server1 with the command:

sudo chown -P $Consumer.$Consumer /data1

Position a couple of take a look at information in /data1 with the command:

touch /info1/take a look at1,examination2,check3

Now let’s sync the two directories with the command (run on server1):

unison /information1 ssh://192.168..19//data2

For the reason that this is the to start with time you have tried to sync these root folders, you are going to be warned that the synchronization can take some time (it is not going to, mainly because we’ve only included three vacant information to the listing). If this have been a output backup, the initially run could take some time.

Hit Enter on your keyboard to start the procedure. At the time you’ve finished this, you must be prompted to okay the sync of every file. When this is comprehensive, variety y to carry on.

As shortly as you sort y, the sync will manifest. Since we are only syncing the a few new data files, it will transpire very rapid and return you to the bash prompt. To make guaranteed the data files are synced, go to server2 and problem the command:

ls /knowledge2

You must see test1, check2, and take a look at3 outlined (Determine A).

Figure A


Unison has our information now in sync.

How to operate Unison with out interaction

You you should not want to have to reply inquiries every single time you operate Unison, in particular when you’re syncing directories with a good deal of data files. To avert the interaction, challenge the command (on server1):

nano ~/.unison/default.prf

In that configuration file, incorporate the lines:


Preserve and near the file.

Now, when you operate the Unison sync command, you will never be prompted for any enter.

How to build a cron task for Unison

You absolutely really don’t want to have to operate these sync work manually, otherwise you may possibly wind up forgetting and getting out of sync directories in your info center servers. To established this up instantly, you can expect to have to build a cron position on server1. 

1st, let us develop a script to run the sync. Issue the command:

sudo nano /usr/regional/bin/unisonsync

In that file, add the adhering to:

unison /knowledge1 ssh://

Give that new script executable permissions with the command:

sudo chmod ugo+x /usr/area/bin/unisonsync

Produce a cronjob with the command:

crontab -e

In the ensuing file, incorporate the subsequent line (to run the script each and every 5 minutes):

*/5 * * * * /usr/area/bin/unisonsync &> /dev/null

Now you have a file sync system managing that will maintain directories on two of your Linux data center servers in sync every single 5 minutes. Do make sure to examination this by adding data files to the two details directories on equally servers. At the time you are sure the sync is working, you can then established it up on a output device.

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