How to Use Rsync with SSH Keys

This tutorial teaches you how to sync files between two Ubuntu 22.04 desktop machines using rsync with SSH keys.

Requirements

Although most Linux distros have both tools installed, some new versions may lack them. So, the first step toward using rsync with SSH keys is installing rsync on Ubuntu. Next, you should install the OpenSSH server and configure it as follows.

Update and upgrade packages before the installation.

sudo apt update
sudo apt upgrade

Install the OpenSSH server.

sudo apt install openssh-server

Enable SSH service.

sudo systemctl enable ssh

Start the service.

sudo systemctl start ssh

Confirm whether the service is running.

sudo systemctl status ssh

Configure firewall, allowing SSH to run on port 22.

sudo ufw allow ssh
sudo ufw enable
sudo ufw status

Connect the Two machines Is the remote machine reachable?

After installing rsync and SSH server, the next step is to ensure the remote machine is reachable. We can use the ping command for that purpose.

Input

ping [hostname or ip address]

e.g.

ping 192.168.56.107

Output

PING 192.168.56.107 (192.168.56.107) 56(84) bytes of data.
64 bytes from 192.168.56.107: icmp_seq=1 ttl=64 time=1.03 ms
64 bytes from 192.168.56.107: icmp_seq=2 ttl=64 time=0.847 ms
64 bytes from 192.168.56.107: icmp_seq=3 ttl=64 time=0.641 ms
64 bytes from 192.168.56.107: icmp_seq=4 ttl=64 time=0.904 ms
64 bytes from 192.168.56.107: icmp_seq=5 ttl=64 time=1.10 ms
^C
--- 192.168.56.107 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4100ms
rtt min/avg/max/mdev = 0.641/0.903/1.096/0.158 ms

The system receives packets from the remote machine. Since the two machines communicate, let’s try logging into the remote machine.

Generate SSH keys

Generate SSH keys on the local machine using the ssh-keygen command.

ssh-keygen -t rsa -b 4096

-t is the SSH key type, while -b denotes the number of bits.

Answer prompts till the key pairs are generated. On checking the keys,

Input

ls ~/.ssh/

We find two pairs: public and private keys.

Output

id_rsa id_rsa.pub known_hosts

Let’s copy the public key (ending in .pub) to the remote machine. Before that, let’s create the destination directory and file.

Store the public keys remotely

Log into the remote machine using a password.

ssh [username]@[hostname or ip address]

e.g.

ssh [email protected]

Create a .ssh directory and an authorized_keys file inside it.

mkdir ~/.ssh
touch ~/.ssh/authorized_keys

Next, log out of the remote machine.

exit

And return to the local machine before sending the public key to the remote machine’s ~/.ssh/authorized_keys file.

scp ~/.ssh/id_rsa.pub [email protected]:/home/user/.ssh/authorized_keys

Now try logging in without a password.

Log in with SSH Keys

ssh [user]@[ip address]

e.g.

ssh [email protected]

And voila, we are logged into the remote machine without retyping the password!

Now that we can log into the remote machine, let’s start syncing files across the two machines.

Lab Environment Setup

This section creates an environment to transfer

• files only,
• files and directories recursively, and
• all files and directories with their ownership, timestamps and modification details.

Let’s start by creating the local files and directories.

Host Machine

mkdir originalDirectory localDir1 localDir2 localDir3 localDir4
cd originalDirectory
touch originalFile1 originalFile2
mkdir originSubDirectory && cd originSubDirectory
touch originSubFile

Then, repeat the procedure in the remote machine but with different file and directory names.

First, SSH into the remote machine.

ssh [username]@[hostname or ip address]

e.g.

ssh [email protected]

Remote Machine

mkdir remoteDir destinationDirectory1 destinationDirectory2 destinationDirectory3 destinationDirectory4
cd remoteDir
touch remoteFile1 remoteFile2
mkdir remoteSubDirectory && cd remoteSubDirectory
touch remoteFile3

Lastly, return to the local machine’s home directory.

exit
cd

That’s all we need to start syncing files.

Examples

This section illustrates how to sync files and directories across machines using the following rsync options:

• -a: sync all file details, including timestamps, modifications, users and groups.
• -n: run the command but don’t make changes,
• -P: show the progress of the sync process.
• -r: recursive file/directory sync.
• -z: compress large data during transfer and decompress it at the destination.

Example 1: Sync Files Only A. From Local to Remote Machine sync regular files only

rsync originalDirectory/* [email protected]:destinationDirectory1

Output

skipping directory originSubDirectory

Log into the remote machine and verify the file transfer

ssh [email protected]
ls destinationDirectory1

Output

originalFile1 originalFile2

The system skipped directories and transferred only regular files: originalFile1 and originalFile2. Let’s repeat the above process, but instead transfer files from the remote machine to the local one.

B. From Remote to Local Machine sync files

rsync us[email protected]:remoteDir/* localDir1

check files

ls localDir1

Output

remoteFile1 remoteFile2

Likewise, only regular files, remoteFile1 and remoteFile2, were synced.

Example 2: Sync Files and Folders Recursively A. From Local to Remote Machine (a) before sync

ssh [email protected]
ls -l destinationDirectory2

(b) sync

rsync -rzP originalDirectory/ [email protected]:destinationDirectory2

(c) after sync

sh [email protected]
ls -l destinationDirectory2

Output

[email protected]:~$ ssh [email protected]
Welcome to Ubuntu 22.04.1 LTS (GNU/Linux 5.15.0-46-generic x86_64)

* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage

0 updates can be applied immediately.

9 updates could not be installed automatically. For more details,
see /var/log/unattended-upgrades/unattended-upgrades.log
Last login: Thu Aug 25 15:06:57 2022 from 192.168.56.108
[email protected]:~$ ls -l destinationDirectory2
total 0
[email protected]:~$ exit
logout
Connection to 192.168.56.107 closed.
[email protected]:~$ rsync -rzP originalDirectory/ [email protected]:destinationDirectory2
sending incremental file list
originalFile1
0 100% 0.00kB/s 0:00:00 (xfr#1, to-chk=3/5)
originalFile2
0 100% 0.00kB/s 0:00:00 (xfr#2, to-chk=2/5)
originSubDirectory/
originSubDirectory/originSubFile
0 100% 0.00kB/s 0:00:00 (xfr#3, to-chk=0/5)
[email protected]:~$ ssh [email protected]
Welcome to Ubuntu 22.04.1 LTS (GNU/Linux 5.15.0-46-generic x86_64)

* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage

0 updates can be applied immediately.

9 updates could not be installed automatically. For more details,
see /var/log/unattended-upgrades/unattended-upgrades.log

Last login: Thu Aug 25 15:07:22 2022 from 192.168.56.108
[email protected]:~$ ls -l destinationDirectory2
total 4
-rw-rw-r-- 1 user user 0 Hag 25 15:08 originalFile1
-rw-rw-r-- 1 user user 0 Hag 25 15:08 originalFile2
drwxrwxr-x 2 user user 4096 Hag 25 15:08 originSubDirectory

B. From Remote to Local Machine Input

exit
ls -l localDir3
rsync -rvn [email protected]:remoteDir/ localDir3
rsync -rv [email protected]:remoteDir/ localDir3
ls -l localDir3

Output

[email protected]:~$ exit
logout
Connection to 192.168.56.107 closed.
[email protected]:~$ ls -l localDir3
total 0
[email protected]:~$ rsync -rvn [email protected]:remoteDir/ localDir3
receiving incremental file list
remoteFile1
remoteFile2
remoteSubDirectory/
remoteSubDirectory/remoteFile3

sent 37 bytes received 163 bytes 400.00 bytes/sec
total size is 0 speedup is 0.00 (DRY RUN)
[email protected]:~$ rsync -rv [email protected]:remoteDir/ localDir3
receiving incremental file list
remoteFile1
remoteFile2
remoteSubDirectory/
remoteSubDirectory/remoteFile3

sent 93 bytes received 279 bytes 248.00 bytes/sec
total size is 0 speedup is 0.00
[email protected]:~$ ls -l localDir3
total 4
-rw-rw-r-- 1 user user 0 Hag 25 15:22 remoteFile1
-rw-rw-r-- 1 user user 0 Hag 25 15:22 remoteFile2
drwxrwxr-x 2 user user 4096 Hag 25 15:22 remoteSubDirectory

Example 3: Sync Entire Directory with Its Configurations A. From Local to Remote Machine Input

rsync -av originalDirectory/ [email protected]:destinationDirectory3

Output

[email protected]:~$ rsync -av originalDirectory/ [email protected]:destinationDirectory3
sending incremental file list
./
originalFile1
originalFile2
originSubDirectory/
originSubDirectory/originSubFile

sent 308 bytes received 84 bytes 261.33 bytes/sec
total size is 0 speedup is 0.00

B. From Remote to Local Machine Input

rsync -azP [email protected]:remoteDir/ localDir3/

Output

[email protected]:~$ rsync -azP [email protected]:remoteDir/ localDir3/
receiving incremental file list
./
remoteFile1
0 100% 0.00kB/s 0:00:00 (xfr#1, to-chk=3/5)
remoteFile2
0 100% 0.00kB/s 0:00:00 (xfr#2, to-chk=2/5)
remoteSubDirectory/
remoteSubDirectory/remoteFile3
0 100% 0.00kB/s 0:00:00 (xfr#3, to-chk=0/5)

Summary

This tutorial taught you how to sync files between a local machine and a remote one.

It walked you through configuring an open SSH server locally, generating SSH keys, and transferring the public key to a remote machine using the scp command. Next, you learned how to sync files using rsync options like -a, -v, -n, -z, -r, and -P. Lastly, you learned how to verify a successful file transfer.