===== Lsyncd =====
Install required libraries:
<code>
apt-get install lsyncd
echo 'fs.inotify.max_user_watches=400000' > /etc/sysctl.d/99-lsyncd.conf
sysctl -p  /etc/sysctl.d/99-lsyncd.conf
</code>

Create the sync directories on both servers:
<code>
mkdir /home/moodle
mkdir /home/moodledata
chmod 775 /home/moodle
chmod 775 /home/moodledata
</code>

Create the user:
<code>
useradd lsyncd
mkdir /home/lsyncd
chown lsyncd:lsyncd /home/lsyncd 
usermod -aG www-data lsyncd
</code>
On server1:
<code>
su - lsyncd
ssh-keygen
</code>
On server2:
<code>
su - lsyncd
mkdir /home/lsyncd/.ssh
chmod 700 /home/lsyncd/.ssh
touch /home/lsyncd/.ssh/authorized_keys
chmod 600 /home/lsyncd/.ssh/authorized_keys
</code>

Copy key from server1 /home/lsyncd/.ssh/id_rsa.pub to server2 /home/lsyncd/.ssh/authorized_keys.

Create Lsyncd configuration on server1:
<code>
touch /etc/lsyncd.conf
touch /etc/lsyncd.exclude
chown lsyncd:lsyncd /etc/lsyncd.conf
chown lsyncd:lsyncd /etc/lsyncd.exclude
touch /var/log/lsyncd.log
touch /var/log/lsyncd-status.log
chown lsyncd:lsyncd /var/log/lsyncd.log
chown lsyncd:lsyncd /var/log/lsyncd-status.log
</code>

Content of /etc/lsyncd.conf:
<code>
settings {
   logfile = "/var/log/lsyncd.log",
   statusFile = "/var/log/lsyncd-status.log",
   statusInterval = 20,
   maxProcesses = 1
}

sync {
   default.rsyncssh,
   source="/home/moodle",
   host="lsyncd@192.168.122.135",
   excludeFrom="/etc/lsyncd.exclude",
   targetdir="/home/moodle",
   rsync = {
     archive = true,
     compress = false,
     whole_file = false
   },
   ssh = {
     port = 22
   }
}
</code>
Create a systemd unit to start automatically with the following name /etc/systemd/system/lsyncd-moodle.service
<code>
[Unit]
Description=Live Syncing (Mirror) Daemon
After=network.target

[Service]
User=lsyncd
Group=lsyncd
Restart=always
Type=simple
Nice=19
ExecStart=/usr/bin/lsyncd -nodaemon -pidfile /run/lsyncd.pid /etc/lsyncd.conf
ExecReload=/bin/kill -HUP $MAINPID
PIDFile=/run/lsyncd.pid

[Install]
WantedBy=multi-user.target
</code>

Reload systemd and enable lsyncd-moodle:
<code>
systemctl daemon-reload
systemctl enable lsyncd-moodle
systemctl start lsyncd-moodle
</code>


==== References ====
  * https://download.moodle.org/download.php/stable404/moodle-4.4.1.tgz
  * https://developers.redhat.com/blog/2018/11/02/how-to-manually-copy-ssh-keys-rhel
  * https://github.com/lsyncd/lsyncd#readme
  * https://docs.rockylinux.org/guides/backup/mirroring_lsyncd/