Using systemd units instead of cron

1. Create a systemd unit for acme.sh:

/etc/systemd/system/acme_letsencrypt.service

[Unit]
Description=Renew Let's Encrypt certificates using acme.sh
After=network-online.target

[Service]
Type=oneshot
ExecStart=/path/to/acme.sh <your acme.sh arguments here>

2. Test that it works before creating the timer:

sudo systemctl daemon-reload
sudo systemctl start acme_letsencrypt --now

3. Create systemd timer unit for the service above:

/etc/systemd/system/acme_letsencrypt.timer

[Unit]
Description=Daily renewal of Let's Encrypt's certificates

[Timer]
OnCalendar=daily
RandomizedDelaySec=1h
Persistent=true

[Install]
WantedBy=timers.target

4. Enable timer: sudo systemctl enable acme_letsencrypt.timer