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 nss-lookup.target

[Service]
Type=oneshot
SyslogIdentifier=acme.sh
# --home's argument should be where the acme.sh script resides.
ExecStart=/path/to/acme.sh --cron --home /path/to/acme.sh

2. Disable timestamps (optional):

/path/to/acme.sh/account.conf

NO_TIMESTAMP='1'

3. Test that it works before creating the timer:

sudo systemctl daemon-reload
sudo systemctl start acme_letsencrypt
journalctl -u acme_letsencrypt.service

4. Create systemd timer unit for the service above:

/etc/systemd/system/acme_letsencrypt.timer

[Unit]
Description=Renewal of Let's Encrypt's certificates

[Timer]
OnCalendar=0/6:00:00
RandomizedOffsetSec=6h
FixedRandomDelay=true
Persistent=true

[Install]
WantedBy=timers.target

5. Enable timer:

sudo systemctl start acme_letsencrypt.timer
sudo systemctl enable acme_letsencrypt.timer