systemd drop-in overrides (without editing vendor files)

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One of the most common mistakes when tweaking a service is editing the unit file directly under:

/lib/systemd/system/

That works… until the next package update overwrites your changes.

The clean way is using drop-in overrides.

What is a drop-in override?

It is a file like:

/etc/systemd/system/<unit>.d/override.conf

systemd merges it on top of the original unit.

Create the directory:

sudo mkdir -p /etc/systemd/system/nginx.service.d

Create the override:

sudo tee /etc/systemd/system/nginx.service.d/override.conf >/dev/null <<'EOF'
[Service]
Environment="APP_ENV=prod"
Environment="LOG_LEVEL=info"
EOF

Reload and restart:

sudo systemctl daemon-reload
sudo systemctl restart nginx

Check what systemd is using:

systemctl cat nginx.service

If you need to replace ExecStart, remember you must first clear it:

[Service]
ExecStart=
ExecStart=/usr/sbin/nginx -g "daemon off;"

To debug service errors, journalctl is your friend:

sudo journalctl -u nginx -b -n 200 --no-pager

And if you like small practical posts like this, here’s another one in: Remove multiple files.

Easy peasy! :)