Clean Up Stale nginx Unix Sockets with a systemd Drop-in

When nginx listens on Unix sockets (for example listen unix:/run/nginx-sockets/site.sock; behind a load balancer or another proxy), it normally removes the socket files when it shuts down cleanly. After a crash, a kill -9, or a power loss, the files stay behind, and the next start fails:

nginx: [emerg] bind() to unix:/run/nginx-sockets/site.sock failed (98: Address already in use)

A systemd drop-in can delete stale sockets every time the service starts.

Add the Drop-in

1. Keep nginx's sockets in a directory used only by nginx, such as /run/nginx-sockets, so the cleanup can't touch another service's sockets (PHP-FPM, for example).

2. Create the drop-in with systemctl edit, which opens an editor and saves the file to /etc/systemd/system/nginx.service.d/override.conf:

   systemctl edit nginx

   Add:

   [Service]
   ExecStartPre=/bin/sh -c 'rm -f /run/nginx-sockets/*.sock'

   Or write the file directly:

   mkdir -p /etc/systemd/system/nginx.service.d
   printf '%s\n' '[Service]' "ExecStartPre=/bin/sh -c 'rm -f /run/nginx-sockets/*.sock'" > /etc/systemd/system/nginx.service.d/rm-sock.conf
   systemctl daemon-reload

3. Restart nginx and confirm the drop-in is loaded:

   systemctl restart nginx
   systemctl cat nginx

The command runs through /bin/sh because systemd doesn't expand wildcards like *.sock itself. Drop-in ExecStartPre lines run after the ones in the main unit, so Ubuntu's built-in nginx -t config test still runs first.

Alternative: Let systemd Manage the Directory

If the socket directory lives under /run, systemd can create it at start and delete it, with everything inside, at stop:

[Service]
RuntimeDirectory=nginx-sockets
RuntimeDirectoryMode=0755

systemd removes the directory whenever the service stops, including when it fails or is killed, and /run is cleared on reboot, so stale sockets can't survive. Use this or the ExecStartPre cleanup, not both: RuntimeDirectory deletes the directory on stop, so nothing else should store files in it.