Package tableflip implements zero downtime upgrades. An upgrade spawns a new copy of argv[0] and passes file descriptors of used listening sockets to the new process. The old process exits once the new process signals readiness. Thus new code can use sockets allocated in the old process. This is similar to the approach used by nginx, but as a library. At any point in time there are one or two processes, with at most one of them in non-ready state. A successful upgrade fully replaces all old configuration and code. To use this library with systemd you need to use the PIDFile option in the service file. Then pass /path/to/pid-file to New. You can use systemd-run to test your implementation: systemd-run will print a unit name, which you can use with systemctl to inspect the service. NOTES: Requires at least Go 1.9, since there is a race condition on the pipes used for communication between parent and child. If you're seeing "can't start process: no such file or directory", you're probably using "go run main.go", for graceful reloads to work, you'll need use "go build main.go". Tableflip does not work on Windows, because Windows does not have the mechanisms required to support this method of graceful restarting. It is still possible to include this package in code that runs on Windows, which may be necessary in certain development circumstances, but it will not provide zero downtime upgrades when running on Windows. See the `testing` package for an example of how to use it. This shows how to use the upgrader with the graceful shutdown facilities of net/http. This shows how to use the Upgrader with a listener based service.