Comment by aroch

If you update a central library (e.g. openssl), you'll have to restart in order to deal with in-memory copies being used by other programs. If you're running a Debian server one of the packages to include in your base install is debian-goodies or needrestart because the former bundles a very helpful little script called "checkrestart" and the latter is an updated systemd-compatible version, both of which use `lsof` under the hood to determine when and why package updates require a restart for full effect.