On Fri, Oct 7, 2022 at 10:24 AM Klaus Ebbe Grue <g...@di.ku.dk> wrote:
> Hi systemd-devel, > > I have a user question which I take the liberty to send here since "about > systemd-devel" says "... it's also OK to direct user questions to this > mailing list ...". > > I have a daemon, /usr/bin/mydaemon, which listens on one and only one TCP > port, say 9999, and which does no more than communicating over 9999 and > creating, reading, writing and deleting files in /home/me/mydaemon/. > > Mydaemon leaves it to systemd to create a socket which listens at 9999. > > It is unimportant whether or not mydaemon is started at boot and it is > also unimportant whether or not mydaemon is socket activated. As long as it > is at least one of the two. > > Now I want to upgrade mydaemon to a new version using a script, without > race conditions and without closing the listening socket. I want the > listening socket to stay open since otherwise there can be a one minute > interval during which it is impossible to reopen 9999. > > If it is just a clean upgrade, the script could replace /usr/bin/mydaemon, > then stop mydaemon. If the daemon is socket activated there is no more to > do. If the daemon is activated only on boot then the script must end up > restarting mydaemon. > > But now I want to do some more while mydaemon is not running. It could be > that my script should take a backup of /home/me/mydaemon/ in case things go > wrong. It could be the script should translate some file in > /home/me/mydaemon/ to some new format required by the new mydaemon or > whatever. > > So I need to stop mydaemon in such a way that mydaemon cannot wake up > while my script fiddles with /home/me/mydaemon/. > Deploy the new version of your daemon to another location (/home/me/mydaemon.new/), perform all processing/conversions that are necessary, *then* stop the socket, `mv mydaemon mydaemon.old`, stop the service, `mv mydaemon.new mydaemon`, start the socket again. The interval for this will be more like half a second than a minute. -- Mantas Mikulėnas
