[systemd-devel] ExecRestart

["Jóhann B. Guðmundsson"]

On 11/29/2012 04:41 AM, Brandon Black wrote:
>
> Hi all,
>
>   I'm trying to write a systemd.service unit file for an existing 
> well-behaved daemon that's used to managing itself.  The daemon binary 
> doubles as its own controller for sysvinit-like command.  For example 
> "foo start" launches a new daemon. "foo stop" stops an existing 
> instance of the daemon.  Similarly for restart, condrestart, status, 
> etc.  This makes things very simple in the world of sysv-like init 
> systems.  The "initscript" just execs the daemon binary and passes on 
> the user action argument, and all of the tricky bits are well-managed 
> within the daemon's own code (pidfiles, sockets, logging, strange 
> corner cases, timing issues, etc).
>
> I can't simply convert the daemon to expect all of systemd's nice 
> features and gut all of its self-management code, as it must still be 
> portable to non-systemd platforms where these features are handy.  For 
> the most part I've been able to successfully work around things, but 
> lack of an ExecRestart is one of my remaining hangups.
>
> I certainly can publish a unit file without this, and restart would be 
> performed by ExecStop -> ExecStart.  However, the daemon has a bunch 
> of nice code to do a better restart than that, and I'd need an 
> ExecRestart to allow users to continue to take advantage of that.
>
> The daemon's "fast restart" code does all of the expensive startup 
> operations in the new daemon first (e.g. parsing large data input), 
> then signals the existing daemon to shut itself down, waits for it to 
> release its critical resources (e.g. sockets, pidfile), and finally 
> takes over those resources and finishes starting itself.  Basically 
> it's using the overlap to avoid long service downtimes during that 
> initial parsing phase (and if that parsing fails, it leaves the old 
> daemon running to boot).
>
> Is there some design reason that we can't have an ExecRestart command? 
>  Successful exit of that command would mean the old instance was 
> killed (which systemd could confirm), and that the restart command has 
> launched a new instance (which systemd can also figure out via PIDFile 
> or guessing/cgroup).  Failure exit of that command would mean the 
> existing daemon instance was left alone (and again, systemd could 
> confirm that state).
>

Which daemon is this ?

JBG