[systemd-devel] PartOf= Question

[Colin Guthrie]

Hi Steve,

I think I maybe (coincidentally) partly answered some of this question
(or at least outlined the problem) in my other reply on a different
thread made just a moment ago.

Steve Dickson wrote on 12/01/15 19:58:
> Hello,
> 
> The nfs-server service starts both the rpc-mountd service
> and the rpc-idmapd service when the server is started.
> But only brings down the rpc-mountd service when
> the NFS server is stopped. 
> 
> I want nfs-server service to bring both services when
> the server is stopped. 

Do you mean nfs-mountd/idmapd.service here? That's the name I see in
git, but perhaps you've renamed them locally to match their binary
names? (I'm forever mixing up the rpc- vs. nfs- prefixes too FWIW!)

Question: Are idmapd and mountd *only* required for the server? I
thought that idmapd was at least needed for the client too (but this
could easily be a problem with my understanding, so feel free to correct
me).

I'll assume I'm wrong for the sake of argument as you seem to what this
behaviour! :)

> Looking at the difference between rpc-mountd and 
> rpc-idmapd services, I noted the rpc-mountd service
> had:
>    PartOf=nfs-server.service
>    PartOf=nfs-utils.service

I would strongly discourage the use of multiple PartOf= directives.

Note that as the man page describes PartOf is a one-way propagation.
That is if nfs-server is stopped, started or restarted it will propagate
to rpc-mountd.

But likewise is nfs-utils is stopped, started or restarted it too will
propagate, but this might then go out of sync with nfs-server.

In these units, as nfs-mountd is required by nfs-server.service, if
nfs-utils is restarted, then (I think this is correct) nfs-server will
have to go down because it's requirement is no longer true (during the
window when nfs-mountd.service restarting), but there is nothing that
will then start nfs-server again after things are back up.

So by having two PartOf= directives here, issuing "systemctl restart
nfs-utils" when nfs-server is started, will result in nfs-server being
stopped. Now in this particular case, nfs-server is not really a daemon
so things will physically work, but the state will be really confusing
to a sysadmin!


If rpc-mountd and rpc-idmap are essentially bound to nfs-server.service
state, then I would remove both PartOf= lines and simply add a
BindsTo=nfs-server.service line. Forget nfs-utils.service (which I think
should be generally done anyway).

This binds both units state to that of nfs-server.service. If it's
started, they will start, if it is stopped, they will stop. If they are
individually stopped, so will nfs-server (it Requires= them).

They should thus continue to not have any [Install] section.


PartOf is looser than BindTo. It was introduced to allow targets to be
restarted and have all their units restart automatically (often this
would be templated units), but to also allow the individual units that
are part of that target to be restarted individually without affecting
other units in the same target.

Perhaps this is actually what you want here (e.g. to be able to restart
idmap on it's own without having this propagate to the
nfs-server.service too? If so, I believe you should use Wants= in
nfs-server.service rather than Requires= as that way the individual
units can be restarted without actually affecting the state of the
nfs-server itself, but you do have to ensure they are enabled in some
other way (as Wants= will not pull them in automatically).



> and the rpc-idmapd service did not. So I changed 
> the rpc-idmapd.service to:
> 
> [Unit]
> Description=NFSv4 ID-name mapping service
> Requires=var-lib-nfs-rpc_pipefs.mount
> After=var-lib-nfs-rpc_pipefs.mount
> After=network.target
> PartOf=nfs-server.service
> PartOf=nfs-utils.service
> 
> Wants=nfs-config.service
> After=nfs-config.service
> 
> [Service]
> EnvironmentFile=-/run/sysconfig/nfs-utils
> Type=forking
> ExecStart=/usr/sbin/rpc.idmapd $RPCIDMAPDARGS
> 
> which does not work. rpc.idmapd is still running 
> when the nfs-server service is stopped.
> 
> The man page clearly says:
> 
>   When systemd stops or restarts the units listed here, the action
>   is propagated to this unit.
> 
> What am I missing about the PartOf option?


I suspect it's required by something else perhaps? Does it's pid change
(i.e. is it restarted)?

Or dod you just modify the units on disk but forget to run "systemctl
daemon-reload" to reread them?

Col


-- 

Colin Guthrie
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http://colin.guthr.ie/

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