[Bugs] [Bug 1678640] Running 'control-cpu-load.sh' prevents CTDB starting

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1678640



--- Comment #2 from Anoop C S <anoopcs at redhat.com> ---
(In reply to Anoop C S from comment #1)
> (In reply to ryan from comment #0)
> > Actual results:
> > CTDB fails to start with following error:
> > 2019/02/08 20:46:59.612215 ctdbd[2629]: Created PID file
> > /var/run/ctdb/ctdbd.pid
> > 2019/02/08 20:46:59.612267 ctdbd[2629]: Listening to ctdb socket
> > /var/run/ctdb/ctdbd.socket
> > 2019/02/08 20:46:59.612297 ctdbd[2629]: Unable to set scheduler to
> > SCHED_FIFO (Operation not permitted)
> > 2019/02/08 20:46:59.612304 ctdbd[2629]: CTDB daemon shutting down
> 
> Please use the following CTDB setting in /etc/sysconfig/ctdb:
> CTDB_NOSETSCHED=yes
> 
> and try restarting CTDB.

Copy-pasting a summary of the reason for above suggestion from a different bug:

CTDB daemon i.e, ctdbd is a service that by default requests for real-time
scheduling unless it is instructed not to do so via explicit configuration
parameters. By default systemd places all system services into their own
control groups in the "cpu" hierarchy. But the "cpu" cgroup controller of the
kernel demands absolute real-time budget to be explicitly specified. A
reasonable value for required real-time cpu cycles are pre-written into
corresponding configuration files. This value getting overwritten by other
components in the system results in denial of real-time scheduling to services
under this "cpu" hierarchy with error EPERM(Operation not permitted).

ref:
https://www.freedesktop.org/wiki/Software/systemd/MyServiceCantGetRealtime/

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