Catch 22 with processes and files

[Bob]

I have a dilemman and need some suggestions. I have a process where I need to send a signal when the configuration file is updated. However, I also have a process (xrdp) where I do not want to update the configuration file if a process is running (Xvnc) so I can restart without interrupting user sessions. So, I think I need:

processes:

files:

processes:

but this is not possible.

Is there a way I can save state between cf-agent runs so the xrdp processes can be restarted at a later time?

[Neil Watson]

There are the three passes, so it may be possible, but we need more of
your requirements.

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Neil H Watson
Sr. Partner, Architecture and Infrastructure
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[Brian Bennett]

I would drop a marker into /tmp then restart if the marker exists and Xvnc is not running.

E.g.:

classes:

  "restart_xrdp_needed" expression => fileexists("/tmp/xrdp_needs_restart");

files:

  "/my/xrdp.config"

    copy_from => secure_cp("/repo/path/xrdp.config","$(sys.policy_hub)"),

    classes => if_repaired("restart_xrdp_needed");

  restart_xrdp_needed::

    "/tmp/xrdp_needs_restart" create => "true";

processes:

  "Xvnc" process_stop => "/usr/bin/false",

    classes => if_notkept("xvnc_is_running");

  !xvnc_is_running.restart_xrdp_needed::

    "xrdp" signals => { "hup" };

I haven't tested running this, so it may not be quite right.

-- 
Brian Bennett
Looking for CFEngine training?
http://www.verticalsysadmin.com/

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[Neil Watson]

You can persist classes between runs. It's neater than a semaphore file.
https://docs.cfengine.com/latest/reference-promise-types-classes.html#persistence

[Brian Bennett]

A persistent class is still a semaphore, just a different kind. The persistence time needs to be long enough to guarantee there will be an interval period where restart is safe, and the class needs to be cancelled/negated after the restart happens.

--
Brian Bennett
Looking for CFEngine training?
http://www.verticalsysadmin.com/

[Neil Watson]

On Mon, Jun 22, 2015 at 09:02:06AM -0700, Brian Bennett wrote:
>A persistent class is still a semaphore, just a different kind.

I said it was neater than a 'semaphore file'. But, yes logically they
are the same. I'm getting out of the pedantic end of the pool now :)