[slurm-users] License management and invoking scontrol in the prolog

[Davide DelVento]

Hi,

I would like to soft-enforce license utilization only when the -L is
set. My idea: check in the prolog if the license was requested and
only if it were, set the environmental variables needed for the
license.

I looked at all environmental variables set by slurm and did not find
any related to the license as I was hoping.

As a workaround, I could check

scontrol show job $SLURM_JOB_ID | grep License

and that would work, but (as discussed in other messages in this list)
the documentation at https://slurm.schedmd.com/prolog_epilog.html say

> Prolog and Epilog scripts should be designed to be as short as possible
> and should not call Slurm commands (e.g. squeue, scontrol, sacctmgr,
> etc). [...] Slurm commands in these scripts can potentially lead to performance
> issues and should not be used.

This is a bit of a concern, since the prolog would be invoked for
every job on the cluster, and it's a prolog (rather than the epilogue
like discussed in earlier messages).

So two questions:

1) is there a better workaround to check in the prolog if the current
job requested a license and/or
2) would this kind of use of scontrol be okay or is indeed a concern

Thanks!

[Brian Andrus]

Not sure if you can do all the things you intend, but the job_submit
script is precisely where you want to check submission options.

https://slurm.schedmd.com/job_submit_plugins.html

Brian Andrus

[Davide DelVento]

Thanks Brian for the suggestion, which I am now exploring.

The documentation is a bit cryptic for me, but exploring a few things
and checking https://funinit.wordpress.com/2018/06/07/how-to-use-job_submit_lua-with-slurm/
I suspect my slurm install (provided by cluster vendor) was not
compiled with the lua plugin installed. Do you know how to verify if
that is the case or if it's something else? I don't see a way to show
if the plugin is actually being "seen" by slurm, and I suspect it's
not.

Does anyone else have other suggestions or comment on either the
plugin or the prolog workaround?

Thanks!

[Brian Andrus]

I would be surprised if it were compiled without the support. However,
you could check and run something like:

strings /sbin/slurmctld | grep job_submit

(or where ever your slurmctld binary is). There should be quite a few
lines with that in it.

Brian Andrus

[Davide DelVento]

Thanks again, Brian, indeed that grep returns many hits, but none of
them includes lua, i.e.

strings `which slurmctld ` | grep -i job_submit | grep -i lua

returns nothing. So I should use the C rather than the more convenient
lua interface, unless I recompile or am I missing something?

[Brian Andrus]

lua is the language you can use with the job_submit plugin.

I was showing a quick way to see that job_submit capability is indeed in
there.

You can see if lua support is there by looking for the job_submit_lua.so
file is there.
It would be part of the slurm rpm (not the slurm-slurmctl rpm)

Usually it would be found at /usr/lib64/slurm/job_submit_lua.so

If that is there, you should be good with trying out a job_submit lua
script.

Brian Andrus

[Davide DelVento]

Thanks.

I did try a lua script as soon as I got your first email, but that
never worked (yes, I enabled it in slurm.conf and ran "scontrol
reconfigure" after). Slurm simply acted as if there was no job_submit script.

After various tests, all unsuccessful, today I found that link which I
mentioned saying that lua might not be compiled in, hence all my most
recent messages of this thread.

That file is indeed there, so that's good news that I don't need to recompile.
However I'm puzzled on what might be missing...

[Brian Andrus]

Try setting logging to debug mode, then you can get some info from the logs.

Brian Andrus

[Ole Holm Nielsen]

Did you install all prerequiste packages (including lua) on the server
where you built the Slurm packages?

On my system I get:

$ strings `which slurmctld ` | grep HAVE_LUA
HAVE_LUA 1

/Ole

https://wiki.fysik.dtu.dk/niflheim/Slurm_installation#install-prerequisites

[Davide DelVento]

Thanks again to both of you.

I actually did not build Slurm myself, otherwise I'd keep extensive
logs of what I did. Other people did, so I don't know. However, I get
the same grep'ing results as yours.

Looking at the logs reveals some info, but it's cryptic.

[2022-09-06T17:33:56.513] debug3: job_submit/lua:
slurm_lua_loadscript: skipping loading Lua script:
/opt/slurm/job_submit.lua
[2022-09-06T17:33:56.513] error: job_submit/lua:
/opt/slurm/job_submit.lua: [string "slurm.user_msg
(string.format(table.unpack({...})))"]:1: bad argument #2 to 'format'
(no value)

As you can see, there is no line number and there is nothing like
user_msg in this code. There is indeed an "unpack" which is used in
the SchedMD-defined logging helper function which has a comment
"Implicit definition of arg was removed in Lua 5.2" and that's where I
speculate the error occurs.

I should stress, this is with their own example, not my code. I guess
I could forgo the logging and move forward, but that won't probably
lead me very far.

I am contemplating submitting a github issue about it? I did check
that the version of the job_submit.lua I have is the same currently in
the repo at https://github.com/SchedMD/slurm/blob/master/etc/job_submit.lua.example

[Ole Holm Nielsen]

Hi Davide,

I suggest that you check your job_submit.lua script with the LUA compiler:

luac -p /etc/slurm/job_submit.lua

I have written some more details in my Wiki page
https://wiki.fysik.dtu.dk/niflheim/Slurm_configuration#job-submit-plugins

Best regards,
Ole

[Davide DelVento]

Thanks Ole, your wiki page sheds some light on this mystery.
Very frustrating that even the simple example provided in the release
fails, and it fails at the most basic logging functionality.

Note that "my" job_submit.lua is now the unmodified, slurm-provided
one.... and that the luac command returns nothing in my case (this is
Lua 5.3.4) so syntax seems correct?

Yet the logs report the problem I mentioned rather than the actual
content that the plugin is attempting to log.

On Wed, Sep 7, 2022 at 2:13 AM Ole Holm Nielsen

[Brian Andrus]

Possibly way off base, but did you happen to do any of the editing in
Windows? Maybe running into the cr/lf issue for how windows saves text
files?

Brian Andrus

[Davide DelVento]

No, I never moved that file from the Linux cluster (and I do the
editing with VIM which warns me of that possible issue).

[Ole Holm Nielsen]

Hi Davide,

In your slurmctld log you see an entry "error: job_submit/lua:
/opt/slurm/job_submit.lua".

What I think happens is that when slurmctld encounters an error in
job_submit.lua, it will revert to the last known good script cached by
slurmctld and ignore the file on disk from now on, even if it has been
corrected. An "scontrol reconfig" may make slurmctld reread the
job_submit.lua, please try it.

I believe that this slurmctld behavior is undocumented at present. Please
see https://bugs.schedmd.com/show_bug.cgi?id=14472#c15 for a description:

> And, if after the reconfigure, the job_submit.lua is wrong formatted (or missing), it will use the previous version of the script (which we have stored backup previously):

/Ole

[Davide DelVento]

Thanks Ole, for this clarification, this is very good to know.

However, the problem is that the very example provided by slurm itself
is the one that has the error. I removed the unpack part with the
variable arguments and that fixed that part.

Unfortunately, the job_desc table is always empty so the whole
job_submit.lua seems like a moot point? Or the example is so outdated
(given that it cannot even log correctly) that this is now performed
in a different way??
Davide

On Thu, Sep 8, 2022 at 12:23 AM Ole Holm Nielsen

[Davide DelVento]

For other poor souls coming to this conversation, here is the conclusion.

$ sbatch --version
slurm 21.08.5

$ # irrelevant parts omitted from copy-paste for brevity
$ cat /opt/slurm/job_submit.lua
log_prefix = 'slurm_job_submit'
function slurm_job_submit(job_desc, part_list, submit_uid)
slurm.log_info("LOOPING")
for key, value in pairs(job_desc) do
slurm.log_info("%s: key=%s value=%s", log_prefix, key, value)
end
slurm.log_info("END LOOPING")
slurm.log_info("%s: user %s(%u) job_name=%s", log_prefix,
job_desc.user_name, submit_uid, job_desc.name)
return slurm.SUCCESS
end

$ sudo tail /var/log/slurm/slurmctld.log
[2022-09-12T08:13:16.310] _slurm_rpc_submit_batch_job: JobId=16028
InitPrio=4294887729 usec=198
[2022-09-12T08:13:17.213] sched: Allocate JobId=16028
NodeList=co49svnode13 #CPUs=16 Partition=compute512
[2022-09-12T08:15:01.090] lua: LOOPING
[2022-09-12T08:15:01.090] lua: END LOOPING
[2022-09-12T08:15:01.090] lua: slurm_job_submit: user
ddvento(57002254) job_name=lic.slurm
[2022-09-12T08:15:01.091] _slurm_rpc_submit_batch_job: JobId=16029
InitPrio=4294887728 usec=204
[2022-09-12T08:15:01.289] sched/backfill: _start_job: Started
JobId=16029 in compute512 on co49svnode14
[2022-09-12T08:15:17.330] _job_complete: JobId=16028 WEXITSTATUS 0
[2022-09-12T08:15:17.330] _job_complete: JobId=16028 done

Note how the looping is ended. This is probably just my naiveness and
ignorance with how lua work.

In conclusion, I am now able to see job_desc.licenses for example with:

slurm.log_info("%s: licenses=%s", log_prefix, job_desc.licenses)

So now I need to just implement my logic.

Thank you everybody in this conversation for helping to sort out this
issue. Greatly appreciated!