May 2026 - slurm-users - lists.schedmd.com

Nodes Become Invalid Due to Less Total RAM Than Expected
by Xaver Stiensmeier 10 Aug '26

10 Aug '26

Dear slurm-user list, in the past we had a bigger buffer between RealMemory <https://slurm.schedmd.com/slurm.conf.html#OPT_RealMemory> and the instance memory. We then discovered that the right way is to activating the *memory option* (SelectTypeParameters=CR_Core_Memory) and setting MemSpecLimit <https://slurm.schedmd.com/slurm.conf.html#OPT_MemSpecLimit> to secure RAM for system processes. However, now we run into the problem that due to *on demand scheduling*, we have to setup the slurm.conf in advance by using the RAM values from our flavors as reported by our cloud provider (OpenStack). These RAM values are higher than the RAM values the machines actually have later on: ram_in_mib by openstack total_ram_in_mib by top/slurm 2048 1968 16384 15991 32768 32093 65536 64297 122880 120749 245760 241608 491520 483528 Given that we have to define the slurm.conf in advance, we kinda have to predict how much total ram the instances have once created. Of course I used linear regression to approximate the total ram and then lowered it a bit to have some cushion, but this feels unsafe given that future flavors could differ from that. From the kernel documentation <https://www.kernel.org/doc/Documentation/filesystems/proc.txt> I know that MemTotal is MemTotal: Total usable ram (i.e. physical ram minus a few reserved bits and the kernel binary code) but given that the concrete reserved bits are quite complex <https://witekio.com/blog/cat-proc-meminfo-memtotal/>, I am wondering whether I am doing something wrong as this issue doesn't feel niche enough to be that complicated. --- Anyway, setting the RAM value in the slurm.conf above total ram by predicting too much, leads to errors and nodes being marked as invalid: [2025-08-11T08:19:04.736] debug: Node NODE_NAME has low real_memory size (241607 / 245760) < 100.00% [2025-08-11T08:19:04.736] error: _slurm_rpc_node_registration node=NODE_NAME: Invalid argument or |[2025-07-03T12:57:18.486] error: Setting node NODE_NAME state to INVAL with reason:Low RealMemory (reported:64295 < 100.00% of configured:68719)| |Any hint on how to solve this is much appreciated! | Best regards, Xaver

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slurmctld keeps segfaulting, possibly during or just after backfill
by Marcus Lauer 21 Jun '26

21 Jun '26

We are running into a problem where slurmctld is segfaulting a few times a day. We had this problem with SLURM 23.11.8 and now with 23.11.10 as well, though the problem only appears on one of the several SLURM clusters we have, and all of them use one of those versions of SLURM. I was wondering if anyone has encountered a similar issue and has any thoughts on how to prevent this. Obviously we use "SchedulerType=sched/backfill" but strangely when I switched to sched/builtin for a while there were still slurmctld segfaults. We also set "SchedulerParameters=enable_user_top,bf_max_job_test=2000". I have tried turning those off but it did not help. I have also tried tweaking several other settings to no avail. Most of the cluster runs Rocky Linux 8.10 (including the slurmctld system) though we still have some Scientific Linux 7.9 compute nodes (we compile SLURM separately for those). Here is the crash-time error from journalctl: Oct 02 06:31:20 our.host.name kernel: sched_agent[2048355]: segfault at 8 ip 00007fec755d7ea8 sp 00007fec6bffe7e8 error 4 in libslurmfull.so[7fec7555a000+1f4000] Oct 02 06:31:20 our.host.name kernel: Code: 48 39 c1 7e 19 48 c1 f8 06 ba 01 00 00 00 48 d3 e2 48 f7 da 48 0b 54 c6 10 48 21 54 c7 10 c3 b8 00 00 00 00 eb da 48 8b 4f 08 <48> 39 4e 08 48 0f 4e 4e 08 49 89 c9 48 83 f9 3f 76 4e ba 40 00 00 Oct 02 06:31:20 our.host.name systemd[1]: Started Process Core Dump (PID 2169426/UID 0). Oct 02 06:31:20 our.host.name systemd-coredump[2169427]: Process 2048344 ( slurmctld) of user 991 dumped core. This is followed by a list of each of the dozen or so related threads. The one which is dumping core is first and looks like this: Stack trace of thread 2048355: #0 0x00007fec755d7ea8 bit_and_not (libslurmfull.so) #1 0x000000000044531f _job_alloc (slurmctld) #2 0x000000000044576b _job_alloc_whole_node_internal (slurmctld) #3 0x0000000000446e6d gres_ctld_job_alloc_whole_node (slurmctld) #4 0x00007fec722e29b8 job_res_add_job (select_cons_tres.so) #5 0x00007fec722f7c32 select_p_select_nodeinfo_set (select_cons_tres.so) #6 0x00007fec756e7dc7 select_g_select_nodeinfo_set (libslurmfull.so) #7 0x0000000000496eb3 select_nodes (slurmctld) #8 0x0000000000480826 _schedule (slurmctld) #9 0x00007fec753421ca start_thread (libpthread.so.0) #10 0x00007fec745f78d3 __clone (libc.so.6) I have run slurmctld with "debug5" level logging and it appears that the error occurs right after backfill considers a large number of jobs. Slurmctld could be failing at the end of backfill or when doing something which happens just after backfill runs. Usually this is the last message before the crash: [2024-09-25T18:39:42.076] slurmscriptd: debug: _slurmscriptd_mainloop: finished If anyone has any thoughts or advice on this that would be appreciated. Thank you. -- Marcus Lauer Systems Administrator CETS Group, Research Support

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How to weight nodes properly based on RAM to prevent small instances clogging big instances with backfilling
by Xaver Stiensmeier 15 Jun '26

15 Jun '26

Dearl Slurm User List, I am currently reviewing a slurm.conf where the developer set Weight manually to attribute a greater weight to machines that have more RAM to force smaller jobs on smaller instances. However, I feel like there is something already in place or better than manually setting the weights, but I couldn't find it. If I understand correctly Slurm does not schedule jobs to the smallest possible node on default. So small jobs can be scheduled to large instances and a big job might have to wait indefinitely when using backfilling. I thought that Slurm does have mechanisms to prevent this but was unable to find it again in the documentation. Is there really no automatism at place or am I overlooking something? Best, Xaver

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Purging of job_script and job_env from the database in 26.05
by Ole Holm Nielsen 01 Jun '26

01 Jun '26

If you are using AccountingStoreFlags=job_script and/or job_env in slurm.conf to store job scripts in the Slurm database, you may be interested in a highly useful feature introduced in Slurm 26.05: Previously, the stored job_scripts and job_env entries would accumulate without bounds in the database, potentially causing database performance or size issues, especially while upgrading Slurm. With 26.05 there are some new slurmdbd.conf options which can be used to purge job_script or job_env entries in the database, see ticket_23818 [1]. This new feature isn't mentioned at all in the Release notes [4], and is only inconspicuously mentioned way down in the Changes section [3] as: > Adding new archive/purge options to allow for explicit archiving of job_scripts and job_env without jobs. The safe way to enable the new purge parameters is to introduce them very gradually, for example: PurgeJobScriptAfter=2000days PurgeJobEnvAfter=2000days and lower the values little by little over time (restarting slurmdbd each time). The MaxPurgeLimit [5] parameter may alternatively be used to limit the amount of database work. Best regards, Ole [1] https://support.schedmd.com/show_bug.cgi?id=23818 [2] https://slurm.schedmd.com/slurm.conf.html#OPT_AccountingStoreFlags [3] https://github.com/SchedMD/slurm/releases [4] https://slurm.schedmd.com/release_notes.html [5] https://slurm.schedmd.com/slurmdbd.conf.html#OPT_MaxPurgeLimit -- Ole Holm Nielsen PhD, Senior HPC Officer Department of Physics, Technical University of Denmark

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Large overhead for --task-epilog
by Alan O'Cais 29 May '26

29 May '26

Hi all, I've been experimenting with task prolog/epilog and noticed that task epilogs have significant overhead. The overhead seems to be independent of the epilog script content: $ cat test.sh #!/bin/bash $ time srun --overlap --task-prolog=$PWD/test.sh --ntasks=64 sleep 1 real 0m1.730s user 0m0.211s sys 0m0.009s $ time srun --overlap --task-prolog=$PWD/test.sh --task-epilog=$PWD/test.sh --ntasks=2 sleep 1 real 0m3.530s user 0m0.213s sys 0m0.007s $ time srun --overlap --task-prolog=$PWD/test.sh --task-epilog=$PWD/test.sh --ntasks=64 sleep 1 real 1m5.936s user 0m0.216s sys 0m0.005s This test was on one node, with 64 tasks in the allocation. The overhead seems linked only to number of tasks per node, as adding additional nodes did not increase the overhead. I saw this on $ srun --version slurm 23.11.10-BullSequana.1.2.1 and someone else reproduced similar results with |slurm 25.05.7|. I can live with the overhead, but I am curious as to why it happens and to understand the design of the implementation. Does the task epilog script only run when all tasks finish, or does it run immediately at exit for each task? Are the calls serialised? My use case is a fusermount that I want to mount in userspace at task start and clean up at task finish, one task per node is responsible for the mount/unmount and I want to understand if I have a race condition for the unmount. Any advice very much appreciated, Alan

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Technical Update: Native Slurm Simulation Environment Successfully Configured
by sami sami 28 May '26

28 May '26

Hi All, I am currently working on a single Linux machine running *Ubuntu 25.10* and am looking to conduct performance testing on the *Slurm backfill algorithm*. My objective is to simulate a cluster environment consisting of *1,024 nodes*. While researching existing solutions, I found that many modern Slurm-simulator implementations (such as various plugin-based designs) rely heavily on *Docker and Docker Compose*. However, I would like to avoid using containerization and instead run the simulation natively on my host OS. I understand that older versions of the Slurm source code included a native sim directory that allowed for simulations without external dependencies like Docker. Given this, I have the following technical questions: - *Native Compatibility:* Is it still feasible to compile and run a Slurm simulator natively on Ubuntu 25.10? - *Version Recommendations:* Would you recommend using a specific legacy version of Slurm that still contains the original simulation files, or is there a way to port that functionality to a more recent release? - *Configuration:* Are there specific build flags or configuration steps required to enable the simulated node environment (1,024 nodes) on a single machine without triggering the overhead of containerized networking? I would appreciate any guidance or documentation you could provide on achieving a high-node-count simulation in a "bare-metal" Linux environment. Best regards,

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GPU fallen of the bus
by Ratnasamy, Fritz 27 May '26

27 May '26

Hello, We are noticing that some of the gpus on a specific node have "fallen of the bus". We would like to remove this specific gpu from the slurm scheduler. For example, let's say GPU0 has fallen off the bus, we would need the rest of the GPU1-8 to be available and make GPU0 not able to be allocated. How can we achieve that? I have read about blacklist on the slurm forum but it seems there is no satisfying solution. Best, *Fritz Ratnasamy*Data Scientist Information Technology

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Slurm version 26.05 is now available
by Marshall Garey 26 May '26

26 May '26

We are pleased to announce the availability of Slurm 26.05. The release notes summarizing the new features, and including links to the corresponding documentation, can be found at: https://slurm.schedmd.com/release_notes.html A more extensive list of changes are available in the CHANGELOG: https://github.com/SchedMD/slurm/blob/slurm-26.05/CHANGELOG/slurm-26.05.md The Slurm documentation has also been updated to the 26.05 release: https://slurm.schedmd.com Slurm can be downloaded from: https://github.com/SchedMD/slurm/releases -- Marshall Garey Release Management, Support, and Development SchedMD LLC - Commercial Slurm Development and Support

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Core Specialization Feature
by Dan Healy 21 May '26

21 May '26

I'm curious how to report to our users that the number of available CPU cores on a given node are *(CoresPerSocket * SocketsPerBoard * ThreadsPerCore) - CpuSpecCount*. In a basic example, if the node has 32 cores and CpuSpecCount=1, then there's actually 31 cores available. If a user runs `srun -n32 -N1 bash` he/she will be denied for resources. Then, If a user runs `sinfo -O cpus,nodes` shows there's 32 cores available and the user is confused. How can the user clearly identify that in the above case, the exact number of available CPU cores available are 31 and *not* 32? -- Thanks, Daniel Healy

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cgroup error in SLURM version 25.11.2
by bradford.kerr＠srs.gov 19 May '26

19 May '26

I'm trying to install and run SLURM on a stand-alone (no network access) cluster of four PCs running Red Hat Linux 9. On the first compute node of the cluster, I can not get past the error message "cannot create cgroup context for cgroup/v2". It appears that file cgroup_v2.so does not exist. How do I get past this error?

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