Processes of nixbld user “terminated abnormally without generating a coredump”, with no build going on

Since January 4, from time to time I get errors like the following:

Apr 02 07:27:10 server systemd[1]: Created slice Slice /system/systemd-coredump.
Apr 02 07:27:10 server systemd[1]: Started Process Core Dump (PID 176241/UID 0).
Apr 02 07:27:10 server systemd[1]: Started Process Core Dump (PID 176246/UID 0).
Apr 02 07:27:10 server systemd[1]: Started Process Core Dump (PID 176247/UID 0).
Apr 02 07:27:10 server systemd[1]: Started Process Core Dump (PID 176248/UID 0).
Apr 02 07:27:10 server systemd[1]: Started Process Core Dump (PID 176256/UID 0).
Apr 02 07:27:10 server systemd-coredump[176250]: Resource limits disable core dumping for process 176230 (opt).
Apr 02 07:27:10 server systemd-coredump[176250]: Process 176230 (opt) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:27:10 server systemd-coredump[176253]: Process 176238 (opt) of user 30013 terminated abnormally without generating a coredump.
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[on the order of 100 similar lines]
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Apr 02 07:27:32 server systemd-coredump[178304]: Process 178293 (llc) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:27:35 server systemd-coredump[179029]: Process 179007 (llc) of user 30013 terminated abnormally without generating a coredump.
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[on the order of 100 similar lines]
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Apr 02 07:41:23 server systemd-coredump[294121]: Process 294096 (llvm-lto) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:42:43 server systemd-coredump[316281]: Process 316250 (llvm-mc) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:42:43 server systemd-coredump[316290]: Process 316262 (llvm-mc) of user 30013 terminated abnormally without generating a coredump.
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[on the order of 100 similar lines]
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Apr 02 07:44:05 server systemd-coredump[339045]: Process 339022 (llvm-readobj) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:44:08 server systemd-coredump[339887]: Process 339854 (llvm-objdump) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:44:08 server systemd-coredump[339924]: Process 339900 (llvm-objdump) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:44:10 server systemd-coredump[340655]: Process 340631 (opt) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:44:10 server systemd-coredump[340818]: Process 340781 (opt) of user 30013 terminated abnormally without generating a coredump.
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Apr 02 07:44:48 server systemd-coredump[349030]: Process 349008 (llvm-lto2) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:46:20 server systemd-coredump[372923]: Process 372783 (opt) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:47:01 server systemd-coredump[383459]: Process 383435 (llvm-lto2) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:47:01 server systemd-coredump[383553]: Process 383520 (llvm-lto2) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:47:46 server systemd-coredump[396384]: Process 396362 (llvm-readobj) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:47:46 server systemd-coredump[396489]: Process 396465 (llvm-readobj) of user 30013 terminated abnormally without generating a coredump.
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Apr 02 07:48:37 server systemd-coredump[412845]: Process 412841 (IRTests) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:48:39 server systemd-coredump[413001]: Process 412987 (SupportTests) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:48:41 server systemd-coredump[413303]: Process 413290 (opt) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:48:50 server systemd-coredump[414856]: Process 414831 (opt) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:48:50 server systemd-coredump[414858]: Process 414830 (opt) of user 30013 terminated abnormally without generating a coredump.
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Apr 02 07:48:51 server systemd-coredump[415035]: Process 414988 (opt) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:48:51 server systemd-coredump[415034]: Process 415010 (opt) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:49:07 server systemd-coredump[417209]: Process 417204 (IslTests) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:49:07 server systemd-coredump[417230]: Process 417222 (IslTests) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:49:08 server systemd-coredump[417241]: Process 417234 (IslTests) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:49:08 server systemd-coredump[417266]: Process 417256 (IslTests) of user 30013 terminated abnormally without generating a coredump.
Apr 02 07:49:08 server systemd-coredump[417280]: Process 417273 (IslTests) of user 30013 terminated abnormally without generating a coredump.

Relevant information:

  • This seems to happen a few days after switching to a new NixOS configuration.
  • I do not remember when I switched to nixos-23.11 (from nixos-23.05) but it might have been shortly before when (Jan 4) I first started getting these error messages.
  • As far as I can tell, no nix build or other nix activity is going on when these errors occur.
% grep 30013 /etc/passwd
nixbld13:x:30013:30000:Nix build user 13:/var/empty:/run/current-system/sw/bin/nologin

Any ideas what the problem could be?