I need to set the default CPU affinity for all the daemons managed by systemd, except a specific service.

Setting service's CPU affinity at /etc/systemd/system/myname.service.d/scheduler.conf works just fine, so I guessed I could set my service affinity to, say, cores 2-11, and let the rest of the system to live with cores 0-1.

It seems I can't.

I tried /etc/systemd/system.conf.d/default.conf and even changed /etc/systemd/system.conf.

All the daemons (except my one) still start with all the CPUs allowed.

It seems too much hassle to setup an override /etc/systemd/system/*.service.d configuration file for each other system service.

The systemd version is 215 (from Debian Jessie)

Update: I revisited /etc/systemd/system.conf and found that I misspelled the CPU cores list. I experimented a bit more and found that, although I can setup default CPU Affinity in /etc/systemd/system.conf, the setting in /etc/systemd/system.conf.d/ doesn't seem to have any effect.

I would prefer to keep this setting in /etc/systemd/system.conf.d/scheduler.conf as the whole fleet is managed by ansible. I found a couple of examples at github with the section ([Manager]) line absent, but this doesn't work for me, too. Documentation clearly mention /etc/systemd/system.conf.d. What do I miss?

  • I don't have a way to test this, but did you check CPUAffinity parameter in /etc/systemd/system.conf, that should configure default cpuaffinity for init process and thus all other daemons
    – VenkatC
    Commented Nov 17, 2015 at 14:17
  • Well, I tried it first by misspeeled the CPU list. This does solve the issue indeed but it's a bit inconvenient as all the servers are managed by ansible and placing configuration file into system.conf.d is much better that changing system default file Commented Nov 17, 2015 at 14:47

1 Answer 1


Ok, apparently the v215 from Jessie doesn't support /etc/systemd/system.conf.d at all (see src/core/main.c:parse_config_file).


The case is closed, though.

  • Thanks for figuring this out. FWIW, this was introduced in v228 Commented Jul 15, 2020 at 19:34

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