Add warning about cgroup v1 force flag #2749
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| @@ -172,7 +172,8 @@ any other tasks on the same CPU core the judgedaemon is using: | |||
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| On modern distros (e.g. Debian bullseye and Ubuntu Jammy Jellyfish) which have | |||
| cgroup v2 enabled by default, you need to add ``systemd.unified_cgroup_hierarchy=0`` | |||
| as well. Then run ``update-grub`` and reboot. | |||
| as well. If you are running systemd v257, you also need to add `SYSTEMD_CGROUP_ENABLE_LEGACY_FORCE=1`. | |||
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They say they will drop it fully in 248, so no
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I'm currently running v256 and I can't run with cgroup v1 at all.
If I remember correctly, only v255 requires this extra command-line parameter, and in v256, support was dropped entirely, so the flag is no longer needed there.
It may also be nice to warn users about this, something like: "Support for cgroup v1 is dropped entirely in systemd v256 or higher. DOMjudge will support cgroup v2 starting from version 8.4."
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https://github.com/systemd/systemd/blob/main/NEWS seems to suggest that for 257:
* Support for cgroup v1 ('legacy' and 'hybrid' hierarchies) is now considered obsolete and systemd by default will refuse to boot under it. To forcibly reenable cgroup v1 support, SYSTEMD_CGROUP_ENABLE_LEGACY_FORCE=1 must be set on kernel command line. The complete removal of cgroup v1 is scheduled for v258.
You are saying this is wrong?
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Oh, never mind, I misremembered 🙂 Looking back at #1072 (comment), enabling cgroup v1 in v256 makes it harder to boot the host machine (i.e. they've added a 30 second timeout) 😅
On the other hand, @RagnarGrootKoerkamp couldn't boot his Arch at all anymore (#1072 (comment)). I assume he also ran v256 back then, though (because v257 is not released yet) 🤔
In any case, the kernel parameter appears to have been necessary since v256, which is confirmed by #1072 (comment). The command-line parameter is indeed not mentioned in the v255 changelog.
Systemd 257 (currently used on arch at least) stops users from booting if you don't set this flag. Although cgroup v2 support is on its way, we might want to warn current users.