Is cgroup expected to work in Core? Issues found while trying rkt.

[qopit]

While experimenting with rkt [1] I'm having some issues with cgroup.  Is cgroup expected to work under Core?

I *am* currently on coreepure64 6.0 (kernel 3.16.6-tinycore64), which could obviously be relevant.

The errors that rkt is pumping out related to cgroup are:

Code: [Select]

Failed to create root cgroup hierarchy: Read-only file system
Failed to allocate manager object: Read-only file system

I'm not very familiar with cgroup, but the flat hierarchy (all zeros) here seems odd:

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$ cat /proc/cgroups
#subsys_name    hierarchy       num_cgroups     enabled
cpuset  0       1       1
cpu     0       1       1
cpuacct 0       1       1
devices 0       1       1
freezer 0       1       1
net_cls 0       1       1
blkio   0       1       1
perf_event      0       1       1
net_prio        0       1       1

and the rkt folks were surprised that nothing cgroup related showed up in /proc/1/mountinfo ...

so /proc/cgroups is saying the subsystems are enabled but you don't have them mounted, this is weird and I'm not familiar with tinycore

Does anyone have any ideas on what is up here, or any leads on where I might dig next?  Also filing a rkt issue.

[1] https://github.com/coreos/rkt

[curaga]

Why would init mount cgroups? Unless it was systemd, of course...

Does rkt require systemd? Cgroups themselves should work, as far as the kernel config options are enabled, but I haven't tested them.

[qopit]

rkt is not supposed to require systemd, but it is interesting that you asked that, as I had to check that earlier due to a warning (that looked like an error) when looking for non-existent libsystemd.

CoreOS (the origin of rkt) definitely uses systemd, and the person who expressed the surprise at cgroup not being mounted was (I think) a coreos person, so they might be used to that approach.

No clue why such a thing would end up as mounted, but systemd is totally foreign to me!

I think my takeaway here is that there is no reason for cgroup to not work properly.  I thought the "read-only file system" part of "Failed to create root cgroup hierarchy: Read-only file system" might be related to a tinycore thing somehow, but perhaps not.  I'll chase it on the rkt side.

Thanks!