This is causing LXD VMs (Focal, possibly others) to boot in "degraded"
state, see [1]. The underlying cause is:
root@paride-f-delme:~# systemctl status systemd-sysctl.service
● systemd-sysctl.service - Apply Kernel Variables
Loaded: loaded (/lib/systemd/system/systemd-sysctl.service; static; vendor
preset: enabled)
Active: failed (Result: exit-code) since Fri 2020-11-06 16:43:35 UTC;
14min ago
Docs: man:systemd-sysctl.service(8)
man:sysctl.d(5)
Main PID: 301 (code=exited, status=1/FAILURE)
root@paride-f-delme:~# /lib/systemd/systemd-sysctl
Couldn't write '176' to 'kernel/sysrq', ignoring: No such file or directory
Not setting net/ipv4/conf/all/promote_secondaries (explicit setting exists).
Not setting net/ipv4/conf/default/promote_secondaries (explicit setting exists).
Couldn't write 'fq_codel' to 'net/core/default_qdisc', ignoring: No such file
or directory
Couldn't write '4194304' to 'kernel/pid_max': Invalid argument
[1] https://paste.ubuntu.com/p/TQhpFWYzK7/
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https://bugs.launchpad.net/bugs/1866149
Title:
CONFIG_BASE_SMALL=1 restricts pid space, which conflicts with systemd
default sysctl
Status in linux-kvm package in Ubuntu:
Confirmed
Bug description:
I'm not completely sure which package to log this against.
I'm running the kvm focal minimal cloud image from 20200302. I noticed
on boot that there was an error complaining that systemd-systemctl
couldn't update pid_max to the value it wanted:
systemd-sysctl[117]: Couldn't write '4194304' to 'kernel/pid_max':
Invalid argument
Digging into it a bit more, this comes from /usr/lib/sysctl.d/50-pid-max.conf:
# Bump the numeric PID range to its maximum of 2^22 (from the in-kernel
default
# of 2^16), to make PID collisions less likely.
kernel.pid_max = 4194304
However, the linux-image-kvm kernel is compiled with
CONFIG_BASE_SMALL=1
and this triggers the following code in include/linux/threads.h
#define PID_MAX_LIMIT (CONFIG_BASE_SMALL ? PAGE_SIZE * 8 : \
(sizeof(long) > 4 ? 4 * 1024 * 1024 : PID_MAX_DEFAULT))
which means that if CONFIG_BASE_SMALL is set we get a maximum limit of
PAGE_SIZE * 8, which on x86 would be 32768.
As a workaround I can override it with a file in /etc/sysctl.d/ but
this shouldn't be needed.
I really don't know if CONFIG_BASE_SMALL makes any sense on x86 cloud
images, they really aren't small machines in the scheme of things!
Cheers
David
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