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** Changed in: linux (Ubuntu)
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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 package in Ubuntu:
Incomplete
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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