Public bug reported:
The kernel.pid_max sysctl defaults to 32768. This is a very historic
limit to provide compatibility with ancient binaries.
Moving on to the year 2020 multicore CPU:s for desktops, laptops and
servers is the standard, and together with PID randomization wraparound
happens rather quickly on many-core machines with lots of activity.
Wraparounds in itself is not a big issue, but there are corner cases
like scripts that checks if a PID is alive etc that run into trouble if
another process has started using the PID it expects, scripts
(erroneously) using PIDs for work/temporary files, etc.
To avoid problems within the lifetime of Ubuntu Focal, it's time to
increase kernel.pid_max by default in the distribution by including
tuning in a file in /etc/sysctl.d/
Our suggestion is to ship the following tuning by default:
# Make PID-rollover not happen as often.
# Default is 32768
kernel.pid_max = 999999
with the following motivation:
1) It achieves a 30-fold increase in the available number-space,
reducing the likelihood of PID wraparound/collisions.
2) It only adds one digit to the PID, so it's still possible to remember
a PID
3) Output in top, ps, etc is still nicely readable
3) We have used it for years on Ubuntu 14.04 and onwards, on 1000+
machines and with a wide array of commercial and scientific software
without any issues.
4) One could argue that it is a preventive security measure, there are a
lot of weirdly written scripts and software out there that behaves badly
upon PID reuse/collissions.
** Affects: procps (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1867949
Title:
It's time to increase the default pid_max from 32768 to avoid PID
wraparounds/collossions
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