sysctl: let's by default increase the numeric PID range from 2^16 to 2^22

This should PID collisions a tiny bit less likely, and thus improve
security and robustness.

2^22 isn't particularly a lot either, but it's the current kernel
limitation.

Bumping this limit was suggested by Linus himself:

https://lwn.net/ml/linux-kernel/CAHk-=wiZ40LVjnXSi9iHLE_-ZBsWFGCgdmNiYZUXn1-V5YBg2g@mail.gmail.com/

Let's experiment with this in systemd upstream first. Downstreams and
users can after all still comment this easily.

Besides compat concern the most often heard issue with such high PIDs is
usability, since they are potentially hard to type. I am not entirely sure though
whether 4194304 (as largest new PID) is that much worse to type or to
copy than 65563.

This should also simplify management of per system tasks limits as by
this move the sysctl /proc/sys/kernel/threads-max becomes the primary
knob to control how many processes to have in parallel.

Resolves: #1744214

diff --git a/sysctl.d/50-pid-max.conf b/sysctl.d/50-pid-max.conf
new file mode 100644 (file)
index 0000000..3a8393d
--- /dev/null
+++ b/sysctl.d/50-pid-max.conf
@@ -0,0 +1,17 @@
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU Lesser General Public License as published by
+#  the Free Software Foundation; either version 2.1 of the License, or
+#  (at your option) any later version.
+
+# See sysctl.d(5) and core(5) for documentation.
+
+# To override settings in this file, create a local file in /etc
+# (e.g. /etc/sysctl.d/90-override.conf), and put any assignments
+# there.
+
+# 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
+

diff --git a/sysctl.d/meson.build b/sysctl.d/meson.build
index 64f6ce942edd6bd6f8c9f61aaeaca0744265ba44..a95957ad7d4afa73dbde471a1726f94adffd5538 100644 (file)
--- a/sysctl.d/meson.build
+++ b/sysctl.d/meson.build
@@ -2,6 +2,7 @@
 
 install_data(
         '50-default.conf',
+        '50-pid-max.conf',
         install_dir : sysctldir)
 
 in_files = []