Create random character devices so systemd does not crash

Systemd, depending on the version and the configuration,
can attempt to open urandom when a ramdisk boots, before
the udevd is launched to handle the devices. In particular
in FIPS mode, this can result in the ramdisk crashing.

In order to handle this, we pre-create the chracter device
files which can be statically used in the early start sequence
to allow the agent to boot and deploy.

Change-Id: I587e66a0d6b652c4aeca6fc211602d999d4641e8

dib/ironic-ramdisk-base/cleanup.d/99-ramdisk-create

@@ -24,6 +24,20 @@ echo "#disabled" > ./tmp/fstab.new
 sudo mv ./tmp/fstab.new ./etc/fstab
 sudo ln -s ./sbin/init ./
 
+# NOTE(TheJulia): Make a random and urandom entry to handle
+# long standing systemd bug cases where it may, depending on
+# underlying OS config/version, try to open the random number
+# generator before initializing.
+# This class of issue has appeared frquently with systemd,
+# https://github.com/systemd/systemd/issues/4167 is a commonly
+# referenced example of this behavior.
+if ! [ -a ./dev/random ]; then
+    sudo mknod ./dev/random c 1 8
+fi
+if ! [ -a ./dev/urandom ]; then
+    sudo mknod ./dev/urandom c 1 9
+fi
+
 # Note(JayF): to anyone trying to make this more configurable in the future,
 # there are significant hurdles around shell quoting if you try to put these
 # find commands into variables for making them more configurable.

releasenotes/notes/create-ramdisk-random-devices-263f78a2ef40dbe2.yaml

@@ -0,0 +1,9 @@
+---
+fixes:
+  - |
+    Fixes issues with ramdisks potentially crashing when starting due to
+    systemd attempting to access a random number generator before udevd has
+    been launched. Depending on the mode of operation and underlying
+    and configuration, i.e. in FIPS mode, the system could have crashed as
+    a result. We will now always create the character devices devices, which
+    can be used early in the boot sequence.