attempt to work around container runner limitations

custom/testing/entrypoint.py

@@ -1,4 +1,4 @@
-#! env python3
+#!/usr/bin/python3
 """
 Systemd entrypoint hack.
 

custom/testing/systemd-ubuntu-22.04.Dockerfile

@@ -1,5 +1,8 @@
 FROM ubuntu:22.04
 
+COPY 01_nodoc /etc/dpkg/dpkg.cfg.d/01_nodoc
+COPY entrypoint.py entrypoint.py
+
 # init and systemd are the only real requirements for systemd.
 #
 # tar wget x-utils can be used to fetch and extract a salt onedir.
@@ -8,18 +11,23 @@ FROM ubuntu:22.04
 # states.
 #
 # tree is used by workflows for debugging
+#
+# coreutils provides tail
 RUN apt update -y \
   && echo 'tzdata tzdata/Areas select America' | debconf-set-selections \
   && echo 'tzdata tzdata/Zones/America select Phoenix' | debconf-set-selections \
   && DEBIAN_FRONTEND="noninteractive" apt install -y \
-  tree tar wget xz-utils apt-utils systemd python3 python3-pip python3-venv git
+  coreutils tree tar wget xz-utils apt-utils systemd python3 python3-pip python3-venv git \
+  && chmod +x entrypoint.py \
+  && mv /usr/bin/tail /usr/bin/tail.real
 
-COPY 01_nodoc /etc/dpkg/dpkg.cfg.d/01_nodoc
-COPY entrypoint.py entrypoint.py
 # Set the root password, this was done before single user mode worked.
 # RUN echo "root\nroot" | passwd -q root
 # RUN echo "systemd.debug_shell=tty1" >> /etc/sysctl.conf
 COPY rescue.service /etc/systemd/system/rescue.service.d/override.conf
+COPY tail /usr/bin/tail
+
+RUN chmod +x /usr/bin/tail
 
-ENTRYPOINT [ "/usr/bin/python3", "entrypoint.py" ]
+ENTRYPOINT [ "/entrypoint.py" ]
 CMD [ "/bin/bash" ]

custom/testing/tail

@@ -0,0 +1,39 @@
+#!/usr/bin/python3
+"""
+Systemd entrypoint hack.
+
+Writes /cmd.sh from the arguments passed to the script. Then execve systemd so
+systemd will be process 1. The target rescue will execute /cmd.sh using /bin/sh.
+This is needed so our ENTRYPOINT can be systemd with a target and CMD can be
+customized at runtime as expected.
+"""
+from __future__ import annotations
+
+import os
+import sys
+
+
+def run_execve(cmd, args=None):
+    if args is None:
+        args = []
+    args = [cmd] + args
+    os.environ["PYTHONPATH"] = os.pathsep.join(sys.path)
+    if os.execve in os.supports_fd:
+        with open(cmd, "rb") as fp:
+            os.execve(fp.fileno(), args, os.environ)
+    else:
+        args = [cmd] + args
+        os.execve(cmd, args, os.environ)
+
+
+pid = os.getpid()
+if pid != 0:
+    cmd = "/usr/bin/tail.real"
+    run_execve(cmd, sys.argv[1:])
+else:
+    with open("/cmd.sh", "w") as fp:
+        if sys.argv[1:]:
+            fp.write(f"tail.real", sys.argv[1:])
+        else:
+            fp.write(f"tail.real")
+    run_execve("/usr/lib/systemd/systemd", ["--systemd", "--unit=rescue.target"])