Add Dockerfile example of container image running Systemd (securely)

Author: rodnymolina

dockerfiles/ubuntu-bionic-systemd/Dockerfile

@@ -0,0 +1,59 @@
+# Nestybox's systemd dockerfile.
+#
+# Description:
+#
+# Image's goal is to serve as a basic building-block for users looking to
+# run various background processes (daemons) in Nestybox's system containers.
+# For this purpose we are installing systemd process-manager as part of this
+# Dockerfile.
+#
+#
+# Container initialization:
+#
+# $ docker run --runtime=sysbox-runc \
+#        -it --rm --name=sys-cont nestybox/ubuntu-bionic-systemd
+#
+
+FROM ubuntu:bionic
+
+#
+# Systemd installation
+#
+RUN apt-get update &&                            \
+    apt-get install -y --no-install-recommends   \
+            systemd                              \
+            systemd-sysv                         \
+            libsystemd0                          \
+            ca-certificates                      \
+            dbus                                 \
+            iptables                             \
+            iproute2                             \
+            kmod                                 \
+            locales                              \
+            sudo                                 \
+            udev &&                              \
+                                                 \
+    # Prevents journald from reading kernel messages from /dev/kmsg
+    echo "ReadKMsg=no" >> /etc/systemd/journald.conf &&               \
+                                                                      \
+    # Housekeeping
+    apt-get clean -y &&                                               \
+    rm -rf                                                            \
+       /var/cache/debconf/*                                           \
+       /var/lib/apt/lists/*                                           \
+       /var/log/*                                                     \
+       /tmp/*                                                         \
+       /var/tmp/*                                                     \
+       /usr/share/doc/*                                               \
+       /usr/share/man/*                                               \
+       /usr/share/local/* &&                                          \
+                                                                      \
+    # Create default 'admin/admin' user
+    useradd --create-home --shell /bin/bash admin && echo "admin:admin" | chpasswd && adduser admin sudo
+
+
+# Make use of stopsignal (instead of sigterm) to stop systemd containers.
+STOPSIGNAL SIGRTMIN+3
+
+# Set systemd as entrypoint.
+ENTRYPOINT [ "/sbin/init" ]