Update README.md

Author: weizhouapache

README.md

@@ -1,2 +1,73 @@
 # docker-systemd
 The docker containers with systemd support
+
+## Introduction
+
+The systemd is not supported by default in official docker images.
+
+For example, users will get the following error when start `ssh` service using systemctl in docker container
+```
+root@f3ff816528f4:/# systemctl restart ssh 
+System has not been booted with systemd as init system (PID 1). Can't operate.
+Failed to connect to bus: Host is down
+```
+
+To fix the issue, some changes are needed when build the docker images.
+- For rockylinux, almalinux and oraclelinux, refer to https://hub.docker.com/r/rockylinux/rockylinux
+- For ubuntu24 and debian12, refer to https://blog.cloudabc.eu/linux/container/2024/10/27/ubuntu-docker-container-systemd/
+
+## Build the docker images
+
+If you use a non-root user, please add `sudo` before the commands.
+```
+docker build . --file Dockerfile.ubuntu24 --tag weizhouapache/docker-systemd:latest-ubuntu24
+docker build . --file Dockerfile.debian12 --tag weizhouapache/docker-systemd:latest-debian12
+docker build . --file Dockerfile.alma9 --tag weizhouapache/docker-systemd:latest-alma9
+docker build . --file Dockerfile.oracle9 --tag weizhouapache/docker-systemd:latest-oracle9
+docker build . --file Dockerfile.rocky9 --tag weizhouapache/docker-systemd:latest-rocky9
+```
+
+You can find the docker images ready for use on:
+https://hub.docker.com/repository/docker/weizhouapache/docker-systemd/
+
+## Create docker containers
+
+Please note, the container name, hostname, network name (`net`) and ip address (`ip`) are optional.
+
+### Rocky9/Alma9/Oracle9 containers
+
+    docker run -it -d \
+        --privileged \
+        --volume=/sys/fs/cgroup:/sys/fs/cgroup:rw \
+        --cgroupns=host \
+        --name alma9 \
+        --hostname=alma9 \
+        --net=<network name> \
+        --ip=<ip address> \
+        weizhouapache/docker-systemd:latest-alma9
+
+### Ubuntu24/Debian12 containers
+
+    docker run -it -d \
+        --privileged \
+        --name ubuntu24 \
+        --hostname=ubuntu24 \
+        --net=<network name> \
+        --ip=<ip address> \
+        weizhouapache/docker-systemd:latest-ubuntu24
+
+## Access the docker containers
+
+Users can access the docker containers from the host by
+```
+docker exec -it ubuntu24 bash
+docker exec -it alma9 bash
+```
+
+The `openssh-server` package has been installed in all containers, users can enable ssh by
+```
+echo "root:password" |chpasswd
+echo "PermitRootLogin yes" >>/etc/ssh/sshd_config
+systemctl enable ssh || systemctl enable sshd
+systemctl restart ssh || systemctl restart sshd
+```