Dockerfile

FROM centos:7

ENV container=docker

# The package `systemd-sysv` and `initscripts`
# are installed for providing backwards compatibility
# with some services and they are also needed for functioning
# of the `sshd-keygen` service.
RUN yum -y install dnf \
    && dnf -y upgrade \
    && dnf -y install \
        systemd \
        systemd-sysv \
        initscripts \
        pam \
        epel-release \
        openssh-server \
        curl \
        wget \
        iproute \
        mc \
        nano \
        which \
        man \
        man-pages \
        cronie \
    && dnf clean all \
    && yum clean all

# Modified version of: https://hub.docker.com/r/centos/systemd/dockerfile
RUN rm -f \
        /lib/systemd/system/sockets.target.wants/*udev* \
        /lib/systemd/system/sockets.target.wants/*initctl* \
        /etc/systemd/system/*.wants/* \
    && cp -r /lib/systemd/system/sockets.target.wants/ /etc/systemd/system/ \
    && systemctl disable systemd-vconsole-setup.service \
    && systemctl disable systemd-udevd.service \
    && mkdir -p /etc/systemd/system/sys-fs-fuse-connections.mount.d/ \
    && echo -e '[Unit]\nConditionPathExists=/sys/fs/fuse/connections\nConditionCapability=CAP_SYS_ADMIN\nConditionVirtualization=!private-users\n' > /etc/systemd/system/sys-fs-fuse-connections.mount.d/docker-virt.conf \
    && mkdir -p /etc/systemd/system/console-getty.service.d/ \
    && echo -e '[Service]\nExecStart=\nExecStart=-/sbin/agetty --autologin root --noclear --keep-baud console 115200,38400,9600 $TERM\n' > /etc/systemd/system/console-getty.service.d/docker-virt.conf


# The service `docker-ipv6-hosts-cleanup` removes IPv6 entries from `/etc/hosts`
# so daemons (e.g. postfix) do not expect these interfaces to be available.
# IPv6 loopback is not supported at all with Docker for Mac (and probably Docker Desktop at all).
RUN rm -f /etc/init.d/net* /run/nologin /var/run/nologin \
    && echo -e "[Unit]\nDescription=Remove IPv6 hosts entries\nBefore=network.target\n\n[Service]\nType=oneshot\nRemainAfterExit=true\nStandardOutput=journal\nExecStart=/usr/bin/sed -r -i -c '/^[:0-9a-f]+\\\\\s+/d' /etc/hosts\n\n[Install]\nWantedBy=multi-user.target" > /etc/systemd/system/docker-ipv6-hosts-cleanup.service \
    && systemctl enable docker-ipv6-hosts-cleanup.service \
    && sed -ri '0,/^#?\s*(PermitRootLogin)\s+.*$/s//\1 yes/' /etc/ssh/sshd_config \
    && sed -ri '0,/^#?\s*(PubkeyAuthentication)\s+.*$/s//\1 yes/' /etc/ssh/sshd_config \
    && sed -ri '0,/^#?\s*(AllowAgentForwarding)\s+.*$/s//\1 yes/' /etc/ssh/sshd_config \
    && sed -ri '0,/^#?\s*(PermitTTY)\s+.*$/s//\1 yes/' /etc/ssh/sshd_config \
    && sed -ri '0,/^#?\s*(AllowTcpForwarding)\s+.*$/s//\1 yes/' /etc/ssh/sshd_config \
    && sed -ri '0,/^#?\s*(MaxAuthTries)\s+.*$/s//\1 10/' /etc/ssh/sshd_config \
    && sed -ri '0,/^#?\s*(ListenAddress)\s+.*$/s//\1 0.0.0.0/' /etc/ssh/sshd_config \
    && systemctl enable sshd.service \
    && sed -ri '0,/^#?\s*(Compress)\s*=\s*.*$/s//\1=no/' /etc/systemd/journald.conf \
    && sed -ri '0,/^#?\s*(SystemMaxUse)\s*=\s*.*$/s//\1=50M/' /etc/systemd/journald.conf \
    && sed -ri '0,/^#?\s*(RuntimeMaxUse)\s*=\s*.*$/s//\1=5%/' /etc/systemd/journald.conf \
    && sed -ri '0,/^#?\s*(SyncIntervalSec)\s*=\s*.*$/s//\1=15m/' /etc/systemd/journald.conf \
    && sed -ri '0,/^#?\s*(RateLimitInterval)\s*=\s*.*$/s//\1=10s/' /etc/systemd/journald.conf \
    && sed -ri '0,/^#?\s*(RateLimitBurst)\s*=\s*.*$/s//\1=100/' /etc/systemd/journald.conf \
    && sed -ri '0,/^#?\s*(MaxRetentionSec)\s*=\s*.*$/s//\1=1day/' /etc/systemd/journald.conf \
    && sed -ri '0,/^#?\s*(ForwardToConsole)\s*=\s*.*$/s//\1=no/' /etc/systemd/journald.conf \
    && sed -ri '0,/^#?\s*(MaxLevelConsole)\s*=\s*.*$/s//\1=err/' /etc/systemd/journald.conf \
    && echo 'centos' | passwd --stdin root \
    && echo -e "*** Welcome to interactive tty of full CentOS operating system running on docker! ***\n\nLogin: root\nPass: centos\n" > /etc/issue \
    && echo -e "\nHint: You can terminate the container by shutting the system down - run the 'halt' command\n" > /etc/motd

HEALTHCHECK --interval=3s --timeout=2m --start-period=4s --retries=15 CMD ["/usr/bin/systemctl", "is-system-running", "--quiet"]

# This is the proper shutdown signal used by systemd init process
# Vide: https://www.freedesktop.org/software/systemd/man/systemd.html#Signals
STOPSIGNAL SIGRTMIN+4

VOLUME ["/sys/fs/cgroup", "/tmp"]

EXPOSE 22
USER root

CMD ["/sbin/init"]