knaller/Containerfile_guest at main · benben/knaller · GitHub

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FROM docker.io/library/ubuntu:26.04

RUN apt-get update && \
    DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
        openssh-server \
        systemd \
        systemd-sysv \
    && rm -rf /var/lib/apt/lists/*

# Root password for SSH access.
RUN echo 'root:root' | chpasswd

# Allow root login via SSH.
RUN sed -i 's/^#*PermitRootLogin.*/PermitRootLogin yes/' /etc/ssh/sshd_config

# DNS via kernel boot args: the kernel writes nameservers from the ip= boot
# parameter to /proc/net/pnp, so we symlink resolv.conf there.
# We can't rm /etc/resolv.conf during build (Podman bind-mounts it), so we
# use a systemd-tmpfiles rule to create the symlink on first boot.
RUN echo 'L+ /etc/resolv.conf - - - - /proc/net/pnp' > /etc/tmpfiles.d/resolv.conf

# Ensure sshd host keys are generated on first boot.
RUN systemctl enable ssh