====== Docker Troubleshooting ======

===== About Namespaces =====

[[https://www.redhat.com/sysadmin/container-namespaces-nsenter]]

===== Network =====

==== Enter Namespace ====

<code bash>
container_id="mycontainerid"
container_pid="$(docker inspect --format "{{ .State.Pid }}" "${container_id}")"
nsenter -n -t "${container_pid}"
exit
</code>

After executing nsenter all commands that support namespaces see the network interfaces like they are in the container. Example commands: ip, tcpdump. With exit the namespace can be left to see the network interfaces from the host system again.

==== tcpdump in Container ====

tcpdump has to be installed on the host system and not in the container.

<code bash>
container_id="mycontainerid"
container_pid="$(docker inspect --format "{{ .State.Pid }}" "${container_id}")"
nsenter -n -t "${container_pid}" tcpdump -nn -i eth0
</code>