Docker: any way to list open sockets inside a running docker container?

Question

I would like to execute netstat inside a running docker container to see open TCP sockets and their statuses. But, on some of my docker containers, netstat is not available. Is

Answer 1

You can use the nsenter command to run a command on your host inside the network namespace of the Docker container. Just get the PID of your Docker container:

docker inspect -f '{{.State.Pid}}' container_name_or_id

For example, on my system:

$ docker inspect -f '{{.State.Pid}}' c70b53d98466
15652

And once you have the PID, use that as the argument to the target (-t) option of nsenter. For example, to run netstat inside the container network namespace:

$ sudo nsenter -t 15652 -n netstat
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State      
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN     

Notice that this worked even though the container does not have netstat installed:

$ docker exec -it c70b53d98466 netstat
rpc error: code = 13 desc = invalid header field value "oci runtime error: exec failed: container_linux.go:247: starting container process caused \"exec: \\\"netstat\\\": executable file not found in $PATH\"\n"

(nsenter is part of the util-linux package)

Answer 2

server:docker container ls

CONTAINER ID    IMAGE              COMMAND                  CREATED          STATUS           PORTS       NAMES

80acfa804b59    admirito/gsad:10   "docker-entrypoint.s…"   18 minutes ago   Up 10 minutes    80/tcp      gvmcontainers_gsad_1

Answer 3

The two commands from @larsks answer merged into one-liner - no need to copy-paste the PID(s) (just replace container_name_or_id):

sudo nsenter -t $(docker inspect -f '{{.State.Pid}}' container_name_or_id) -n netstat