There are times when you want to go inside a Docker container and use a shell. Normally, you would use the following command to enter the container, but on the Alpine base, you would use ash instead of bash to enter the container.

$ docker run --rm -t -i centos:centos7 /bin/bash

s

$ docker run --rm -t -i alpine:latest /bin/ash

参考
Dockerコンテナのシェルの中に入る dockerでalpine linux ベースのcontainerに入って、shellを使いたいとき。