Looking Inside: logs & exec

Your Two Debugging Superpowers

docker logs shows everything the main process wrote to stdout/stderr - in containers, apps log to the console, not to files:

$ docker logs web              # everything so far
$ docker logs -f web           # follow live (like tail -f)
$ docker logs --tail 50 web    # last 50 lines

docker exec runs an extra command inside a running container:

$ docker exec web ls /usr/share/nginx/html    # one-off command
$ docker exec -it web sh                      # interactive shell

Scenario: Production serves the wrong page. Instead of redeploying, you docker exec -it web sh, look at the actual files nginx is serving, and spot the stale index.html in seconds. Then you fix the image so the next deploy is correct.

Warning: Changes made via exec live in the container's writable layer - they vanish when the container is removed and they're not in the image. exec is for diagnosis and emergency hotfixes, never for permanent configuration.

Housekeeping:

$ docker stop web     # graceful (SIGTERM, then SIGKILL after 10s)
$ docker rm web       # remove a stopped container
$ docker rm -f web    # stop + remove in one step