The 'Why Won't It Start?' Checklist

~14 min · debug

Level 0Container Curious

0 XP0/36 lessons0/10 achievements

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The seven steps in order

docker ps -a | grep myapp — does the container exist? What's its status?
docker logs --tail 100 myapp — what did it say before dying?
docker inspect myapp --format '{{.State.ExitCode}}' — what was the exit code?
docker run -it --rm <image> sh — can you even start a shell from this image?
docker exec -it myapp sh — if it's running but broken, get inside.
docker port myapp — are ports actually mapped?
docker network inspect <net> — is it on the right network with the right peers?

Code

Walk the checklist·bash

# 1
docker ps -a --format 'table {{.Names}}\t{{.Status}}\t{{.Image}}'

# 2
docker logs --tail 100 myapp

# 3
docker inspect myapp --format 'state={{.State.Status}} exit={{.State.ExitCode}}'

# 4 — sanity check the image itself
docker run -it --rm myapp:1.0 sh

# 5 — get inside a running but broken container
docker exec -it myapp sh

# 6
docker port myapp

# 7
docker network inspect bridge

External links

Docker — Troubleshooting

Exercise

Intentionally break a container three different ways: (a) wrong CMD path, (b) port already in use, (c) missing env var the app reads at startup. For each, walk the 7-step checklist and identify which step revealed the cause.

Progress

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