What is docker ps -a in Docker?
docker ps -a (or docker ps --all) lists ALL containers on the system — both running and stopped. Without the -a flag, docker ps only shows currently running containers. It is one of the most frequently used Docker commands for inspecting container state, finding container IDs, and debugging.
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Up X hours/minutes — container is currently running
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Exited (0) — container stopped successfully (exit code 0 = success)
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Exited (1) — container stopped with error (non-zero = failure)
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Exited (137) — container was killed (SIGKILL — often OOM or docker kill)
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Created — container created but never started
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Paused — container is paused (docker pause was called)
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Restarting — container is in restart loop
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Removing — container is being removed
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Dead — container is in a broken state, needs force removal
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docker ps — shows ONLY running containers (STATUS: Up)
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docker ps -a — shows ALL containers regardless of state
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docker ps -q — shows only IDs of running containers
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docker ps -aq — shows only IDs of ALL containers
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docker ps -l — shows the most recently created container
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docker ps -n 5 — shows last 5 created containers
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docker ps -as — shows running containers with disk size info
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docker ps shows only running containers — always use -a to see everything
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The STATUS column is the most important — it tells you exactly why a container stopped
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Exit code 0 = clean stop, non-zero = error — use docker logs to investigate
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Use -q flag to get just IDs — essential for scripting bulk operations
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Use --filter to narrow down containers by status, name, image, or label
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Use --format for clean readable output or JSON for programmatic processing
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docker ps -aq is the foundation of most container cleanup scripts
Scenario Questions
0-2 years experience
- 1You need to verify whether a container that previously crashed is still present on the host. Which Docker command would you run, and what output would you look for?
- 2A teammate asks you to list all containers, including those that have stopped, so they can clean up old images. How would you do that?
- 3If you run `docker ps` and don't see a container you expect, what would you try next?
2-5 years experience
- 1During a CI pipeline, a test fails because a container that should be running is not listed by `docker ps`. How would you investigate using `docker ps -a` and what clues would you look for?
- 2You notice many exited containers accumulating on a host. Explain how you would use `docker ps -a` with filters to identify containers that exited more than 24 hours ago.
- 3A developer reports that `docker ps -a` shows a container with status 'Created' but it never started. What could cause this, and how would you debug it?
5-8 years experience
- 1Our monitoring system needs to periodically report the number of stopped containers across a fleet of hosts. Discuss the performance implications of using `docker ps -a` at scale and alternative approaches.
- 2Design a cleanup automation that safely removes exited containers without affecting running ones. How would you leverage `docker ps -a` output and what edge cases must you handle?
- 3Explain how you would integrate `docker ps -a` information into a centralized logging pipeline, considering high container churn and API rate limits.
8+ years experience
- 1We are moving from Docker CLI usage to a service‑oriented architecture with Kubernetes. How would you phase out reliance on `docker ps -a` in operational processes, and what replacement patterns would you propose?
- 2Across multiple teams, there is inconsistency in how container lifecycle is audited. Propose an organization‑wide policy that replaces ad‑hoc `docker ps -a` checks with a standardized observability solution.
- 3When designing a platform that supports both legacy Docker hosts and modern orchestrators, how do you ensure consistent visibility into container states without depending on `docker ps -a`?
Follow-up Questions
- Which flag would you add to `docker ps` to see only running containers?
- How can you pipe `docker ps -a` output to remove all exited containers in one command?
- What does the STATUS column tell you about a container's lifecycle?