How to Debug CrashLoopBackOff in Kubernetes

A systematic approach to diagnosing and fixing CrashLoopBackOff errors in Kubernetes pods.

Marcus LeeFebruary 18, 20262 min read

CrashLoopBackOff is one of the most common Kubernetes errors, and one of the most poorly explained by kubectl get pods alone. Here's how to actually diagnose it.

Step 1: Confirm what's happening

bash

kubectl get pods

NAME                READY   STATUS             RESTARTS   AGE
api-7d9f8c9d-x2n4q   0/1     CrashLoopBackOff   6          4m

The status means: the container starts, exits (crashes or completes), and Kubernetes keeps restarting it with an increasing backoff delay.

Step 2: Read the logs from the crashed container

bash

kubectl logs api-7d9f8c9d-x2n4q --previous

The --previous flag is essential — it shows logs from the last terminated container, not the current (likely empty) restart attempt.

Step 3: Check the exit code and reason

bash

kubectl describe pod api-7d9f8c9d-x2n4q

Look at the Last State section:

Last State:     Terminated
  Reason:       Error
  Exit Code:    1

Common exit codes:

Exit Code	Meaning
0	Container exited cleanly (often a misconfigured entrypoint for a long-running service)
1	Application error — check logs
137	OOMKilled — the container exceeded its memory limit
143	SIGTERM — often a graceful shutdown that took too long

Step 4: Match the exit code to a fix

OOMKilled (137): Raise the memory limit or fix a memory leak.

yaml

resources:
  limits:
    memory: "512Mi"
  requests:
    memory: "256Mi"

Application error (1): Usually a missing environment variable, bad config, or failed dependency connection — the logs from Step 2 will show the stack trace.

Readiness/liveness probe failing: If the app takes longer to boot than the probe allows, increase initialDelaySeconds.

yaml

livenessProbe:
  httpGet:
    path: /healthz
    port: 8080
  initialDelaySeconds: 30
  periodSeconds: 10

Step 5: Verify the fix

bash

kubectl rollout restart deployment api
kubectl get pods -w

Watch for RESTARTS to stop increasing and STATUS to settle on Running.

Quick reference checklist

kubectl logs <pod> --previous
kubectl describe pod <pod> and check the exit code
Match exit code to cause (OOM, app error, probe timeout)
Apply the fix and roll out again

#kubernetes #devops #cloud

Marcus Lee

Cloud & DevOps Engineer

Marcus covers Kubernetes, cloud infrastructure, and CI/CD. He's spent a decade running production systems at scale.

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