CRI-O conmon Error — Quick Fix

In this tutorial, you'll learn about CRI. We cover key concepts, practical examples, and best practices.

The Problem

CRI-O conmon (container monitor) fails or crashes when starting containers. The conmon process OOM-kills, fails to find the container runtime (runc/crun), or cannot attach to the container's stdio. Pods may remain stuck in ContainerCreating.

Error example:

Error: conmon: command not found
Error: conmon: failed to set up container stdio: no such file or directory
Container runtime error: conmon killed by signal 9 (OOM)

The Fix

Step 1: Verify conmon installation

WRONG — running the container runtime directly:

# Bypassing conmon means losing container process tracking

RIGHT — check conmon is installed and in PATH:

which conmon

Output:

/usr/bin/conmon

If not found, install it:

# Debian/Ubuntu
apt install conmon

# RHEL/CentOS
dnf install conmon

Step 2: Check conmon version compatibility

WRONG — mixing conmon versions from different sources:

# conmon must match the CRI-O version

RIGHT — verify the version:

conmon --version

# Compare with CRI-O version
crio --version

If they are from different major versions, upgrade conmon:

# Install the matching version
dnf update conmon
systemctl restart crio

Use DodaTech's Runtime Compatibility Checker to validate conmon, CRI-O, and runc/crun version alignment across all nodes.

Prevention Tips

• Install conmon from the same repository as CRI-O to ensure version compatibility
• Monitor conmon OOM kills with systemd journal
• Set proper memory limits for conmon in the systemd service
• Use crun instead of runc for better conmon performance
• Use DodaTech's Pod Startup Analyzer to detect conmon-related delays

Common Mistakes with o conmon error

1. Placing the wildcard pattern first in case expressions, making all subsequent patterns unreachable
2. Using head and tail instead of pattern matching, causing runtime errors on empty lists
3. Forgetting that lazy evaluation defers computation until the value is forced, causing space leaks with unevaluated thunks

These mistakes appear frequently in real-world CRI code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ

Related: DodaTech's Container Runtime Optimizer provides recommendations for conmon configuration, runtime selection, and resource allocation for optimal container startup performance.