Linux Process Debugging

A process is consuming 100% CPU on a Linux server. Walk me through how you would identify and troubleshoot this issue.

Linuxadvanced

// interview question

A process is consuming 100% CPU on a Linux server. Walk me through how you would identify and troubleshoot this issue.

Sample answer

Start with top or htop to identify the process. Use ps aux to get details. Check strace to see system calls, lsof for open files, and /proc/<pid>/ for process info. For Java/Python, get thread dumps. Check logs, and consider perf or flamegraphs for deep analysis. May indicate infinite loops, memory leaks, or resource contention.

Why this matters

Systematic troubleshooting is essential for production issues. Starting with broad tools (top) and narrowing down (strace, perf) helps identify root causes efficiently. Understanding Linux process management and debugging tools is a core DevOps skill.

Code examples

Identify high CPU process

bash

# Find top CPU consumers
top -bn1 | head -20

# Sort by CPU usage
ps aux --sort=-%cpu | head -10

# Get process details
ps -p <PID> -o pid,ppid,cmd,%cpu,%mem,etime

# Check process tree
pstree -p <PID>

Deep process analysis

bash

# Trace system calls
strace -p <PID> -c  # Summary
strace -p <PID> -f  # Follow forks

# Check open files and connections
lsof -p <PID>

# View process memory map
cat /proc/<PID>/maps

# CPU profiling with perf
perf record -p <PID> -g -- sleep 30
perf report

Common mistakes to avoid

Immediately killing the process without investigating the root cause
Not checking if the high CPU is expected (batch job, build process)
Forgetting to check system logs before diving into process-level debugging

Likely follow-ups

How would you generate a thread dump for a Java application?
What is the difference between CPU user time and system time?
How do you identify if the issue is I/O bound vs CPU bound?

Answer out loud first, then check yourself against the model answer.

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