Top 50 Debugging Commands

These are the commands engineers reach for during incidents: process checks, ports, logs, services, containers, filesystems and network validation.

Debugging Reference

#	Command	Brief Description	Example
1	`ps aux \| grep java`	Find Java processes	`ps aux \| grep java`
2	`pgrep -af spring`	Find process by full command	`pgrep -af spring`
3	`lsof -i :8080`	See who is using a port	`lsof -i :8080`
4	`ss -tulnp`	List listening ports and owners	`ss -tulnp`
5	`netstat -tulnp`	Legacy port listing	`netstat -tulnp`
6	`top`	See CPU and memory hot spots live	`top`
7	`htop`	Friendlier process monitor	`htop`
8	`free -h`	Check memory usage quickly	`free -h`
9	`vmstat 1 5`	CPU, memory, IO overview	`vmstat 1 5`
10	`iostat -xz 1 3`	Disk IO bottlenecks	`iostat -xz 1 3`
11	`mpstat -P ALL 1 3`	Per-core CPU view	`mpstat -P ALL 1 3`
12	`uptime`	Check load average	`uptime`
13	`df -h`	Filesystem free space	`df -h`
14	`du -sh /var/log/* \| sort -h`	Find large log folders	`du -sh /var/log/* \| sort -h`
15	`find /var/log -type f -size +100M`	Find giant log files	`find /var/log -type f -size +100M`
16	`tail -f app.log`	Live follow logs	`tail -f app.log`
17	`tail -f app.log \| grep ERROR`	Live error stream	`tail -f app.log \| grep ERROR`
18	`grep -n ERROR app.log`	Find errors with line numbers	`grep -n ERROR app.log`
19	`grep -n 'Exception' big.log`	Find exceptions	`grep -n 'Exception' big.log`
20	`grep -A 20 -B 5 'Exception' app.log`	Show context around error	`grep -A 20 -B 5 'Exception' app.log`
21	`awk '/ERROR\|WARN/' app.log`	Filter with awk	`awk '/ERROR\|WARN/' app.log`
22	`sed -n '1000,1050p' app.log`	Print line range	`sed -n '1000,1050p' app.log`
23	`journalctl -u app -f`	Follow service logs	`journalctl -u app -f`
24	`journalctl -u app --since '1 hour ago'`	Recent service history	`journalctl -u app --since '1 hour ago'`
25	`systemctl status app`	Service state and recent logs	`systemctl status app`
26	`systemctl restart app`	Restart service	`systemctl restart app`
27	`curl -I http://localhost:8080`	Check HTTP response headers	`curl -I http://localhost:8080`
28	`curl -v http://localhost:8080/health`	Verbose HTTP check	`curl -v http://localhost:8080/health`
29	`ping -c 4 host`	Basic connectivity	`ping -c 4 host`
30	`traceroute host`	See network path	`traceroute host`
31	`nslookup host`	Basic DNS check	`nslookup host`
32	`dig host`	Detailed DNS query	`dig host`
33	`ip addr`	Check IP addresses	`ip addr`
34	`ip route`	Check routes	`ip route`
35	`hostname -I`	Quick host IP	`hostname -I`
36	`env \| sort`	Check environment variables	`env \| sort`
37	`echo $JAVA_HOME`	Check runtime config	`echo $JAVA_HOME`
38	`which java`	Check Java path	`which java`
39	`java -version`	Check Java version	`java -version`
40	`ulimit -a`	Check process limits	`ulimit -a`
41	`dmesg \| tail -50`	Kernel-level recent events	`dmesg \| tail -50`
42	`find /opt -name '*.jar'`	Find deployed jars	`find /opt -name '*.jar'`
43	`md5sum app.jar`	Verify file integrity	`md5sum app.jar`
44	`stat app.jar`	Verify size and modify time	`stat app.jar`
45	`docker ps`	Check containers	`docker ps`
46	`docker logs -f container`	Follow container logs	`docker logs -f container`
47	`docker inspect container`	Detailed container config	`docker inspect container`
48	`docker exec -it container sh`	Enter container shell	`docker exec -it container sh`
49	`git diff`	See config/code changes	`git diff`
50	`history \| tail -50`	Recent shell actions	`history \| tail -50`