Master Java Server Troubleshooting: CPU, Memory, Disk, GC & Network Issues

CPU

Start by checking CPU anomalies, which are often easier to locate. Common causes include business logic loops, frequent GC, and excessive context switches. Use ps to find the process ID, then top -H -p pid to identify high‑CPU threads, convert the thread ID to hex with

printf '%x
' pid

, and locate the stack with jstack pid | grep 'nid' -C5 --color. Analyze WAITING and TIMED_WAITING sections in the stack trace. For a broader view, run:

cat jstack.log | grep "java.lang.Thread.State" | sort -nr | uniq -c

Disk

Check disk space using df -hl. For performance issues, run iostat -d -k -x to see utilization and I/O rates. Identify the responsible process with iotop, then map a thread ID to a PID via readlink -f /proc/*/task/tid/../... Examine detailed I/O with cat /proc/pid/io and list open files using lsof -p pid.

Memory

Begin with free to assess overall memory. Common OOM errors include unable to create new native thread , Java heap space , and Meta space . Use jmap -dump:format=b,file=heap.hprof pid and analyze the dump with MAT (Memory Analyzer Tool). Enable automatic heap dumps with -XX:+HeapDumpOnOutOfMemoryError. For native memory, activate -XX:NativeMemoryTracking=summary or detail and run jcmd pid VM.native_memory baseline, later compare with jcmd pid VM.native_memory detail.diff. Track allocations via strace -f -e "brk,mmap,munmap" -p pid.

GC Issues

Use jstat -gc pid 1000 to monitor GC generations. Enable detailed GC logging with

-verbose:gc -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintGCTimeStamps

. Frequent young GC may require tuning -Xmn or -XX:SurvivorRatio. Full GC triggers include concurrent phase failures, promotion failures, large object allocation failures, or explicit System.gc(). Dump heap on GC events with -XX:HeapDumpPath and inspect using jinfo.

Network

Network problems often manifest as timeouts. Distinguish between connection timeout and read/write timeout, and ensure client timeouts are shorter than server timeouts. Diagnose TCP queue overflows with netstat -s | egrep "listen|LISTEN" and ss -lnt. Monitor RST packets using tcpdump and analyze with Wireshark. Manage TIME_WAIT and CLOSE_WAIT states; reuse and recycle TIME_WAIT sockets via sysctl settings net.ipv4.tcp_tw_reuse=1 and net.ipv4.tcp_tw_recycle=1, and adjust tcp_max_tw_buckets if necessary.