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트러블슈팅 가이드17
Diagnosing TIME_WAIT Socket Exhaustion — TCP Connection States and Kernel Tuning
Why TIME_WAIT exists in the TCP state machine, how to diagnose it with ss, its relationship to ephemeral port exhaustion, tcp_tw_reuse vs. the removed tcp_tw_recycle, and SO_REUSEADDR—covered accurately for practitioners.
Diagnosing Kubernetes Pod CrashLoopBackOff — Complete Fixes by Cause
Understand what CrashLoopBackOff actually means and how backoff works, then walk through a systematic diagnosis and fix for each cause—exit codes, logs, probes, OOMKilled, missing config, and more.
Zombie Processes · OOM Killer — Diagnosis and Prevention
Covers why zombie processes appear and how to find the parent to clean them up, plus how to detect, prevent, and tune OOM Killer priority, and how to cap memory with cgroups.
Diagnosing DNS Resolution Errors — nslookup · dig · systemd-resolved
How to diagnose and fix DNS issues such as lookup failures, cache pollution, and incorrect nameserver configuration using nslookup, dig, host, and systemd-resolved.
Diagnosing I/O Bottlenecks — iostat · iotop · blktrace
Learn how to check disk I/O utilization with iostat, find I/O-heavy processes with iotop, and measure storage performance with blktrace and fio.
Diagnosing Network Packet Loss — ping · mtr · tcpdump
How to confirm packet loss with ping, locate the hop where it occurs with mtr, and capture live packets with tcpdump to analyze retransmissions and errors.
Memory Leak Diagnosis — /proc/meminfo · smaps · valgrind
Covers how to assess memory status with /proc/meminfo and free, analyze process memory with smaps and pmap, and find leaks with Valgrind and AddressSanitizer.
CPU Overload Diagnosis — top · htop · perf · uptime
How to pinpoint CPU-heavy processes with top/htop, check load trends with uptime/vmstat, and find bottleneck causes with perf and strace.
Completely Fix git push rejected — non-fast-forward · protected branch · pre-receive hook
A guide to identifying the cause of each git push failure type—Updates were rejected, remote rejected, pre-receive hook declined, and more—and resolving it safely.
Too many open files — Fixing ulimit File Descriptor Limits
A guide to resolving file descriptor limit errors such as EMFILE: too many open files and accept4() failed (24: Too many open files) using ulimit, limits.conf, and systemd LimitNOFILE.
Fixing SSL Certificate Expiry and Renewal Failures — A Complete Guide to certbot renew Errors
A step-by-step guide to resolving Let's Encrypt SSL certificate renewal errors, including NET::ERR_CERT_DATE_INVALID, certbot renew failures, a blocked port 80, and Nginx reload failures.
When Docker Containers Keep Restarting — Causes and Fixes by Exit Code
A guide to diagnosing and fixing containers that repeatedly show Restarting or Exited in docker ps by checking logs, exit codes, and the restart policy.
Completely Fixing MySQL/MariaDB Connection Errors — ERROR 1045 · Can't connect · socket
Causes and fixes for MySQL/MariaDB connection errors by type, including ERROR 1045 (28000): Access denied, Can't connect to MySQL server on localhost, and a missing socket file.
Address already in use — Finding and resolving port conflicts
When you hit a bind: address already in use error, use ss, lsof, and fuser to identify the process occupying the port, then free it safely or change the port.
Linux Disk Full — Fix "No space left on device" in 10 Minutes
When a "No space left on device" error appears, this guide shows how to find the culprit in 10 minutes with df, du, and find, then safely clean logs, Docker, package caches, and large files.
Fixing Nginx 502 Bad Gateway: Causes by Log Message and Inspection Order
Diagnose Nginx 502 Bad Gateway from error.log. Separate connection refused, PHP-FPM socket and permission issues, upstream connection closures, and oversized header errors, then walk through the fix and verification.
SSH Connection Error Troubleshooting Guide (Connection refused, Permission denied, etc.)
A troubleshooting guide to quickly pinpoint causes and fix SSH connection errors by type, including Connection refused and Permission denied (publickey).