lsof Command on Linux: Find Process Using a Port or File
Use lsof on Linux: list open files and sockets, lsof -i :PORT, who blocks umount, deleted files still…
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No Space Left on Device on Linux: df, du, Logs, Docker and Inodes
Fix Linux no space left on device: df -h and df -i, du under /var, journalctl vacuum, large…
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dig and nslookup on Linux: DNS Troubleshooting (A, MX, TTL, resolvers)
Troubleshoot DNS on Linux with dig and nslookup: read resolv.conf, query A/MX records, +trace, test against 8.8.8.8, NXDOMAIN…
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Linux Out of Memory (OOM): Find the Killer, Fix and Prevent Recurrence
Fix Linux out of memory: read OOM killer in dmesg/journalctl, use free and htop, systemd MemoryMax, swap as…
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systemd Service Failed to Start? Troubleshooting Guide for Linux
Fix systemd service failed to start: systemctl status, journalctl -u, ExecStart path and permissions, User=, dependencies, daemon-reload, and…
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Nginx 502 Bad Gateway: Causes and Fixes on Linux (Upstream, PHP-FPM, Timeouts)
Fix Nginx 502 Bad Gateway on Linux: check upstream is running, proxy_pass and fastcgi_pass, error.log messages, PHP-FPM pools,…
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ss Command on Linux: Listening Ports, Connections and Troubleshooting
Use ss on Linux instead of netstat: list listening TCP/UDP ports, show established connections, map sockets to PIDs,…
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chrony Not Syncing? Troubleshooting Time Sync on Linux
Fix chrony not syncing on Linux: read Not synchronised, 506 and 0 sources online errors, check the daemon,…
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Linux Performance Troubleshooting: top, iostat, vmstat Explained
Diagnose Linux performance problems with top, vmstat, and iostat: read load average, identify CPU vs I/O vs memory…
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Fix “Extension Not Found in Context” Dialplan Error in ViciDial/Asterisk
Fix the Asterisk error 'extension not found in context' (often seen on inbound trunks like trunkinbound) by locating…
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