Try: ss -ti | grep -A3 'ESTAB' | head -20 Info: ss -ti dumps TCP internal metrics. Look for retrans:X/Y (X current retransmits, Y total) and rtt (round-trip time). Non-zero retransmits signal packet loss or network congestion. Examples: $ ss -ti state established '( dport = :443 )' # Inspect HTTPS […]
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Try: sed -n '/BEGIN CERTIFICATE/,/END CERTIFICATE/p' /etc/ssl/certs/server.crt Info: sed -n suppresses automatic printing. The pattern '/START/,/END/p' prints all lines between two matching delimiters (inclusive). Examples: $ sed -n '/^\[database\]/,/^$/p' config.ini # Extract section until empty line $ awk '/BEGIN/,/END/' file.txt # Equivalent using awk $ sed -n '/ERROR/,+5p' logfile # Print […]
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Try: ./deploy.sh 2>&1 | tee -a deploy.log Info: tee splits stdout to both terminal and file. 2>&1 redirects stderr into stdout first to capture error logs. -a appends output instead of overwriting. Examples: $ ./script.sh 2>&1 | tee output.log # Overwrite log with output + errors $ make 2>&1 | tee […]
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Try: find /home/linuxteck -type f -exec md5sum {} + | sort | uniq -w32 -D Info: md5sum hashes file contents, sort groups identical hashes, and uniq -w32 -D compares the 32-character hash to output all duplicate files. Examples: $ find . -type f -exec md5sum {} + | sort | uniq […]
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Try: find /var/www -type f -newermt '2026-07-23 14:00:00' ! -newermt '2026-07-23 16:00:00' Info: -newermt 'DATE' matches files modified AFTER a timestamp. Combined with ! -newermt, it isolates files modified BETWEEN two specific times, making it useful for forensic analysis. Examples: $ find / -newermt '1 hour ago' -type f 2>/dev/null # […]
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Try: ssh -L 3307:db-internal:3306 -N -f linuxteck@jumphost Info: -L local_port:target_host:target_port forwards local traffic through SSH to a remote server. -N skips the remote shell, and -f sends SSH to the background. Examples: $ ssh -L 8080:localhost:80 user@server # Access remote web app locally $ ssh -R 9000:localhost:9000 user@server # Expose local […]
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Try: sudo systemctl edit --force --full myapp.service Info: Restart=on-failure restarts the app after a non-zero exit or crash, while RestartSec adds a delay before restarting. StartLimitBurst and StartLimitIntervalSec help prevent a service from repeatedly restarting in a crash loop. Examples: $ sudo systemctl status myapp # View service status $ sudo […]
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Try: ionice -c 3 -p $$ Info: ionice sets I/O priority. Class 3 (idle) only allows disk access when no other process needs it. Examples: $ ionice -c 3 nice -n 19 rsync -av /src /dst # Throttles CPU + I/O $ ionice -c 2 -n 7 tar -czf backup.tar.gz /data […]
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Try: mtr -rw -c 20 google.com Info: mtr combines traceroute and ping. -r enables report mode, -w shows full hostnames, and -c 20 sends 20 pings per hop. Examples: $ mtr google.com # Interactive real-time mode $ mtr --tcp -P 443 google.com # TCP mode on port 443 $ mtr -j […]
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Try: ssh-keygen -t ed25519 -a 100 -f ~/.ssh/id_ed25519 -C "linuxteck@ubuntu-2026" Info: Ed25519 provides faster, more secure keys than RSA. -a 100 increases KDF rounds to strengthen passphrase protection against offline brute-forcing. Examples: $ ssh-copy-id -i ~/.ssh/id_ed25519.pub user@server # Copy public key to server $ ssh-keygen -y -f ~/.ssh/id_ed25519 # Print public […]
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Try: iperf3 -c 192.168.1.100 Info: iperf3 measures real TCP/UDP throughput. Run iperf3 -s on the server and iperf3 -c <SERVER_IP> on the client. Examples: $ iperf3 -s # Server mode (run first) $ iperf3 -c server -u -b 1G # UDP test at 1 Gbps $ iperf3 -c server -R # […]
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Try: openssl enc -aes-256-cbc -pbkdf2 -in secrets.txt -out secrets.enc Info: AES-256-CBC provides strong symmetric encryption. -pbkdf2 uses secure key derivation (automatically adding a salt) to prevent brute-force attacks. Examples: $ openssl enc -d -aes-256-cbc -pbkdf2 -in secrets.enc -out secrets.txt # Decrypt $ tar -czf - /home/data | openssl enc -aes-256-cbc -pbkdf2 […]
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Try: w linuxteck Info: w <user> lists active sessions and current commands; ps -u <user> lists all running processes. Examples: $ w # View all logged-in users $ last linuxteck | head # Check recent login history $ lslogins linuxteck # User account details and password policy Note: w displays IDLE […]
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Try: sudo du -h -d 1 / 2>/dev/null | sort -rh | head -10 Info: du -h -d 1 scans top-level directory sizes. sort -rh ranks the largest directories first, and 2>/dev/null silences permission errors. Examples: $ sudo du -h -d 2 /var | sort -rh | head -20 $ ncdu […]
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Try: tail -f /var/log/nginx/error.log | grep --line-buffered -E --color=always 'error|warn|critical|$' Info: --color=always highlights matching text. The |$ pattern matches every line so non-matching lines still display. --line-buffered ensures real-time output. Examples: $ tail -f app.log | grep --line-buffered --color=always -E 'ERROR|WARN|$' $ journalctl -f | grep --line-buffered --color=always -E 'Failed|Error|$' $ […]
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Try: ps -eo pid,ppid,stat,cmd | awk '$3 ~ /Z/' Info: Zombies have STAT=Z and are already-dead processes waiting for their parent to reap them. You cannot kill a zombie directly. Send SIGCHLD to its parent process (PPID) to prompt it to reap the child. Examples: $ ps aux | grep defunct […]
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