After copying files, timestamps changed. How do I preserve them? Try: rsync -a --preserve-times /source/ /destination/ Info: rsync -a (archive mode) preserves modification timestamps (-t), permissions, ownership, and symbolic links. Adding --preserve-times explicitly ensures file modification times remain unchanged during the transfer. Examples: $ cp --preserve=timestamps file1 file2 # Preserve […]
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My server hits "too many open files" errors. Which process is the culprit? Try: sudo lsof | awk '{print $2}' | sort | uniq -c | sort -rn | head -10 Info: lsof lists open file descriptors across processes. Grouping the output by PID counts open handles and helps identify […]
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My server ran out of disk. Which files grew the most in the last 24 hours? Try: sudo find / -type f -mtime -1 -size +100M -exec ls -lah {} \; 2>/dev/null Info: Uses -mtime -1 to target files modified within the last 24 hours and -size +100M to isolate […]
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How do I set 644 for files and 755 for directories in one shot? Try: find /var/www/site -type d -exec chmod 755 {} + && find /var/www/site -type f -exec chmod 644 {} + Info: Uses -type d to grant directories execute permissions (755) and -type f to grant files […]
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Which network interface is being overloaded? Try: sar -n DEV 1 5 Info: sar -n DEV displays real-time network interface statistics. The 1 5 arguments sample network activity every 1 second for 5 samples, showing throughput such as rxkB/s and txkB/s, along with packet rates. Examples: $ sar -n TCP […]
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How do I see all differences between production and my feature branch? Try: git log --oneline --left-right --graph main...feature/new-api Info: The three-dot ... notation compares the two branches from their common ancestor. --left-right marks commits unique to the left branch with < and commits unique to the right branch with […]
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I need SSL for local development. How do I generate a certificate quickly? Try: openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -sha256 -days 365 -nodes -subj '/CN=localhost' Info: Generates a 4096-bit RSA self-signed certificate valid for 1 year. The -x509 option creates a self-signed certificate, while -subj supplies […]
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My high-priority process needs dedicated cores. How do I pin it to specific CPUs? Try: taskset -cp 0,1 3456 Info: taskset sets or retrieves CPU affinity. The -c option specifies CPU numbers, while -p applies the affinity to an existing process by PID. Examples: $ taskset -c 0-3 ./program # […]
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My logs are eating disk space. How do I compress old ones and keep only 30 days? Try: find /var/log/app -name '*.log' -mtime +7 -exec gzip {} \; && find /var/log/app -name '*.log.gz' -mtime +30 -delete Info: Compresses logs older than 7 days with gzip to save disk space, then […]
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Something is thrashing my disks. How do I see block-level filesystem activity live? Try: sudo btrace /dev/sda Info: btrace traces block-layer I/O events in real time. It shows low-level read and write activity along with timing, process IDs, and I/O stages, helping you identify which processes are generating disk activity. […]
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How do I find files changed within a specific time window for an incident report? Try: find /var/www -type f -newermt '2026-09-10 14:00:00' ! -newermt '2026-09-10 16:00:00' -printf '%TY-%Tm-%Td %TH:%TM %p\n' Info: -newermt filters files newer than a specified timestamp. Prefixing it with ! creates an upper time boundary, allowing […]
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My binary calls a function - which library actually provides it? Try: ltrace -e 'malloc+free' ls /tmp 2>&1 | head -20 Info: ltrace tracks dynamic library calls, similar to how strace tracks system calls. The -e option filters specific functions, showing arguments, return values, and dynamic library interactions. Examples: $ […]
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How do I run a task daily but with more control than cron? Try: sudo systemctl edit --force --full backup.timer Info: systemd timers provide a flexible alternative to cron with native logging through journalctl, dependency control, Persistent=true for missed runs, and RandomizedDelaySec to spread system load. Examples: $ systemctl list-timers […]
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How many active connections does my web server have right now? Try: sudo ss -tn state established '( sport = :80 )' | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -rn Info: ss -tn lists TCP connections using numeric addresses and ports. Filtering […]
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How do I split or extract pages from a PDF without a GUI? Try: pdftk input.pdf cat 5-10 output pages_5_to_10.pdf Info: pdftk manipulates PDFs from the command line. cat 5-10 extracts pages 5 through 10, while pdfinfo can inspect PDF metadata and page counts. Examples: $ pdftk file1.pdf file2.pdf cat […]
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Is my SSD really as fast as advertised? Try: sudo hdparm -Tt /dev/sda Info: hdparm -T measures cached RAM reads; -t benchmarks direct disk reads. dd can test sequential write performance using conv=fdatasync to flush cached writes. Examples: $ sudo hdparm -I /dev/sda | head -20 # Display drive specs […]
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