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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How do I save errors and normal output to different files? Try: ./deploy.sh > success.log 2> errors.log Info: > redirects stdout (file descriptor 1), while 2> redirects stderr (file descriptor 2). Separating the two streams keeps normal output and error messages in different files for easier troubleshooting. Examples: $ ./script […]
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How do I see all child processes spawned by a parent? Try: pstree -pau 3456 Info: pstree displays process hierarchies. -p includes PIDs, -a shows full command arguments, and -u lists usernames. Curly braces {} indicate threads. Examples: $ pstree -pau $$ # View process tree starting from current shell […]
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How do I write an ISO to a USB stick from the command line? Try: sudo dd if=ubuntu-24.04.iso of=/dev/sdb bs=4M status=progress conv=fsync Info: dd writes data as raw blocks. bs=4M uses 4 MiB blocks for efficient transfers, status=progress displays live transfer progress, and conv=fsync waits for the data to be […]
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Try: sudo grep 'Failed password' /var/log/auth.log | awk '{print $11}' | sort | uniq -c | sort -rn | head -5 Info: This command searches /var/log/auth.log for failed SSH authentication attempts, extracts the source IP address with awk, counts occurrences with uniq -c, and sorts the results to show the most […]
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My laptop is slow - is it thermal throttling? Try: watch -n 1 'grep MHz /proc/cpuinfo | sort -u; sensors | grep -E "Core|Package"' Info: CPU clock speeds can drop when temperatures reach thermal limits. sensors displays live hardware temperatures, while the CPU frequency output shows current clock speeds. Low […]
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Which files on my server haven't been touched in over a year? Try: sudo find /home -type f -atime +365 -printf '%T@ %p\n' | sort -n | head -20 Info: -atime +365 filters files that have not been accessed in over a year. -printf '%T@ %p\n' adds a numeric timestamp […]
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How do I dump a MySQL database while it's serving traffic? Try: mysqldump --single-transaction --quick --lock-tables=false --routines --triggers --events -u backup -p production_db | gzip > backup_$(date +%Y%m%d).sql.gz Info: --single-transaction creates a consistent snapshot without locking tables for InnoDB. --quick streams rows instead of loading the entire result into memory, […]
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How do I check when a file was last read without changing that timestamp? Try: stat -c '%n Access: %x Modify: %y Change: %z' /var/log/syslog Info: stat with -c custom formatting lets you inspect a file's timestamps without reading its contents like cat would. The format specifiers %x show access […]
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My bash script has a memory leak somewhere. How do I profile it? Try: /usr/bin/time -v bash ./my_script.sh 2>&1 | grep -E 'Maximum|CPU|Elapsed|Voluntary' Info: /usr/bin/time (GNU binary, not the shell builtin) with -v tracks detailed resource usage. Peak memory usage is shown under Maximum resident set size (Maximum RSS). Examples: […]
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