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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I need to reach server-C through server-A and server-B. Any shortcut? Try: ssh -J linuxteck@bastion,linuxteck@jumphost linuxteck@internal-server Info: -J (Jump host) chains multiple SSH connections sequentially: local → bastion → jumphost → target. This lets you reach an internal server through multiple intermediate SSH hosts without manually opening nested SSH sessions. […]
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Try: sudo iotop -aoP -d 5 Info: iotop tracks real-time disk I/O. -a accumulates total I/O since start, -o filters active processes, and -P groups activity by process instead of thread. Examples: $ sudo iotop -o # Show only processes actively performing I/O $ sudo iotop -b -n 5 > iotop.log […]
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A binary is failing with "undefined symbol". How do I check what a .so file exports? Try: nm -D /usr/lib/x86_64-linux-gnu/libssl.so.3 | grep ' T ' | head -20 Info: nm -D displays the dynamic symbols available in a shared library. The T symbol type indicates a function defined in the […]
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How do I quickly grab a value from JSON output on the command line? Try: curl -s https://api.github.com/users/torvalds | jq -r '.name, .public_repos, .followers' Info: jq is a powerful command-line JSON processor. The -r option outputs strings without quotes, while jq filters can extract, filter, map, and transform JSON data. […]
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Try: pkill -f 'python.*worker.py' Info: pkill matches processes using a pattern. The -f option matches against the full command line, making it useful when multiple processes run the same script with different arguments. Always preview matching processes with pgrep -af before terminating them. Examples: $ pgrep -af 'ffmpeg' # Preview matching […]
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Try: rsync -avz --bwlimit=5000 /source/ linuxteck@backup:/dest/ Info: --bwlimit=5000 limits rsync's transfer rate to about 5,000 KB/s, helping prevent large file transfers from consuming all available network bandwidth. Examples: $ rsync -avz --bwlimit=10M /src/ user@host:/dst/ # Limit to 10 MB/s $ scp -l 40000 file.iso user@host: # Limit SCP bandwidth in Kbit/s […]
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Try: inotifywait -m -r -e create,modify,delete,move --timefmt '%Y-%m-%d %H:%M:%S' --format '%T %w%f %e' /var/www Info: inotifywait uses Linux kernel APIs for efficient file monitoring. -m runs continuously, -r recurses through subdirectories, and -e filters the specified events. Examples: $ inotifywait -m -e close_write /uploads | while read path event file; do […]
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Try: sudo find / -inum 524290 2>/dev/null Info: Every file has a unique inode per filesystem. Running find -inum locates all directory entries pointing to that specific inode number. Examples: $ find / -inum 524290 2>/dev/null # Find file by inode number $ ls -i file.txt # Display inode number for […]
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