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 […]
Read More
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 […]
Read More
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|$' $ […]
Read More
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 […]
Read More
Try: zgrep 'ERROR' /var/log/app-2026-06.log.gz Info: zgrep, zcat, and zless inspect .gz files in memory without extracting them to disk. Examples: $ zcat access.log.gz | awk '{print $1}' | sort -u $ zless huge-log.log.gz # Page through compressed file $ find /var/log -name '*.log' -mtime +7 -exec gzip {} \; Note: z-tools […]
Read More
Try: history | grep -E 'sed.*i.*g' | tail -10 Info: history outputs numbered past commands. Combining it with grep -E (regex) lets you locate specific command patterns fast. Execute entry 892 with !892. Examples: $ history | grep 'docker run' # Find docker commands $ history | awk '{print $2}' | […]
Read More
Try: sudo lsof -iTCP:3306 -sTCP:ESTABLISHED Info: lsof -iTCP:PORT lists active network connections on a port. -sTCP:ESTABLISHED filters out listening sockets to show active connections only. Examples: $ sudo lsof -iTCP:80 -sTCP:LISTEN # Active listeners on port 80 $ sudo lsof -i @192.168.1.100 # Filter by remote IP $ sudo lsof -Pn […]
Read More
Try: rsync -avz --checksum --delete /var/www/ linuxteck@backup:/var/www/ Info: --checksum compares file contents rather than timestamps to catch true changes. --delete removes destination files that no longer exist on the source. Examples: $ rsync -avz --dry-run /src/ user@host:/dst/ # Dry-run preview $ rsync -avz --exclude='*.log' --exclude='cache/' /src/ /dst/ $ rsync -avz --link-dest=/prev/backup […]
Read More
Try: strace -c -f ./slow_script.sh Info: strace -c summarizes system calls by total time spent. -f follows child processes. The summary helps reveal which system calls are consuming the most time. Examples: $ strace -c ls -la /usr $ strace -c -f -p 1234 # Profile a running PID $ strace […]
Read More
Try: rename 's/IMG_(\d+)\.jpg/photo_$1.jpg/' *.jpg Info: The Perl rename command uses regex to rename files in bulk. -n is a dry-run option that shows what would change without actually renaming files. Examples: $ rename -n 's/\.jpeg$/\.jpg/' *.jpeg # Dry-run preview $ rename 'y/A-Z/a-z/' *.TXT # Lowercase extension/file $ rename 's/(.+)/prefix_$1/' *.log # […]
Read More
Try: systemd-run --scope -p CPUQuota=25% -p MemoryMax=500M ./heavy_script.sh Info: systemd-run creates a transient cgroup with resource limits. Any process launched inside respects those limits. Great for testing or running untrusted code. Examples: $ systemd-run --scope -p CPUQuota=50% stress --cpu 8 $ systemd-run --user -p MemoryMax=1G firefox $ systemd-run --scope -p IOWeight=10 […]
Read More
Try: sudo lsof +D /mnt/backup Info: Lists all active processes holding open files under a specific directory to identify unmount blockers. Examples: $ sudo lsof +D /mnt/usb $ sudo fuser -m /var/log # List processes using filesystem $ sudo fuser -k -SIGTERM /mnt/backup # Graceful kill first Note: +D recurses subdirectories. […]
Read More
Try: TMPFILE=$(mktemp) && trap 'rm -f "$TMPFILE"' EXIT INT TERM Info: mktemp creates a secure, unique file; trap catches signals like exit or Ctrl+C to guarantee cleanup. Examples: $ TMPDIR=$(mktemp -d) # Secure temp directory $ trap 'rm -rf "$TMPDIR"' EXIT $ mktemp -t script-XXXXXX.log # Custom prefix Note: Prevents dangling […]
Read More
Try: ss -tn state established | awk 'NR>1 {split($3,a,":"); print a[1]}' | sort -u Info: First run ss to see the raw output, then use awk to parse it. split($3,a,":") splits IP:PORT into array a. NR>1 skips the header line. Examples: $ ip -4 addr | awk '/inet / && !/127.0/ […]
Read More
Try: sudo inotifywait -m -e modify /etc/nginx/nginx.conf Info: inotifywait monitors filesystem events using the Linux inotify kernel API. The -m option keeps it running in monitor mode. Examples: $ inotifywait -m -e modify /etc/nginx/nginx.conf | while read; do systemctl reload nginx; done $ inotifywait -m -r -e create /var/incoming | while […]
Read More
Try: diff <(cd /source && find . -type f -exec md5sum {} + | sort) <(cd /backup && find . -type f -exec md5sum {} + | sort) Info: Combines find, md5sum, sort, and process substitution to compare directories by content, not just names. Detects even single-byte modifications. Examples: $ rsync […]
Read More