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 […]
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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 […]
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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 […]
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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 # […]
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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 […]
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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. […]
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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 […]
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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/ […]
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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 […]
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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 […]
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Try: cat >> ~/.ssh/config << 'EOF' Host * ControlMaster auto ControlPath ~/.ssh/cm-%r@%h:%p ControlPersist 10m EOF Info: SSH multiplexing reuses the first connection for subsequent sessions. ControlMaster creates a master socket, while ControlPersist keeps it alive for 10 minutes. Examples: $ ssh -O check user@server # Verify master exists $ ssh -O […]
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Try: time find /tmp/cache -type f -name '*.tmp' -print0 | xargs -0 -n 100 -P 8 rm Info: -print0 outputs null-separated filenames. -0 tells xargs to expect them. -n 100 batches 100 files per rm call. -P 8 runs 8 parallel processes. Examples: $ find /var/log -name '*.gz' -mtime +30 -print0 […]
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Try: sudo mount --bind /var/www/site /home/linuxteck/website Info: Bind mounts make the same content visible at multiple paths. No copying, no symlinks. Both paths refer to the same underlying files. Examples: $ sudo mount --bind /source /destination $ sudo mount --bind -o ro /etc /backup/etc_ro # Read-only bind $ sudo umount /home/linuxteck/website […]
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Try: sudo ls -la /proc/1234/fd/ Info: Linux keeps deleted files on disk while any process has them open. /proc/PID/fd/ shows file descriptors with the (deleted) marker for such files. Copy from there to recover. Examples: $ sudo lsof +L1 # Find all deleted-but-open files $ sudo ls -la /proc/$(pgrep nginx)/fd/ $ […]
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Try: watch -n 5 'ps -eo pid,user,vsz,rss,comm --sort=-rss | head -20' Info: watch runs the command repeatedly, showing memory trends. RSS shows physical memory in KB. If a process's RSS keeps growing, you have a leak. Examples: $ watch -n 1 'free -m' $ smem -tk -s rss # More accurate […]
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Try: sudo gdb -p 1234 -batch -ex 'thread apply all bt' -ex 'quit' Info: gdb can attach to running processes and dump stack traces without stopping them. Essential for debugging production issues where you cannot restart the service. Examples: $ sudo gdb -p $(pgrep nginx) -batch -ex 'bt' $ sudo strace […]
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