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 […]
Read More
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 […]
Read More
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 […]
Read More
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/ $ […]
Read More
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 […]
Read More
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 […]
Read More
Try: sudo tcpdump -i eth0 -w capture.pcap 'host 192.168.1.100 and port 80 and tcp[13] & 2 != 0' Info: tcpdump captures network packets with BPF filters. This example captures only SYN packets (TCP handshake start) to a specific host on port 80. Perfect for debugging network issues. Examples: $ sudo tcpdump […]
Read More
Try: systemd-cgls --unit=docker.service Info: systemd-cgls shows the cgroup tree with processes organized by their control groups. It is useful for understanding container isolation and process organization. Examples: $ systemd-cgls --unit=user.slice $ systemd-cgtop # Real-time cgroup resource usage $ cat /proc/1234/cgroup # Show cgroups for a specific PID Note: Use systemd-cgtop for […]
Read More
Try: sudo auditctl -w /etc/passwd -p wa -k passwd_changes Info: auditd is Linux's audit framework. auditctl sets up a watch on a file. You can then use ausearch later to query those logs. Examples: $ sudo auditctl -w /etc/shadow -p rwxa -k shadow_access $ sudo ausearch -k passwd_changes -ts today $ […]
Read More
Try: find /images -name '*.jpg' | parallel -j+0 'convert {} -resize 800x600 {}.resized' Info: GNU parallel executes commands in parallel across all CPU cores. Dramatically speeds up batch processing of files, downloads, or any repeatable task. Examples: $ parallel -j 4 gzip ::: *.log $ cat urls.txt | parallel -j 10 […]
Read More
Try: lsof -p 3456 Info: lsof shows all files, sockets, and connections used by a process. Great for troubleshooting. Examples: $ lsof -p 3456 $ lsof -i :8080 $ lsof -u username Note: Use -i for network connections. -i :PORT shows the process using that port. LinuxTeck.com linuxteck@ubuntu:~$ lsof -p 3456 […]
Read More
Try: crontab -e Info: crontab -e opens the editor for scheduled tasks. Format: minute hour day month weekday command. Examples: $ crontab -e $ crontab -l $ crontab -r Note: Use journalctl -u cron to inspect active execution logs. Always use full path variables in your commands. LinuxTeck.com linuxteck@ubuntu:~$ crontab -e […]
Read More
Try: time ./backup.sh Info: The time command shows execution time. real is wall clock time, user is CPU time for the program, and sys is CPU time for system calls. Examples: $ time ./deploy.sh $ /usr/bin/time -v ./process.py $ time tar -czf backup.tar.gz /home/data Note: Use /usr/bin/time -v for detailed resource […]
Read More
Try: rsync -avz --delete /source/ /destination/ Info: rsync only transfers changed files, making backups much faster. -a means archive, -v means verbose, and -z enables compression. Examples: $ rsync -avz /home/user/ /mnt/backup/ $ rsync -avz --delete remote:/data/ /local/backup/ $ rsync -avz --exclude='*.tmp' /src/ /dst/ Note: Use --dry-run first. A trailing slash […]
Read More
Try: sudo find /var/log -name '*.log' -mtime +30 -delete Info: Delete log files older than 30 days. The -mtime +30 finds files modified more than 30 days ago. Use sudo because /var/log files are owned by root. Examples: $ sudo find /var/log -name '*.log' -mtime +30 -delete $ find ~/Downloads -type […]
Read More
Try: tail -20 /var/log/syslog Info: The tail command shows the last lines of a file without loading the entire content into memory. It's perfect for checking recent log entries. LinuxTeck.com linuxteck@ubuntu:~$ tail -20 /var/log/syslog Jun 26 11:52:27+0530 DEBUG reviving: failed for 'baseos', mismatched repomd. Jun 26 11:52:27+0530 DEBUG repo: downloading from […]
Read More