* ps / -A / fax / auxww
* top / htop / atop 2
* pgrep -x
* pstree -p (parent/child/fork)
* background/forground:  & ctrl-z jobs bg fg
* kill -KILL / killall / man signal / SIGTERM , SIGKILL , SIGHUP, SIGINT
* lsof -n / list open files
* /proc , cmdline , cwd , exe , loginuid , fd , environ
       cat /proc/uptime
       cat /proc/version
       cat /proc/swaps
       cat /proc/partitions
       cat /proc/cpuinfo
* ps -p 1 -o comm=

* df -hT
* du -hscS
* ncdu / gdu
* fdisk / gdisk
* mount / umount / eject , (cdrom, usb) , fstab
* dd / Duplicating Disks
      dd if=/dev/zero of=/test.fs bs=1M count=8192 status=progress
      mkfs.ext4 /test.fs
      mount -o loop /test.fs /disk
      df -hT | grep disk
      losetup --list /dev/loop6
      losetup --list --noheadings -O BACK-FILE /dev/loop6
      cat /sys/block/loop6/loop/backing_file
      
      dd if=/dev/zero of=/swap.fs bs=1M count=8192 status=progress
      chown root:root /swap.fs
      chmod 0600 /swap.fs
      mkswap /swap.fs
      swapon /swap.fs
      swapon --show
      free -h
      grep -i --color swap /proc/meminfo
      
      #/etc/fstab
      /swap.fs swap swap defaults 0 0
      /test.fs /disk ext4 defaults 0 1

* ls -lh /dev/disk/by-uuid/
* blkid /dev/sda1
* lsblk -p