Linux commands

Viewing files

  • cat a.txt full content
  • more a.txt page by page, forward only
  • less a.txt page by page, both directions
  • head -n 5 a.txt top 5 lines
  • tail -n 5 a.txt bottom 5 lines
  • history all used commands
  • !2 execute 2nd command from history
  • whoami active user

System info

  • hostnamectl OS version & details
  • dpkg --print-architecture system arch (amd64, arm64)
  • lsb_release -a or cat /etc/*release or cat /etc/issue* or cat /proc/version
  • uname -a system name & arch
  • uname -m arch type (amd or arm)
  • hostname -I ip address

Resource usage

  • du -sh folder_or_file size (s-summary h-human readable)
  • lscpu | grep MHz processor speed
  • top running processes
  • df disk space
  • sudo fdisk -l all disk space
  • free -m / free -g free ram in MB/GB
  • ps ux all processes & command path
  • pidof programName pid (may return multiple)

Permissions

  • u user, g group, o other, a all
  • chmod u=rwx fileName set user read/write/execute
  • chmod g+w fileName add group write
  • chmod o-x fileName remove other execute
  • chmod -R o=rwx folder recursive (uppercase -R)
  • ln -sf path_to_source path_to_target works for files and folders
  • target shouldn’t exist, else it’s overridden (due to -f)
  • if creation fails, try with sudo

find / search

  • find / -name "hello.js"
  • lsof -i -P -n | grep LISTEN listening processes
  • rm -fr folder force delete

Custom domain

  • add in /etc/hosts (prefer over /etc/domain)
    • eg: 127.0.0.1 ravinder.com

External hard disk (ntfs)

  • check file system: sudo blkid /dev/sda1
  • install utility if ntfs: sudo apt-get install ntfs-3g
  • create folder: sudo mkdir -p /home/ravinder/2.0TB
  • mount: sudo mount -t ntfs-3g /dev/sda1 /home/ravinder/2.0TB

gsettings

  • for GUI-less settings: gsettings or dconf
  • ref: http://manpages.ubuntu.com/manpages/precise/en/man1/gsettings.1.html