public/subjects/login/README.md

login

In the movie TRON: Legacy, Linux is rebranded "SolarOS" in reference to Solaris, another Unix OS

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Start the VM to boot the previously installed Debian system.

Do the following for both a user and the superuser (root) :

• Log in
• Clear the console using the keyboard shortcut
• Change the password to a space : " "
• Show the command history using five keystrokes or less (using autocompletion)
• Log out using the keyboard shortcut

Just numbers

Login as root on the third Linux console.

Check the Internet connectivity with the command ping google.com. After a few hops, interrupt the program with : Ctrl + C.

Behind every name in a computer system there is a number (ID, index, address, etc) :

• User identifier
  • root → 0
  • student → 1000
• IP address
  • google.com → 216.58.214.14 (quad-dotted notation) → 3627734542
  • tencent.com → 117.169.101.44 (quad-dotted notation) → 1974035756
• File inode
  • /etc/fstab → 44696029
  • .profile → 59639363
• Port
  • HTTP → 80
  • HTTPS → 443
• Process identifier
  • cron → 254

Names exist because they are human readable, but behind the scenes they are converted into numbers, unique in their namespace :

• A domain name can have several IP addresses, but an IP address can only identify one domain name
• Several processes may have the same name, but a PID identifies a single process

Find the commands to get :

• the inode of a specific file
• the current user ID
• the PID of a program, for example bash