RH124

• Linux

Linux Help

<aside> 🧩 Linux help

• man pages

  • 9 cat

• man - K “keyword”

  • ⇒ when we are not aware about exact command, we can search in man page using this command

• whatis

  • ⇒ complete command is required
  • exact command and short description

• apropos

  • ⇒ if we dont know the full command it will help

• info

• which

  • path of executables

• whereis

  • path of executable + path of documentation

• updatedb and then mandb ⇒ this is required to get updated

• man man → help to identify the man page number of the specified tasks.

• Navigate man pages :

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<aside> 🔑 Input, Output, Errors

• Input [stdinput = 0]
  • Keyboard
  • File
  • Pipe “|”
  • eg: ls, pwd, “<” → input redirection operator
• Output [stdout = 1]
  • Terminal
  • File
  • eg: “>” → overwrite redirection operator ”>>” → append redirection operator
• Errors [stderr = 2]
  • File
  • terminal
  • eg: 2>/dev/nul
  • eg: find / -name awad.txt ⇒ many permission denied errors are coming so in order to print only the wanted message and sort out the errors we can use the following ⇒ find / -name awad.txt 2>/dev/null → null directory does not stores any data and discards all the unwanted data/errors OR ⇒ find / -name awad.txt 2>>red.txt → the errors will be stores in a file named red.txt

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<aside> 🔑 Text Editors

• Vi / Vim editor
  • Vimtutor → guide of vim editor and study all command
• Nano editor
• Gedit editor </aside>

<aside> 🔑 Variable [VERY IMPORTANT]

• Local Var

  • Limited to the termninal

• Env Var [Environment Variable]

  • All the terminals associated with the user profile

  • set the value of environment var=awadesh

  • to unset ⇒ unset var

  • push paticular variable ⇒ export var

  • editng the profile file and make it permanent

    → ls -a

    → vi .bash_profile

    → export var=”awadesh RHCSA” → save the file.

    → restart the system

  → echo $var

  Controlling the setting of how we can change the environment setting

  set | less

  echo $PS1

  PS1=”<path_of_PS1>” ⇒ PS1=””

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<aside> 🔑 User Management

• 3 categories

  • root user
    • known as super-user
    • ID = 0
  • normal user
  • service user

• eg: awad : x : 1000: 1000: awad: / home/ awad: /bin/bash

• Shadow file → /etc/shadow

• /etc/group

• useradd lpu2 → adding user

• usermod -u 5000 lpu2 → changing the user id

• usermod -g 1001 lpu2 → changing group name

• tail -l /etc/passwd →

• usermod -s /bin/sh awadesh → changing the shell

• userdel lpu10 → delete the user

• userdel -r lpu10 → delete user with home directory

• pwunconv → disables the shadow file and the password which used to go to the shadow file will be visble along with the passwd file

• pwconv → enables shadow file

• UID Ranges :

getent → get all the members details

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