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linux-cheat-sheat.md

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Linux Cheat Sheat

Create new user:

  • **useradd -m **username
    • -m creates a home directory for the user
  • passwd username
  • **usermod -a -G sudo **username
    • to add user to group, e.g. sudo
  • **chsh -s /bin/bash **username
    • specify shell for a user?

Installing packets for Debian and Ubuntu based systems:

**apt-get install **pkg

Useful cmds:

  • **uname -a **- kernel info
  • ifconfig/ ip addr show - network informationq
  • **netstat/ lsof -i - **info about ports/routing
  • **df **- (disk free )display disk space
  • **systemctl - **info about running services
  • du - disk usage
  • **top/htop/ps - **display CPU usage/precesses
  • **ls /mnt - **list mounted devices
  • **mount - **show existing mounts
    • e.g **mount /dev/sda2 /mnt - **mount sda2 device to /mnt
  • **less /etc/fstab - **boot device list

4 command types:

  1. ** An executable command**
  2. A command built in into the shell
  3. A shell function
  4. An Alias
  • **type **command - display cmd type
  • which cmd - display executable location
  • **help **cmd

** rm -r **- remove directory and its content

**info/man coreutils - **dispaly info (manual) about cmd

Installing something:

  • sudo apt install program

Redirection

  • **cat - **
  • **sort - **
  • **uniq - **
  • **grep - **
  • **wc - **
  • **head - **
  • **tail - **
  • tee -
  • **ls -l /usr/bin > ls-output.txt - **send output results to a file
  • **ls -l /usr/bin >> ls-output.txt - **append redirection to the same file (no owerwrite)
  • **ls -l /bin/usr 2> ls-error.txt - **redirect error to a file
  • **ls -l /bin/usr &> ls-output.txt **redirect output and error to the same file
    • 0 - input
    • 1 - output
    • 2 - error
  • /dev/null - location to discard putput etc.
    • ls -l /bin/usr 2> /dev/nullls

**Pipelines **used to filter commands

  • ls -l /usr/bin | less
  • **ls -l /bin /usr/bin | sort | less - **output of two directories sorted in one list
  • ls /bin /usr/bin | sort | uniq | less - removes any dublicates
  • **ls /bin /user/bin |sort | uniq -d | less - ** show list of dublicates

wc: - Print word, line, byte counts

grep: Print lines matching pattern

  • **grep **pattern filename
  • ls /bin /usr/bin | sort | uniq | grep zip_ - _programs that have zip in the name

head/tail - print first/last 10 lines

tail -f - usefull for watching the progress of log files