Linux

Linux

Linux is a family of operating systems famous for its kernel.
Linux comes with a lot of free office, system monitoring and programming tools, such as OpenOffice and process control program top.

Linux distributions

There are many varieties of Linux. They range from those that look like Microsoft Windows to those without a GUI.
Each Linux OS is different, so take care not to mix up installation instructions or command syntax.

• Manjaro - popular
• Ubuntu - Desktop is like Windows, Server has no GUI
• CentOS - for servers
• Alpine - tiny OS for container images, routers, firewalls, VPNs and servers

Installation

Linux distributions can be installed using a USB, a DVD or a virtualisation software such as VirtualBox.

Paths and directories

Absolute path: prefixed with /  
Relative path: without prefix /  

Current directory: .
Parent directory: ..
Hidden directory: prefixed with .

Common Hotkeys

Paste: SHIFT+INSERT
Search: SHIFT+W

Autocomplete: TAB; double TAB

Switch workspace: CTRL+ALT+UP/DOWN

Common Commands

$: man Command-Name  # show manual; "q" to exit
$: info Command-Name  # show command info

$: ls [-l] [-d] [-R]  # list directory contents
  # -l: show permissions, owner, ...
  # -d: describe current directory
  # -R: recursive
$: pwd  # show current directory path
$: cd /path/to  # change directory

$: apt/apt-get: Ubuntu package manager
$: yum: CentOS package manager
$: apk: Alpine package manager
$: tar -xzvf Package-Name  # extract/untar

$: bash Script-Name  # run script
$: sh Script-Name  # run script

$: sudo Command-Name  # run as admin/superuser
$: chmod Access-Modifiers File-Name  # modify access restrictions
$: sudo su - # login as root/superuser


$: touch File-Name  # create a file
$: cat File-Name  # show file
$: mv /path/to/Old-Dir-Name /path/to/New-Dir-Name  # move or rename file
$: cp /path/to/Dir-Name /path/to/New-Dir-Name [-r]  # copy directory
  # -r: recursive
$: rm /path/to/Dir-Name [-r] [-f]  # remove directory
  # -r: recursive
  # -f: force delete
$: rmdir /path/to/Dir-Name  # remove directory if empty

$: nano File-Name  # text editor
$: vim File-Name  # text editor


$: env  # print all ENV VAR
$: printenv  # print all ENV VAR
$: echo Value-Literal  # print value
$: echo $Value-Name  # list ENV VAR value
$: export Value-Name=_value  # set ENV VAR value

$: ps  # list Process IDs (PID)
$: kill PID  # SIGTERM/soft shutdown
$: kill -9 PID  # SIGKILL/hard shutdown

$: find / -name 'Search-Name'

$: lsb_release -a  # OS info
$: uname -m  # list architecture
  # armv5* == armv5
  # armv6* == armv6
  # armv7* == arm
  # aarch64 == arm64
  # x86 == 386
  # x86_64 == amd64
  # i686 == 386
  # i386 == 386

|: pipe output
>: overwrite a file
>>: append to file

$: ... | grep "Search-Term"  # filter

$: ... | grep -i "search-term"  # case insensitive

$: ... | grep -v "Search-Term"  # NOT
$: ... | grep "term1\|term2"  # OR
$: ... | grep -E "term1|term2"  # OR

&  # detach process

Network commands

$: netcat -l -p PORT  # create listener server
$: nc ...

$: ifconfig  # network interfaces
$: netstat  # network statistics
$: netstat -plunt  # discover which service exposes which port
$: ip addr  #
$: ip link  #
$: ip route  #
$: ss  #
$: ip -s  #

Remote files

$: scp [-i Private-Key][-P Port] /source/path/File-Name User-Name@_ip:/destination/path
  # @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
  # @         WARNING: UNPROTECTED PRIVATE KEY FILE!          @
  # @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
  # ...
  # Note: use $: sudo chmod 600 Private-Key

$: sftp -oPort=Post-Number User-Name@Host-Name  # manipulate files on a remotely

Setting PATH and DNS

Place an executable in /usr/local/bin and you'll be able to run it.

Set ENV VAR in sudo nano ~/.bashrc.

Set PATH in:

• /etc/environment
• .bashrc which is in root

Set DNS in:

• /etc/hosts

Generating an SSH key pair

Windows

See PuTTY.

$: git-gui
# Note: Help -> Show SSH Key -> Generate Key -> Copy (Public Key) To Clipboard

Linux

$: ssh-keygen -t ed25519 -C "SSH-Key-Name"   # generates a public-private key pair
  # Enter file in which to save the key (/home/_user/.ssh/id_ed25519): /home/_user/.ssh/id_ed25519-Name
$: cat /home/_user/.ssh/id_ed25519-Name.pub   # prints the PUBLIC key
  # ssh-ed25519 A-Long-String SSH-Key-Name