Linux Beginner Guide¶

Basic Commands¶

- ps aux
$ ps - snapshot of of the current processes.

a = show processes for all users
u = display the process's user/owner
x = also show processes not attached to a terminal

- ip addr

$ ip addr | grep inet

- sudo
This SuperUserDo is the most important command Linux newbies will use. Every single command that needs root's permission, need this sudo command. You can use sudo before each command that requires root permissions -

$ sudo su

- ls (list)
The terminal will show you all the files and folders of the directory that you're working in. Let's say I'm in the /home folder and I want to see the directories & files in /home.

/home$ ls

- cd
​Changing directory (cd) is the main command that always be in use in terminal. It's one of the most Linux basic commands. Using this is easy. Just type the name of the folder you want to go in from your current directory. If you want to go up just do it by giving double dots (..) as the parameter.
​
/home $ cd usr

/home/usr $

- mkdir
Sometimes you want to create a new folder or subfolder. You can use mkdir command to do that. Just give your folder name after mkdir command in your terminal.

~$ mkdir folderName

- cp
copy-and-paste

$ cp source destination
Note: If you're copying files into the directory that requires root permission for any new file, then you'll need to use sudo command.

- rm
rm is a command to remove your file or even your directory. You can use -f if the file need root permission to be removed. And also you can use -r to do recursive removal to remove your folder.
$ rm myfile.txt

- apt-get in Ubuntu | pacman in Arch
This command differs distro-by-distro. In Debian based Linux distributions, to install, remove and upgrade any package we've Advanced Packaging Tool (APT) package manager.

​In other distributions, such as Arch, Centos there are different package managers.

$ sudo apt-get update | apt-get upgrade -y

$ sudo pacman -Syu

- grep
You need to find a file but you don't remember its exact location or the path. grep will help you to solve this problem. You can use the grep command to help finding the file based on given keywords.

$ grep user /etc/passwd

- cat
As a user, you often need to view some of text or code from your script. Again, one of the Linux basic commands is cat command. It will show you the text inside your file.

$ cat CMakeLists.txt

- poweroff
And the last one is poweroff. Sometimes you need to poweroff directly from your terminal. This command will do the task. Don't forget to add sudo at the beginning of the command since it needs root permission to execute poweroff.
$ sudo poweroff

Basic Linux Directories

• / – The Root Directory
  Everything on your Linux system is located under the / directory, known as the root directory.
  You can think of the / directory as being similar to the C:\ directory on Windows – but this isn’t strictly true, as Linux doesn’t have drive letters.
  While another partition would be located at D:\ on Windows, this other partition would appear in another folder under / on Linux.

• /bin – Essential User Binaries
  The /bin directory contains the essential user binaries (programs) that must be present when the system is mounted in single-user mode.
  Applications such as Firefox are stored in /usr/bin, while important system programs and utilities such as the bash shell are located in /bin.
  The /usr directory may be stored on another partition – placing these files in the /bin directory ensures the system will have these important
  utilities even if no other file systems are mounted. The /sbin directory is similar – it contains essential system administration binaries.

• /boot – Static Boot Files
  The /boot directory contains the files needed to boot the system – for example, the GRUB boot loader’s files and your Linux kernels are stored here.
  The boot loader’s configuration files aren’t located here, though – they’re in /etc with the other configuration files.

• /cdrom – Historical Mount Point for CD-ROMs
  The /cdrom directory isn’t part of the FHS standard, but you’ll still find it on Ubuntu and other operating systems.
  It’s a temporary location for CD-ROMs inserted in the system. However, the standard location for temporary media is inside the /media directory.

• /dev – Device Files
  Linux exposes devices as files, and the /dev directory contains a number of special files that represent devices.
  These are not actual files as we know them, but they appear as files – for example, /dev/sda represents the first SATA drive in the system.
  If you wanted to partition it, you could start a partition editor and tell it to edit /dev/sda.

This directory also contains pseudo-devices, which are virtual devices that don’t actually correspond to hardware.
For example, /dev/random produces random numbers. /dev/null is a special device that produces no output and automatically discards all input –
when you pipe the output of a command to /dev/null, you discard it.

• /etc – Configuration Files
  The /etc directory contains configuration files, which can generally be edited by hand in a text editor.
  Note that the /etc/ directory contains system-wide configuration files – user-specific configuration files are located in each user’s home directory.

• /home – Home Folders
  The /home directory contains a home folder for each user.
  For example, if your user name is bob, you have a home folder located at /home/bob. This home folder contains the user’s data files and user-specific configuration files.
  Each user only has write access to their own home folder and must obtain elevated permissions (become the root user) to modify other files on the system.

• /lib – Essential Shared Libraries
  The /lib directory contains libraries needed by the essential binaries in the /bin and /sbin folder.
  Libraries needed by the binaries in the /usr/bin folder are located in /usr/lib.

• /lost+found – Recovered Files
  Each Linux file system has a lost+found directory. If the file system crashes, a file system check will be performed at next boot.
  Any corrupted files found will be placed in the lost+found directory, so you can attempt to recover as much data as possible.

• /media – Removable Media
  The /media directory contains subdirectories where removable media devices inserted into the computer are mounted.
  For example, when you insert a CD into your Linux system, a directory will automatically be created inside the /media directory.
  You can access the contents of the CD inside this directory.

• /mnt – Temporary Mount Points
  Historically speaking, the /mnt directory is where system administrators mounted temporary file systems while using them.
  For example, if you’re mounting a Windows partition to perform some file recovery operations, you might mount it at /mnt/windows.
  However, you can mount other file systems anywhere on the system.

• /opt – Optional Packages
  The /opt directory contains subdirectories for optional software packages.
  It’s commonly used by proprietary software that doesn’t obey the standard file system hierarchy –
  for example, a proprietary program might dump its files in /opt/application when you install it.

• /proc – Kernel & Process Files
  The /proc directory similar to the /dev directory because it doesn’t contain standard files. It contains special files that represent system and process information.

• /root – Root Home Directory
  The /root directory is the home directory of the root user. Instead of being located at /home/root, it’s located at /root.
  This is distinct from /, which is the system root directory.

• /run – Application State Files
  The /run directory is fairly new, and gives applications a standard place to store transient files they require like sockets and process IDs.
  These files can’t be stored in /tmp because files in /tmp may be deleted.

• /sbin – System Administration Binaries
  The /sbin directory is similar to the /bin directory. It contains essential binaries that are generally intended to be run by the root user for system administration.

• /selinux – SELinux Virtual File System
  If your Linux distribution uses SELinux for security (Fedora and Red Hat, for example), the /selinux directory contains special files used by SELinux.
  It’s similar to /proc. Ubuntu doesn’t use SELinux, so the presence of this folder on Ubuntu appears to be a bug.

• /srv – Service Data
  The /srv directory contains “data for services provided by the system.”
  If you were using the Apache HTTP server to serve a website, you’d likely store your website’s files in a directory inside the /srv directory.

• /tmp – Temporary Files
  Applications store temporary files in the /tmp directory.
  These files are generally deleted whenever your system is restarted and may be deleted at any time by utilities such as tmpwatch.

• /usr – User Binaries & Read-Only Data
  The /usr directory contains applications and files used by users, as opposed to applications and files used by the system.
  For example, non-essential applications are located inside the /usr/bin directory instead of the /bin directory and non-essential system administration binaries are
  located in the /usr/sbin directory instead of the /sbin directory. Libraries for each are located inside the /usr/lib directory.
  The /usr directory also contains other directories – for example, architecture-independent files like graphics are located in /usr/share.

The /usr/local directory is where locally compiled applications install to by default – this prevents them from mucking up the rest of the system.

• /var – Variable Data Files
  The /var directory is the writable counterpart to the /usr directory, which must be read-only in normal operation.
  Log files and everything else that would normally be written to /usr during normal operation are written to the /var directory.
  For example, you’ll find log files in /var/log.

beginner tutorials
h3. Ping
1. ping hostname or domain¶

$ ping google.ch

PING google.ch(zrh11s02-in-x03.1e100.net (2a00:1450:400a:800::2003)) 56 data bytes
64 bytes from zrh11s02-in-x03.1e100.net (2a00:1450:400a:800::2003): icmp_seq=1 ttl=57 time=4.02 ms

2. ping via IPv4

$ ping 10.3.10.37

PING 10.3.10.37 (10.3.10.37) 56(84) bytes of data.
64 bytes from 10.3.10.37: icmp_seq=1 ttl=64 time=0.037 ms

3. ping via IPv6

$ ping 2a00:1450:400a:800::2003

PING 2a00:1450:400a:800::2003(2a00:1450:400a:800::2003) 56 data bytes
64 bytes from 2a00:1450:400a:800::2003: icmp_seq=1 ttl=57 time=5.00 ms