Linux Basics¶

Linux is the basis of a lot of different operating systems. Many companies and developers release their own versions of linux called distributions or distros. The biggest companies being RedHat (RedHat Enterprise Linux) and Canonical (Ubuntu).

Linux basics cheat sheet¶

Basic commands¶

Some symbols have special meanings in the terminal:

/ refers to the root directory
. refers to your current working directory
~ refers to the current users home directory

Command	What it does
Navigate the filesystem
ls	Lists the files in your current working directory
cd <path or directory>	Move through the file system using either relative or absolute paths. `cd ..` to go up one directory
pwd	Prints your current working directory
File manipulation
cp <src> <dest>	Copies files or directories
mv <src> <dest>	Moves files or directories
rm [-r] <file or directory>	Deletes files (add -r to delete recursively)
cat <filename>	Print out the contents of a file
less <filename>	Prints out the contents of a file but with the ability to scroll and search by typing /. Quit with q
nano <filename>	Is a basic and easy to use text editor
mkdir <directoryname>	Creates a new directory
touch <filename>	Creates a new empty file
Miscellaneous
sudo <command>	Gives the user admin privileges for the command
man <command>	Opens a manual for the given command
history	Prints previously entered commands

Managing packages¶

Different distros use different tools to manage packages called package managers.\n I will use nano as an example package:\n Nano is a popular and very easy to use terminal text editor.\n Other examples would be Vim or Emacs but those aren’t as beginner friendly\n Debian and distros based on it use apt:

sudo apt update && sudo apt upgrade     # updates the system
apt search nano                         # search for nano in repositories
sudo apt install nano                   # installs nano
sudo apt remove nano                    # to remove the package

RedHat based distros like Almalinux use dnf:

sudo dnf update         # updates the system
dnf search nano         # search for nano in the repositories
sudo dnf install nano   # installs nano
sudo dnf remove nano    # to remove the package

Users¶

Creating a new user¶

The command used to create a new user is called useradd.

Just by running useradd your_user a new user named your_user will be created, but you probably want to add some parameters. The options of the useradd command are:

-m This will create a home directory in /home/your_user
-G group_name will add the newly created user to the here specified groups (wheel is an often used group since it allows the user to use sudo)
-s path/to/shell changes the default shell of the user. The available shells and their paths can be checked with cat /etc/shells. If the shell you want to use is not available it can be installed using the OSs package manager.

Modifying an existing user¶

In case you forgot to set something when creating the user, you can do that afterwards using the usermod command.

-aG to add another group to a user
-s to change the users default shell

For any additional options you might want to know you can always check the man pages using man usermod or any other command.

How to add an SSH key to a user?¶

This guide shows how to add an SSH key to an existing user with a home directory. The SSH daemon queries the .ssh/authorized_keys file and checks the content of this file against the provided private key.

If you are the responsible person of a project, and you don’t have access to an EODC VM please send your public key to support@eodc.eu and we will add the key for you.

You have to use the file with the .pub extension. The other key without a file extension is your private key and should never be shared with anybody. The private key is easily recognized by its beginning: -----BEGIN OPENSSH PRIVATE KEY-----

[remote_user@eodc ~]$ echo "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAACAQCmqcvQgmx6mPuhOsp...oC0oy1oiCRTcCNU4TWKwdpWEzxw== your_email@example.com" >> ~/.ssh/authorized_keys  
[remote_user@eodc ~]$ cat .ssh/authorized_keys    
    ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAACAQCmqcvQgmx6mPuhOsp...oC0oy1oiCRTcCNU4TWKwdpWEzxw== your_email@example.com
[remote_user@eodc ~]$ chmod 0600 ~/.ssh/authorized_keys

Groups¶

You can check the manual of the groupadd command in the terminal with man groupadd.

This article goes hand in hand with the User Creation Article.

Typically, a dedicated group is required for read and write access to your private EO-Storage. We will provide you a group ID in our welcome e-mail. After creating a VM, you will need to create the group separtely on each VM. Afterwards all users that shall have access to your private EO-Storage must be added to the group.

Create a group¶

To create a group, use the groupadd command: groupadd -g GROUP_ID group_name

Example using group ID 5000: groupadd -g 5000 group_name

Add a user to the group¶

Often used flags are -a (append) and -G (group). This tells usermod we are appending to the group name that follows the option.

ubuntu@eodc:~$ sudo usermod -aG sudo your_user
ubuntu@eodc:~$ sudo usermod -aG group2,group3,group4 your_user

You can check the user groups with the id command

ubuntu@eodc:~$ id your_user