Thursday, May 6, 2021

How to setup PasswordLess SSH in Linux?

This tutorial answers your question i.e. How to setup Passwordless SSH?

SSH is a protocol to communicate a server with the client in an encrypted manner. It has replaced telnet protocol, which was not at all secure at all. Almost all the Linux system admins know about it because they use it to connect to Linux servers as the physical access to the server is very limited.

SSH is installed by default on most Linux distribution. & to access a server through ssh is very easy, you use the following command

$ ssh {Server IP address or FQDN}

and then you enter the credentials. But in this tutorial, we will learn to access ssh session securely with the help of Public/Private keys authentication aka passwordless ssh setup. Advantages of using Public/Private keys authentication are

You won’t be asked for a password every time you access the server (unless you are using a passphrase to decrypt the keys)
No-one can gain unauthorized access to your server unless they have the right key.

Now let’s create Public/Private keys for passwordless ssh setup to access our servers.

Setup PasswordLess SSH

Creating keys on the Local machine

Remember this, keys are to be created on each host that you wish to gain access from. So if there are 10-20 hosts from where you want to access a server, we must create keys on all those 10-20 servers.

To create keys, run the following command

$ ssh-keygen –t rsa

It will then ask you to select a location for the generated keys. By default, the keys will be stored in the ~/.ssh which is a hidden directory in your home folder (/home/dan/.ssh). The private key will be called id_rsa and the associated public key will be called id_rsa.pub.

It will also ask you to enter a passphrase, which is used to decrypt the keys. If you don’t wish to use any pass-phrase just leave it empty & press enter or else provide a pass-phrase.

Next, set permissions on your private keys,

$ chmod 700 ~/.ssh
$ chmod 600 ~/.ssh/id_rsa

Configuration on Remote Server

Now copy the Public key (id_rsa.pub) & move it to the remote server at /home/user/.ssh/authorized_keys folder. Now that the public keys have imported to server, remove them from local machine.

Next, we will also have to set permissions on the server as well

$ chmod 700 ~/.ssh
$ chmod 600 ~/.ssh/authorized_keys

All the settings for Public/Private keys authentication are now complete.

Testing the Public/Private keys authentication

Now log back into the local machine to access the server & enter

$ ssh {Server IP address or FQDN}

& hit enter. You will notice that you won’t be asked for the credentials & are logged directly into the server.

Once you have tested your passwordless ssh setup, you can also disable the use of password authentication so that everyone uses only keys to access the server. Thus making your servers more secure. To disable password authentication , open /etc/sshd/sshd_config & change the following parameter

PasswordAuthentication no

That’s it, this completes our tutorial on how to setup PasswordLess SSH on Linux machines.

Simple guide to install SSH on Ubuntu

SSH is one of the most widely used methods to access Linux & Unix servers. SSH provides an encrypted method to access & communicate between servers over insecure networks. In technical term, it’s a cryptographic protocol that allows for secured, encrypted communication between a host & a client.

In most of the Linux distributions, SSH comes installed & we can access those servers using ssh command but with Ubuntu Desktop (& based distros) that is not the case. We are required to install SSH on Ubuntu to be able access it.

Though we have an ssh client available on Ubuntu, it’s the ssh server that we need to install on Ubuntu. It means we can access other servers from Ubuntu using ssh but other machines will not be able to access our Ubuntu systems.

Install SSH on Ubuntu

SSH server is available with default Ubuntu repositories & we are not required to add any other repos to install it. We only need to run the following command to install it,

$ sudo apt update && sudo apt install openssh-server

Once installed, the ssh server will start on it’s own, but it required we can start it using the following command,

$ sudo systemctl start ssh

Check status with,

$ sudo systemctl status ssh

Note: If you have your firewall enabled on your Ubuntu system, then you would also be required to enable the ssh connections through the firewall. Run the following command to do so,

$ sudo ufw allow ssh

We can now access our Ubuntu system from other servers. Just open a ssh client & run the ssh command to access it,

$ ssh user@IP_ADDRESS

LINUX AIO - How To Configure X11 Forwarding Using SSH In Linux

How To Configure X11 Forwarding Using SSH In Linux

Today, we are going to learn a lesser known, interesting and useful feature about Linux. I am sure most of you know about SSH. We can access remote Linux systems securely via SSH. But, did you know that it is possible to forward X over SSH to run graphical applications remotely? Yes! This mechanism is known as X11 forwarding. In this guide, we are going to configure X11 forwarding using SSH in Linux.

What is X11 forwarding?

X11 forwarding is method of allowing a user to start a graphical applications installed on a remote Linux system and forward that application windows (screen) to the local system. The remote system need not to have X server or graphical desktop environment. Hence configuring X11 forwarding using SSH enables the users to securely run graphical applications over SSH session.

To put this in layman terms,

We connect to a remote system via SSH,
And then we launch a GUI application (which is installed in the remote system) from that SSH session,
Now, the GUI application runs on the remote system, but the application window appears on our local system. So we can use this remote GUI program on your local system as the way we use a locally installed program.

Clear? Now let us go ahead and see how to run remote GUI applications over SSH session.

Configure X11 Forwarding Using SSH In Linux

For the purpose of this guide, I will be using the following two systems:

Remote server - CentOS 8 minimal server (No GUI).
Local system - Ubuntu 20.04 LTS with Gnome DE.

Configuring X11 forwarding is trivial.

Make sure you have installed "xauth" on your remote serer system. If it is not installed, run the following command as root or sudo user:

# dnf install xorg-x11-xauth

Go to your remote system (in my case it is CentOS 8) and edit "/etc/ssh/sshd_config" file using your favorite editor:

# vi /etc/ssh/sshd_config

Add/modify following line:

[...]
X11Forwarding yes

Configure X11 Forwarding Using SSH In Linux

Press ESC key and type :wq to save and close the file.

Restart sshd service to effect the changes:

# systemctl restart sshd

Done! We have configured X11 forwarding.

Now go to your client system (in my case, it is Ubuntu 20.04) and access the remote server via SSH using command:

$ ssh -X root@192.168.225.52

Here, -X option is used to enable X11 forwarding over SSH. Replace "root@192.168.225.52" with your remote server's username and IP address.

You will see the following warning message at first time.

/usr/bin/xauth: file /root/.Xauthority does not exist

However, the .Xauthority file should be automatically generated during the first login, thus subsequent logins should be fine.

Next, launch any GUI applications from this SSH session. I already have installed Gedit graphical text editor in my CentOS 8 server, so I am going to launch it using command:

# gedit

The gedit GUI window screen will now appear in your local system.

Run remote graphical applications over SSH session in Linux

You can interact with the Gedit application installed on the remote server using your local system's display, mouse, and keyboard.

Even though my CentOS 8 server doesn't have GUI desktop, I can be able to open Gedit graphical editor and use it from my local Ubuntu system.

Configure X11 forwarding in Putty

If you use Putty client to access remote systems, enter your remote system's IP or hostname in the Session tab:

Connect to remote system using Putty

Next, navigate to Connection -> SSH -> X11 and enable X11 forwarding option. Click Open to establish a new Putty session:

Configure X11 forwarding in Putty

Enter the username and password of the remote server. Once you connected to the remote system via Putty, launch any X application installed in the remote server.

Run graphical applications over Putty session

Start interacting with the remote GUI application from your local system!

Saturday, February 13, 2021

How To Install Anaconda On Linux

This tutorial explains what is Anaconda Python distribution, the features of Anaconda, and how to install Anaconda on Linux operating system.

What is Anaconda distribution?

Anaconda is a cross-platform distribution of the Python and R programming languages. It is used for data science, machine learning, large-scale data processing and predictive analytics etc. Anaconda is available as four editions namely individual (open source) edition, commercial edition, team edition and enterprise edition. Anaconda individual edition is the world’s most popular Python distribution platform with over 20 million users worldwide. The Individual edition is free for personal use while the three other editions are commercial versions.

Anaconda ships with a command line package and virtual environment manager called Conda, which is used to manage and deploy applications, environments and packages. Conda was created for Python packages, however it can be used for other languages as well.

Using Conda utility, we can,

Create new Conda environments,
Install packages into specified Conda environment,
List packages in a Conda environment,
Update conda packages,
Search for packages,
Clean unused packages,
Remove packages from environments,
And more.

It also includes Anaconda Navigator, a graphical alternative for those who are not comfortable with the command line interface.

Anaconda features

Anaconda distribution enables the data scientists to:

download a collection of over 1500+ Python and R data science packages,
manage libraries, packages and virtual environments,
develop and train machine learning and deep learning models,
analyze data,
and visualize results using various tools.

Install Anaconda On Linux

As stated already, Anaconda Python distribution comes as free and paid editions. The Individual edition is free for personal use and learning purposes. For the purpose of this guide, I will be using Anaconda Individual edition.

Before installing Anaconda distribution on your Linux machine, make sure you have installed all required prerequisites.

If you are using Arch Linux and its derivatives like Manjaro Linux, install the following prerequistes:

$ sudo pacman -Sy libxau libxi libxss libxtst libxcursor libxcomposite libxdamage libxfixes libxrandr libxrender mesa-libgl  alsa-lib libglvnd

On Debian, Ubuntu and other DEB-based systems:

$ sudo apt install libgl1-mesa-glx libegl1-mesa libxrandr2 libxrandr2 libxss1 libxcursor1 libxcomposite1 libasound2 libxi6 libxtst6

On Fedora, CentOS, RHEL, AlmaLinux:

$ sudo dnf install libXcomposite libXcursor libXi libXtst libXrandr alsa-lib mesa-libEGL libXdamage mesa-libGL libXScrnSaver

On SUSE/openSUSE:

$ sudo zypper install libXcomposite1 libXi6 libXext6 libXau6 libX11-6 libXrandr2 libXrender1 libXss1 libXtst6 libXdamage1 libXcursor1 libxcb1 libasound2  libX11-xcb1 Mesa-libGL1 Mesa-libEGL1

After installing the prerequisites, download the latest Anaconda installer for Linux from Anaconda official download page:

$ wget https://repo.anaconda.com/archive/Anaconda3-2020.11-Linux-x86_64.sh

Go to the location where you downloaded the Anaconda installer and check the integrity of the downloaded file with SHA-256:

$ sha256sum Anaconda3-2020.11-Linux-x86_64.sh

You will see an output like below:

cf2ff493f11eaad5d09ce2b4feaa5ea90db5174303d5b3fe030e16d29aeef7de  Anaconda3-2020.11-Linux-x86_64.sh

Compare the above hash value with the official Hashes for Anaconda. If the hash value of the locally downloaded installer file matches with the official hash, you're good to go.

Now, start Anaconda installation using command:

$ bash Anaconda3-2020.11-Linux-x86_64.sh

You should include the bash command regardless of the shell you're using.

Press ENTER to continue installation:

Welcome to Anaconda3 2020.11

In order to continue the installation process, please review the license
agreement.
Please, press ENTER to continue
>>>

You will now see the license agreement. Press ENTER key to scroll to the bottom of the license terms and type “Yes” and press to agree the license agreement and continue installation.

Please answer 'yes' or 'no':'
>>> yes

Next the installer will prompt where do you want to install Anaconda. You will be given three choices. Press ENTER to accept the default install location. Press CTRL+C to cancel the installation or mention an alternate installation directory.

I go with the default installation path, which is /home/sk/anaconda3 in my case.

[...]
Anaconda3 will now be installed into this location:
/home/sk/anaconda3

  - Press ENTER to confirm the location
  - Press CTRL-C to abort the installation
  - Or specify a different location below

[/home/sk/anaconda3] >>>

If you've chosen the default location, the installer will display “PREFIX=/home/<user>/anaconda<2 or 3>” and continue the installation. It may take a few minutes to complete.

Next you will be prompted to initialize Anaconda. It is recommended to initialize it, so just type Yes and press ENTER to continue.

[...]
Preparing transaction: done
Executing transaction: done
installation finished.
Do you wish the installer to initialize Anaconda3
by running conda init? [yes|no]
[no] >>> yes

After a few seconds, you will see “Thank you for installing Anaconda3!” message if the installation is successful.

[...]
==> For changes to take effect, close and re-open your current shell. <==
 If you'd prefer that conda's base environment not be activated on startup, 
    set the auto_activate_base parameter to false: 
 conda config --set auto_activate_base false
 Thank you for installing Anaconda3!
 ===========================================================================
 Working with Python and Jupyter notebooks is a breeze with PyCharm Pro,
 designed to be used with Anaconda. Download now and have the best data
 tools at your fingertips.
 PyCharm Pro for Anaconda is available at: https://www.anaconda.com/pycharm

For the installation to take effect, close and re-open your Terminal. Alternatively, run the following command:

$ source ~/.bashrc

You will now see the prefix (base) in front of your shell prompt. It means that the conda's base environment is activated.

(base) sk@ostechnix:~$

If you don't want the conda's base environment activated by default on system startup and wish to run conda from anywhere, run the following command:

$ conda config --set auto_activate_base false

$ source ~/.bashrc

Now you won't see the prefix (base) in your shell prompt.

Multi-user Anaconda installation on Linux

By default, Anaconda will be installed for the current user only. If you wish to install Anaconda for all system users, create a common group, for example condagroup:

$ sudo group add condagroup

Replace "condagroup" with your own.

Change the group ownership to "condagroup" on the entire directory where Anaconda is installed. In my case, Anaconda is installed in /home/sk/anaconda3 directory, so I ran the following command:

$ sudo chgrp -R condagroup /home/sk/anaconda3

Replace /home/sk/anaconda3 with the actual path to your installed Anaconda file.

Next, set read and write permission for the owner, root, and the condagroup only using command:

$ sudo chmod 770 -R /home/sk/anaconda3

Finally, add all users to the newly created "condagroup":

$ sudo adduser ostechnix condagroup

Here, ostechnix is the user name and condagroup is the group name.

From now on, the users added to the "condagroup" group can able to access Anaconda, install packages, and create environments etc.

We have successfully installed Anaconda on our Linux machine. Let us verify if the Anaconda is installed correctly or not.

Verify Anaconda installation

We can verify Anaconda installation from commandline and/or from Anaconda Navigator GUI.

To verify Anaconda installation from commandline, run the following command:

$ conda list

If Anaconda is properly installed and working, you will see list of installed packages and their versions as shown in the following output:

packages in environment at /home/sk/anaconda3:
 #
 Name                    Version                   Build  Channel
 _ipyw_jlab_nb_ext_conf    0.1.0                    py38_0  
 _libgcc_mutex             0.1                        main  
 alabaster                 0.7.12                     py_0  
 anaconda                  2020.11                  py38_0  
 anaconda-client           1.7.2                    py38_0  
 anaconda-navigator        1.10.0                   py38_0  
 anaconda-project          0.8.4                      py_0  
 argh                      0.26.2                   py38_0  
 argon2-cffi               20.1.0           py38h7b6447c_1  
 asn1crypto                1.4.0                      py_0  
 astroid                   2.4.2                    py38_0  
[...]

The another method to verify the Anaconda installation is by entering into the Python shell.

To enter into Python shell, run:

$ python

This command will launch the Python shell. If Anaconda is installed and working, it will display "Anaconda, Inc." message as shown in the below output.

Python 3.8.5 (default, Sep  4 2020, 07:30:14) 
 [GCC 7.3.0] :: Anaconda, Inc. on linux
 Type "help", "copyright", "credits" or "license" for more information.

To exit the Python shell and go back to your shell prompt, enter the following command:

quit()

We can also verify Anaconda installation by opening Anaconda Navigator GUI.

Launch Anaconda Navigator graphical interface

We can manage packages and environments from command line using Conda package manager. If you're a newbie and bit uncomfortable with commandline, just use Anaconda Navigator GUI.

To launch Anaconda Navigator graphical interface, run the following command from your Terminal:

$ anaconda-navigator

The default interface of Anaconda Navigator will look like below:

As you can see, the Anaconda navigator includes many popular IDEs by default. As of writing this guide, it has the following 10 IDEs:

Datalore,
IBM Watson Studio Cloud,
JupyterLab,
Jupyter Notebook,
Qt Console,
Spyder,
Glueviz,
Orange,
PyCharm Professional,
RStudio.

Among the 10 IDEs, the first 6 IDEs were installed by default. You can use any IDE of your choice to write, run and debug your code.

Well, Anaconda is working!

Activate and deactivate Conda environment

By default, a Conda environment named base is created and activated.

If it is not activated by any chance, you can activate the Conda base environment using command:

$ conda activate

To deactivate it, run:

$ conda deactivate

Activate and deactivate Conda environment

Update Anaconda

Let first check the currently installed Conda version using command:

$ conda info

Sample output:

  active environment : base active env location : /home/sk/anaconda3         shell level : 1    user config file : /home/sk/.condarc
 populated config files : /home/sk/.condarc
           conda version : 4.9.2
     conda-build version : 3.21.4
          python version : 3.8.5.final.0
        virtual packages : __glibc=2.31=0
                           __unix=0=0
                           __archspec=1=x86_64
        base environment : /home/sk/anaconda3  (writable)
            channel URLs : https://repo.anaconda.com/pkgs/main/linux-64
                           https://repo.anaconda.com/pkgs/main/noarch
                           https://repo.anaconda.com/pkgs/r/linux-64
                           https://repo.anaconda.com/pkgs/r/noarch
           package cache : /home/sk/anaconda3/pkgs
                           /home/sk/.conda/pkgs
        envs directories : /home/sk/anaconda3/envs
                           /home/sk/.conda/envs
                platform : linux-64
              user-agent : conda/4.9.2 requests/2.25.1 CPython/3.8.5 Linux/5.4.0-65-generic ubuntu/20.04.2 glibc/2.31
                 UID:GID : 1000:1000
              netrc file : None
            offline mode : False

As you see, the current Conda version is 4.9.2.

Let us run the following command to see if there is any latest Conda version available:

$ conda update -n base conda

If there are any updates available, you will be prompted to update them. Just type y to install the updates:

To update all packages to the latest version of Anaconda, run:

$ conda update anaconda

Run a simple Python program from Python shell

Launch Python shell using command:

$ python

You will now see the >>> sign. It means you're in Python shell.

Inside the Python shell, type your code. For example, I type the following code:

print("Welcome to OSTechNix")

When you hit ENTER, you will see "Welcome to OSTechNix" message.

Run a simple Python program from Python shell

To exit the Python shell and go back to your shell prompt, enter the following command:

quit()

All done. We have installed Anaconda on our Linux machine, verified the Anaconda installation from command line as well as from Anaconda GUI, and finally run a sample Python program from Python shell.

In our upcoming articles, we will learn more about Anaconda Navigator GUI, Python IDEs, and Conda command line interface.

If you don't use Anaconda anymore, you can remove it from your system as shown below.

Uninstall Anaconda

First, you need to Install "anaconda-clean" module which is used to completely uninstall Anaconda from your system.

$ conda install anaconda-clean

Next, run the following command to remove Anaconda:

$ anaconda-clean --yes

Here, the --yes flag is used to delete all config files and directories.

The above command will create a backup directory called .anaconda_backup in your $HOME directory.

Backup directory: /home/sk/.anaconda_backup/2021-02-24T183205

And then, delete the entire Anaconda directory and the backup directory using commands:

$ rm -fr ~/anaconda3/

$ rm -fr ~/.anaconda_backup/

Finally, delete all Anaconda entries from your ~/.bashrc file.

Make the backup of ~/.bashrc file, just in case:

$ cp ~/.bashrc ~/.bashrc.bak

Open ~/.bashrc file using your preferred editor:

$ nano ~/.bashrc

Find the following lines and delete them. Please double check the lines before deleting them.

>>> conda initialize >>>
 !! Contents within this block are managed by 'conda init' !!
 __conda_setup="$('/home/sk/anaconda3/bin/conda' 'shell.bash' 'hook' 2> /dev/null)"
 if [ $? -eq 0 ]; then
     eval "$__conda_setup"
 else
     if [ -f "/home/sk/anaconda3/etc/profile.d/conda.sh" ]; then
         . "/home/sk/anaconda3/etc/profile.d/conda.sh"
     else
         export PATH="/home/sk/anaconda3/bin:$PATH"
     fi
 fi
 unset __conda_setup
 <<< conda initialize <<<

Delete Anaconda entries from bashrc file

Finally, run the following command to take effect the changes immediately:

$ source ~/.bashrc

That's it. Anaconda has been removed from your system.

Resource:

Anaconda website