8 Common Uses of the Linux Touch Command

https://vitux.com/8-common-uses-of-the-linux-touch-command

The Linux touch command can be used for much more than simply creating an empty file on Linux. You can use it to change the timestamp of existing files including their access as well as modification times. This article presents 8 scenarios where you can utilize the touch command through your Linux Terminal.
We have run the commands and procedures mentioned in this article on a Ubuntu 18.04 LTS system. Since the touch command is a command line utility, we will be using the Ubuntu Terminal for this article. You can open the Terminal either through the system Dash or the Ctrl+Alt+T shortcut.

1. Create a single empty file with the touch command

The simplest and the most basic use of the touch command is to create an empty file through the command line. If you are a Terminal-savvy person, you can quickly create a new file in the command line through the following command:
$ touch “filename”
Example:

$ touch samplefile

In the following example, I have created an empty file with the name “samplefile” through the touch command. I have then used the ls command to view the presence of the file on my system as the touch command does not prompt if the file has been created or not.

2. Create multiple files at once with touch command

Although the cat command and the standard redirect symbol are also ways to create files through the command line, the touch command takes an edge because you can create multiple files with it at once. You can use the following syntax in order to create multiple files through the touch command:

$ touch samplefile1 samplefile2 samplefile3 ….

In the following example I have created three files simultaneously through the touch command and then used the ls command in order to view the presence of those files:

3. Force avoid creating a new file with touch command

At times there is a need to avoid creating a new file if it already does not exist. In that case, you can use the ‘-c’ option with the touch command as follows:

$ touch -c “filename”

In the following example, I have used the touch command to forcefully avoid the creation of the mentioned new file.

When I use the ls command to list that file, the following output verifies that such a file does not exist in my system.

4. Change both access and modification times of a file

Another use of the touch command is to change both the access time and the modification time of a file.
Let us present an example to show how you can do it. I created a file named “testfile” through the touch command and viewed its statistics through the stat command:

Then I entered the following touch command:

$ touch testfile

This touch command changed the access and modification time to the time when I ran the touch command again for the “testfile”. You can see the changed access and modification times in the following image:

5. Change either access time or modification time

Instead of changing both the access and modification times, we can choose to change only one of them through the touch command.
In the following example, I created a file by the name of “samplefile” and viewed it statistics through the stat command:

I can change only the access time of this file by using the ‘-a’ option through the touch command on this file:

$ touch -a samplefile

The output of the stat command now shows that the access time has been changed to the time when I ran the touch command with the ‘-a’ option:

I can change only the modification time of this file by using the ‘-m’ option through the touch command on this file:

$ touch -m samplefile

The output of the stat command now shows that the modification time has been changed to the time when I ran the touch command with the ‘-m’ option:

6. How to copy access & modification time from one file to another file

Let us suppose we have a file named samplefileA:

And another file named samplefileB:

If you want to change the access & modification time of samplefileA to that of the samplefileB, you can sue the touch command as follows:

$ touch samplefileA -r sampleFileB

The output of the stat command in the above image shows that the samplefileA now has the same access and modify values as that of samplefileB.

7. Create a new file with a specified timestamp

In order to create a new empty file with a specified timestamp instead of the actual time you created it, you can use the following syntax of the touch command:

$ touch -t YYMMDDHHMM.SS “filename”

The following example shows how the stat command on my samplefile shows that its access and modification times are based on the timestamp I provided while creating it through the touch command:

8. Change timestamp of a file to some other time

You can change the timestamp of an existing file to some other time using the following syntax of the touch command:

$ touch -c -t YYMMDDHHMM.SS “filename”

In the following example, I have changed the timestamp of an existing file through the touch command and then verified the changes through the stat command on that sample file:

Through the basic yet useful scenarios we presented in this article, you can begin to master the touch command and use it for quickly performing some seemingly complex tasks through the Linux command line.

How to Multi-Task in Linux with the Command Line

https://www.rosehosting.com/blog/how-to-multi-task-in-linux-with-the-command-line

How to Multi-Task in Linux with the Command Line

One of the most jarring moments when moving from a Windows-based environment to using the command line is the loss of easy multi-tasking. Even on Linux, if you use an X Window system, you can use the mouse to just click on a new program and open it. On the command line, however, you’re pretty much stuck with what’s on your screen at any given time. In this tutorial, we will show you how to multi-task in Linux with the command line.

Background and Foreground Process Management

However, there are still ways to multi-task in Linux, and some of them are more comprehensive than others. One in-built way that doesn’t require any kind of additional software is simply moving processes into the background and the foreground. We’d written a tutorial on that a short while back. However, it has some disadvantages.

Disadvantages

First, to send a process into the background, you have to pause it first. There’s no way to send an already running program into the background and keep it running in one go.
Second, you need to break your workflow to start a new command. You have to exit what you’re currently doing and type more commands into the shell. It works, but it’s inconvenient.
Third, you have to look out for output from the background processes. Any output from them will appear on the command line and interfere with what you’re doing in the current moment. So background tasks need to either redirect their output to a separate file, or they need to be muted altogether.
Because of these disadvantages, there are huge problems with background and foreground process management. A better solution is to use the “screen” command utility as shown below.

But First – You Can Always Open a new SSH Session

Don’t forget that you just open a new SSH session. Here’s a screenshot of we doing just that:

It can get inconvenient to open new sessions all the time. And that’s when you need “screen”

Using “Screen” Instead

The “screen” utility allows you to have multiple workflows open at the same times – the closest analog to “windows”. It’s available by default within the regular Linux repositories. Install it in CentOS/RHEL like this:

sudo yum install screen

Opening a New Screen

Now start your session by typing “screen”.
This will create a blank window within your existing SSH session and give it a number that’s shown in the title bar like this:

My screen here has the number “0” as shown. In this screenshot, I’m using a dummy “read” command to block the terminal and make it wait for input. Now let’s say we want to do something else while we wait.
To open a new screen and do something else, we type:

ctrl+a c

“ctrl+a” is the default key combination for managing screens within the screen program. What you type after it, determines the action. So for example:

• ctrl+a c – Creates a new screen
• ctrl+a [number] – Goes to a specific screen number
• ctrl+a k – Kills the current screen
• ctrl+a n – Goes to the next screen
• ctrl+a ” – Lists all active screens in the session

So if we press “ctrl+a c”, we get a new screen with a new number as shown here:

You can use the cursor keys to navigate the list and go to whichever screen you want.
Screens are the closest thing you’ll get to a “windows” like system in the Linux command line. Sure, it’s not as easy as clicking with the mouse, but then the graphical subsystem is very resource intensive in the first place. With screens, you can get almost the same functionality and enable full multi-tasking!

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How to start a vnc server for the actual display (scraping) with TigerVNC

https://www.howtoforge.com/tutorial/how-to-start-a-vnc-server-for-the-actual-display-scraping-with-tigervnc

VNC is a desktop sharing application (Virtual Network Computing) to connect and control a (remote or local) computer's desktop over a network connection.
However, on linux systems, many VNC server applications allow only to connect to a virtual desktop and not to the actual one. This howto offers you a solution, to connect via TigerVNC server to the actual active session on your Linux desktop.

Requirements

• A fully functional linux desktop environment
• root privilege (to install the TigerVNC server)
• basic knowledge of the linux shell

In order to get the latest packages, you may want to update.

user@hostname:~$ sudo apt-get update

This howto was tested on Debian/GNU Linux 9.5 (stretch) and Ubuntu 18.04

Install TigerVNC

First, you have to install the TigerVNC server.

user@hostname:~$ sudo apt-get install tigervnc-scraping-server

Note, that on most debian-based systems, there is a small package called tigervnc-scraping-server, which you need to install. You don't have to install the main TigerVNC server (package name: tigervnc-standalone-server) to have the functionality to connect to the running desktop session, only if you prefer to connect to a virtual desktop, too.
The TigerVNC server provides a smaller application (x0vncserver) to grant access to the active session.
Then, create a .vnc directory in your home:

user@hostname:~$ mkdir -p ~/.vnc

Create a password for your vnc session:

user@hostname:~$ vncpasswd
Password:
Verify:
Would you like to enter a view-only password (y/n)? n

Starting the VNC server

A short description of the x0vncserver:

x0tigervncserver is a TigerVNC Server which makes any X display remotely accessible via VNC, TigerVNC or compatible viewers. Unlike Xvnc(1), it does not create a virtual display. Instead, it just shares an existing X server (typically, that one connected to the physical screen).

Now that you have successfully installed TigerVNC server on your computer, created a password with the vncpasswd command, we can begin to start our vnc server. Make sure that you're on the active session, and write (as user):

user@hostname:~$ x0vncserver -passwordfile ~/.vnc/passwd -display :0

Wed Oct 10 22:17:16 2018
Geometry: Desktop geometry is set to 1920x1080+0+0
Main: XTest extension present - version 2.2
Main: Listening on port 5900

The option -passwordfile ~/.vnc/passwd reads the password file created earlier with the vncpasswd command. The second option -display :0 means, that you want to connect to the session on the display :0, which is usually the active session.
Now you can access your actual desktop with any vnc viewer application on the default vnc port 5900.
You can stop this process whenever you want by pressing Ctrl-c.
If you wish to run it in the background, type:

user@hostname:~$ x0vncserver -passwordfile ~/.vnc/passwd -display :0 >/dev/null 2>&1 &

Now all the output standard output and errors are redirected to /dev/null and with the & at the end, it will run in the background. However, you won't be able anymore to stop the vnc server by pressing Ctrl-c, instead you have to kill it's process id (see below section "Stopping the vnc server").
For more options and syntax, check the x0vncserver manual.

Stopping the VNC server

If your vnc server runs in the background, you have to know the process id, in order to stop it.

user@hostname:~$ ps -fu user | grep [x]0vncserver
user    1328    1   0 23:11 pts/2    00:00:00    /usr/bin/x0vncserver -display :0 -passwordfile /home/user/.vnc/passwd -rfbport 5900

The output will be like this, so notice the pid 1328. In order to stop the vnc server, we have to "kill" this process.

user@hostname:~$ kill -9 1328

The option -9 for the kill command will send the KILL signal to the process id to make sure that it stops.

Script to run the VNC server

There is a script to start and stop the x0vncserver application on github. For testing purposes, you download the psmisc package, too:

user@hostname:~$ sudo apt-get install git psmisc

Then, download the startvnc script using the git command:

user@hostname:~$ git clone https://github.com/sebestyenistvan/runvncserver
Cloning into 'runvncserver'...
remote: Enumerating objects: 77, done.
remote: Counting objects: 100% (77/77), done.
remote: Compressing objects: 100% (57/57), done.
remote: Total 77 (delta 25), reused 60 (delta 18), pack-reused 0
Unpacking objects: 100% (77/77), done.

Your output will look something like above.
Copy the startvnc script from the runvncserver directory to your home:

user@hostname:~$ cp ~/runvncserver/startvnc ~

Change permissions to executable, in order to execute the script:

user@hostname:~$ chmod +x ~/startvnc

Then, run the script.

user@hostname:~$ ./startvnc

Usage: ./startvnc start|stop|restart|status

This script will only work, if you have a .vnc directory in your home and created a vncpasswd (it checks for ~/.vnc/passwd file). We already created the .vnc directory and the password earlier.

To start the vnc server on the actual display, just type:

user@hostname:~$ ./startvnc start
Starting VNC Server on display :0 [ok]

You can test, if your vnc server is running with the option:

user@hostname:~$ ./startvnc status
Status of the VNC server: [running] (pid: 1328)

Few examples:

Or by checking the 5900 TCP port on your system with the fuser command (from the psmisc package):

user@hostname:~$ fuser -vn tcp 5900
                  USER      PID     ACCESS      COMMAND
5900/tcp:         user      1328    F....       x0vncserver

You'll get an output like this if the vnc server is running on port 5900.

More instructions for this script you can find in the readme file:

user@hostname:~$ less runvncserver/README.md

The script will create a logfile, where the output is stored. If something goes wrong or you can't start or stop the x0vncserver, take a look at the logfile under ~/.vnc/logfile

Start the VNC server automatically

If you want to access the active desktop session automatically, you need to edit the .xsessionrc file in your home directory.

user@hostname:~$ echo "/home/user/startvnc start >/dev/null 2>&1" >> ~/.xsessionrc

 Replace user by your username and it will automatically run when starting the X session. The script logs its activity in ~/.vnc/logfile, if something goes wrong, you can check the log file there.

Notes

This tutorial doesn't deal with setting up a VNC virtual desktop.

Security

Be aware, that the x0vncserver doesn't use encryption by default, so use it carefully over the internet. If you want to use it remotely, you can tunnel it via ssh. However, there are other howtos where you can find a solution to encrypt your VNC session.
Or you can take a look at the ssvnc package.

VNC viewers

If you're looking for VNC viewers, there are plenty of them, for instance:

• gvncviewer
• tigervnc-viewer
• xtightvncviewer
• xvnc4viewer

Geometry

The x0vncserver on the actual display will use the same geometry as the running desktop on the :0 display. So if you set the -geometry option to a lower size, it won't get scaled, you'll just see a fraction of the desktop size.

Feedback

Feel free to write feedback. If you tested this tutorial or even the script on another system.

Linux tr Command Tutorial for Beginners (with Examples)

https://www.howtoforge.com/linux-tr-command

Depending on the kind of work you do on the command line in Linux, you may want a utility that can act as a Swiss army knife of quick text editing. Gladly, there exists a tool dubbed tr, which qualifies for this role. In this tutorial, we will discuss the basics of tr using some easy to understand examples.

But before we do that, it's worth mentioning that all examples in this article have been tested on an Ubuntu 18.04 LTS machine.

Linux tr command

Here's how the tool's man page explains it:

Translate, squeeze, and/or delete characters from standard input, writing to standard output.

And following is its syntax:

tr [OPTION]... SET1 [SET2]

here's what SET means:

SETs are specified as strings of characters.  Most represent themselves.  Interpreted sequences are:

       \NNN   character with octal value NNN (1 to 3 octal digits)

       \\     backslash

       \a     audible BEL

       \b     backspace

       \f     form feed

       \n     new line

       \r     return

       \t     horizontal tab

       \v     vertical tab

Following are some Q&A styled examples that should give you a better idea on how the tr command works.

Q1. How to convert lower case to upper case using tr?

Suppose you want to convert the sentence "linux tutorial on howtoforge" to uppercase, then here's how you can do this using tr.

echo 'linux tutorial on howtoforge' | tr "[:lower:]" "[:upper:]"

The above command produced the following output on my system:

LINUX TUTORIAL ON HOWTOFORGE

Q2. How to strip extra spaces using tr?

Suppose you have a line like: "HowtoForge       is an extremely        good resource for      Linux tutorials". And the requirement is to strip extra spaces from this line.
Here's how you can use tr to do this:

echo 'HowtoForge       is an extremely        good resource for      Linux tutorials' | tr -s '[:space:]'

Here's the output:

HowtoForge is an extremely good resource for Linux tutorials

Q3. How to delete text using tr?

Suppose you want to delete the hyphens from the following line: "HowtoForge -- is -- an -- extremely -- good -- resource -- for -- Linux -- tutorials." Then here's how you can do this using tr.

echo 'HowtoForge -- is -- an -- extremely -- good -- resource -- for -- Linux -- tutorials' | tr -d '-'

Following is the output it produces:

HowtoForge  is  an  extremely  good  resource  for  Linux  tutorials

Q4. How to replace characters using tr?

In the previous section, suppose the requirement was to replace hyphens with, let's say, dots. Then here's how you can do that using tr.

echo 'HowtoForge -- is -- an -- extremely -- good -- resource -- for -- Linux -- tutorials' | tr '-' '.'

Following is the output it produced:

HowtoForge .. is .. an .. extremely .. good .. resource .. for .. Linux .. tutorials

Conclusion

So you can see the tr command is an extremely helpful tool when it comes to editing text. We have discussed some main options here, but the utility offers many other command line options as well. First try these, and once you've got a good idea about what we've discussed here, then you can learn more about tr by heading to its man page.

How to compile and install Linux Kernel 4.19 from source code

https://www.cyberciti.biz/tips/compiling-linux-kernel-26.html

Compiling a custom kernel has its advantages and disadvantages. However, new Linux user/admin find it difficult to compile Linux kernel. Compiling kernel needs to understand few things and then type a couple of commands. This step by step howto covers compiling Linux kernel version 4.19.xx under an Ubuntu or Debian Linux. The following instructions successfully tested on an RHEL 7/CentOS 7 (and clones), Debian Linux, Ubuntu Linux and Fedora Linux 28. However, instructions remain the same for any other Linux distribution.

How to compile and install Linux Kernel 4.19

The procedure to build (compile) and install the latest Linux kernel from source is as follows:

1. Grab the latest kernel from kernel.org
2. Verify kernel
3. Untar the kernel tarball
4. Copy existing Linux kernel config file
5. Compile and build Linux kernel 4.19
6. Install Linux kernel and modules (drivers)
7. Update Grub configuration
8. Reboot the system

Let us see all steps in details.

Step 1. Get the latest Linux kernel source code

Visit the official project site and download the latest source code. Click on the big yellow button that read as “Latest Stable Kernel“:

The filename would be linux-x.y.z.tar.xz, where x.y.z is actual Linux kernel version number. For example file linux-4.19.tar.xz represents Linux kernel version 4.19. Use the wget command to download Linux kernel source code:
$ wget https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.19.tar.xz

Step 2. Extract tar.xz file

You really don’t have to extract the source code in /usr/src. You can extract the source code in your $HOME directory or any other directory using the following unzx command or xz command:
$ unzx -v linux-4.19.tar.xz
OR
$ xz -d -v linux-4.19.tar.xz

Verify Linux kernel tartball with pgp

First grab the PGP signature for linux-4.19.tar:
$ wget https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.19.tar.sign
Try to verify it:
$ gpg --verify linux-4.19.tar.sign
Sample outputs:

gpg: assuming signed data in 'linux-4.19.tar'
gpg: Signature made Sun 12 Aug 2018 04:00:28 PM CDT
gpg:                using RSA key 79BE3E4300411886
gpg: Can't check signature: No public key

Grab the public key from the PGP keyserver in order to verify the signature i.e. RSA key ID 79BE3E4300411886 (from the above outputs):
$ gpg --recv-keys 79BE3E4300411886
Sample outputs:

gpg: key 79BE3E4300411886: 7 duplicate signatures removed gpg: key 79BE3E4300411886: 172 signatures not checked due to missing keys gpg: /home/vivek/.gnupg/trustdb.gpg: trustdb created gpg: key 79BE3E4300411886: public key "Linus Torvalds " imported gpg: no ultimately trusted keys found gpg: Total number processed: 1 gpg: imported: 1

Now verify gpg key again with the gpg command:
$ gpg --verify linux-4.19.tar.sign
Sample outputs:

gpg: assuming signed data in 'linux-4.19.tar' gpg: Signature made Sun 12 Aug 2018 04:00:28 PM CDT gpg: using RSA key 79BE3E4300411886 gpg: Good signature from "Linus Torvalds " [unknown] gpg: aka "Linus Torvalds " [unknown] gpg: WARNING: This key is not certified with a trusted signature! gpg: There is no indication that the signature belongs to the owner. Primary key fingerprint: ABAF 11C6 5A29 70B1 30AB E3C4 79BE 3E43 0041 1886

If you do not get “BAD signature” output from the “gpg –verify” command, untar/extract the Linux kernel tarball using the tar command, enter:
$ tar xvf linux-4.19.tar

Step 3. Configure the Linux kernel features and modules

Before start building the kernel, one must configure Linux kernel features. You must also specify which kernel modules (drivers) needed for your system. The task can be overwhelming for a new user. I suggest that you copy existing config file using the cp command:
$ cd linux-4.19
$ cp -v /boot/config-$(uname -r) .config
Sample outputs:

'/boot/config-4.15.0-30-generic' -> '.config'

Step 4. Install the required compilers and other tools

You must have development tools such as GCC compilers and related tools installed to compile the Linux kernel.

How to install GCC and development tools on a Debian/Ubuntu Linux

Type the following apt command or apt-get command to install the same:
$ sudo apt-get install build-essential libncurses-dev bison flex libssl-dev libelf-dev
See “Ubuntu Linux Install GNU GCC Compiler and Development Environment” for more info.

How to install GCC and development tools on a CentOS/RHEL/Oracle/Scientific Linux

Try yum command:
$ sudo yum group install "Development Tools"
OR
$ sudo yum groupinstall "Development Tools"
Additional packages too:
$ sudo yum install ncurses-devel bison flex elfutils-libelf-devel openssl-devel

How to install GCC and development tools on a Fedora Linux

Run the following dnf command:
$ sudo dnf group install "Development Tools"
$ sudo dnf ncurses-devel bison flex elfutils-libelf-devel openssl-devel

Step 5. Configuring the kernel

Now you can start the kernel configuration by typing any one of the following command in source code directory:

• $ make menuconfig – Text based color menus, radiolists & dialogs. This option also useful on remote server if you wanna compile kernel remotely.
• $ make xconfig – X windows (Qt) based configuration tool, works best under KDE desktop
• $ make gconfig – X windows (Gtk) based configuration tool, works best under Gnome Dekstop.

For example, run make menuconfig command launches following screen:
$ make menuconfig

You have to select different options as per your need. Each configuration option has HELP button associated with it so select help button to get help. Please note that ‘make menuconfig’ is optional. I used it here to demonstration purpose only. You can enable or disable certain features or kernel driver with this option. It is easy to remove support for a device driver or option and end up with a broken kernel. For example, if the ext4 driver is removed from the kernel configuration file, a system may not boot. When in doubt, just leave support in the kernel.

Step 5. How to compile a Linux Kernel

Start compiling and tocreate a compressed kernel image, enter:
$ make
To speed up compile time, pass the -j as follows:
## use 4 core/thread ##
$ make -j 4
## get thread or cpu core count using nproc command ##
$ make -j $(nproc)

Compiling and building the Linux kernel going take a significant amount of time. The build time depends upon your system’s resources such as available CPU core and the current system load. So have some patience.

Install the Linux kernel modules

$ sudo make modules_install

Install the Linux kernel

So far we have compiled the Linux kernel and installed kernel modules. It is time to install the kernel itself:
$ sudo make install

It will install three files into /boot directory as well as modification to your kernel grub configuration file:

• initramfs-4.19.img
• System.map-4.19
• vmlinuz-4.19

Step 6. Update grub config

You need to modify Grub 2 boot loader configurations. Type the following command at a shell prompt as per your Linux distro:

CentOS/RHEL/Oracle/Scientific and Fedora Linux

$ sudo grub2-mkconfig -o /boot/grub2/grub.cfg
$ sudo grubby --set-default /boot/vmlinuz-4.19
You can confirm the details with the following commands:
grubby --info=ALL | more
grubby --default-index
grubby --default-kernel

Debian/Ubuntu Linux

The following commands are optional as make install does everything for your but included here for historical reasons only:
$ sudo update-initramfs -c -k 4.19
$ sudo update-grub

How to build and install the latest Linux kernel from source code

You have compiled a Linux kernel. The process takes some time, however now you have a custom Linux kernel for your system. Let us reboot the system.

Reboot Linux computer and boot into your new kernel

Just issue the reboot command or shutdown command:
# reboot
Verify new Linux kernel version after reboot:
$ uname -mrs
Sample outputs:

Linux 4.19 x86_64

Conclusion

Configurations! You completed various steps to build the Linux kernel from source code. I strongly suggest that you always keep backup of essential data and visit the kernel.org page here for more info.

https://vitux.com/how-to-change-your-ubuntu-computer-name-hostname

How to Change your Ubuntu Computer Name (Hostname)

What is a computer name (hostname)?

Your computer name, in technical terms, is also referred to as the hostname of your computer system. A hostname is how other computers recognize your computer over a local network. Like on the Internet, we have URLs instead of hostnames. These URLs contain regular words like google.com that we can easily understand instead of remembering the numeric IP address of a server.
We can give easy computer name/hostname for our systems so that other computers can easily identify it over a local network. So instead of remembering your IP address, other people can access local web pages and other authorized data on your system through your hostname.
In this article, we will give a few simple ways to change your computer name through the graphical user interface and the command line.
The commands and procedures mentioned in this article have been run on a Ubuntu 18.04 LTS system.

How to change the hostname?

Method 1: Through the GUI

Through the UI, you can change your computer’s device name. It can be called a “pretty hostname” as it is not the permanent or static hostname of your computer. Nevertheless, you can change the device name as follows:
Open your system settings either by clicking the downward arrow located at the top-right corner of your Ubuntu screen and then clicking the settings icon from the following view:

OR
Open the Settings utility through the system Dash as follows:

The Settings utility will by default open in the Wi-Fi view as follows:

Move to the Details view by clicking the Details tab from the left pane. You will be able to view the Device name in the About view as follows:

The device name will change as soon as you enter a new name in the Device name textbox.
Please note that this is not your computer’s permanent hostname. Please read further in this article to view how you can change your computer’s permanent hostname.

Method 2: Manually through the hostname and hosts file

You can view the hostname of your computer by entering the following command in your Terminal:
(Click the Ctrl+Alt+T shortcut to open the Terminal application)

$ hostname

One way to change the hostname is through the following command:
$ sudo hostname new-hostname
Example:

$ sudo hostname Linux-system

The drawbackof this method is that the hostname will revert to the original when you restart your system.
The proper way to change the hostname is by changing it in two configuration files named the hostname and hosts file located in the /etc/ folder.
You can open these files through any of your favorite text editors. We are opening this file in the nano editor as follows:

$ sudo nano /etc/hostname

The only text in this file lists the hostname of your computer. Simply change the text to a new hostname and then exit and save the file by clicking Ctrl+X, and then y and hit enter.
Then open the hosts file as follows:

$ sudo nano /etc/hostname

In this file, the hostname is listed against the IP: 127.0.1.1

Change this hostname to a new hostname and then exit and save the file by clicking Ctrl+X, and then y and hit enter.
Now when you restart the system, your hostname will change to a static new hostname.

Method 3: Through the hostnamectl command

The smartest way to change your hostname is through the hostnamectl command that is a part of the Systemd utility. If Systemd is not already installed on your system, you can install it through the following command as root:

$ sudo apt install systemd

You can check the version number of the Systemd utility by running the following command:

$ systemd --version

This command will give you the version number of the utility and also ensure that it is indeed installed on your system
Now that the Systemd utility is installed on your system, you can run the following command in order to view detailed information about your system, including the hostname:

$ hostnamectl

In this output, the Static hostname lists the permanent hostname of your machine. The Pretty hostname lists the Device name you have set up through the UI in the Settings utility. The hostnamectl lists the Pretty hostname(device name) only if it is different from the static hostname.
In order to change your computer’s hostname through the hostnamectl command, use the following syntax:
$ hostnamectl set-hostname “new-hostname”
Example:

$ hostnamectl set-hostname Linux-system

Now when you see, the hostname through the hostnamectl command, it will show the static hostname as the new hostname you have set. The system has also changed the device name to the hostname you specified through the set-hostname command.
You can verify through the UI that your device name will also be the same as your static hostname. Open the Settings utility and move to the Details tab to view your device name.

The plus point of the Hostnamectl command is that you do not need to restart your computer in order to permanently change the hostname.

Conclusion

Through this tutorial, you learned to change the device name and computer name(hostname) of your system. Now you can change your computer’s hostname either temporarily or permanently through the Ubuntu command line. All you need to do is change a few configuration files or simply use the hostnamectl command to do so. Now you can have a customized computer name through which other computers over the local area will identify you.

https://linuxize.com/post/how-to-set-up-ssh-keys-on-debian-9

How to Set Up SSH Keys on Debian 9

Contents

• • Creating SSH keys on Debian
  • Copy the Public Key to the Server
  • Login to the Server using SSH Keys
  • Disabling SSH Password Authentication
  • Conclusion

Secure Shell (SSH) is a cryptographic network protocol used for secure connection between a client and a server and supports various authentication mechanisms.

The two most popular mechanisms are passwords based authentication and public key based authentication. Using SSH keys is more secure and convenient than traditional password authentication.
In this tutorial we will describe how to generate SSH keys on Debian 9 systems. We will also show you how to setup a SSH key-based authentication and connect to your remote Linux servers without entering a password.

Creating SSH keys on Debian

Before generating a new SSH key pair, first check for existing SSH keys on your Debian client machine. You can do that by running the following command:

ls -l ~/.ssh/id_*.pub

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If the output of the command above contains something like No such file or directory or no matches found it means that you don’t have SSH keys and you can continue with the next step and generate a new SSH key pair.
If there are existing keys, you can either use those and skip the next step or backup up the old keys and generate new ones.
Start by generating a new 4096 bits SSH key pair with your email address as a comment using the following command:

ssh-keygen -t rsa -b 4096 -C "your_email@domain.com"

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The output will look similar to the following:

Enter file in which to save the key (/home/yourusername/.ssh/id_rsa):

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Press Enter to accept the default file location and file name.
Next, you’ll be prompted to type a secure passphrase. Whether you want to use passphrase its up to you. With passphrase, an extra layer of security is added to your key.

Enter passphrase (empty for no passphrase):

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If you don’t want to use passphrase just press Enter
The whole interaction looks like this:

To verify that the SSH key pair was generated, type:

ls ~/.ssh/id_*

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The output should look something like this:

/home/yourusername/.ssh/id_rsa /home/yourusername/.ssh/id_rsa.pub

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Copy the Public Key to the Server

Now that you have your SSH key pair, the next step is to copy the public key to the server you want to manage.
The easiest and the recommended way to copy the public key to the remote server is to use the ssh-copy-id tool.
On your local machine terminal tun the following command:

ssh-copy-id remoteusername@server_ip_address

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You will be prompted to enter the remoteusername password:

remoteusername@server_ip_address's password:

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Once the user is authenticated, the public key ~/.ssh/id_rsa.pub will be appended to the remote user ~/.ssh/authorized_keys file and connection will be closed.

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'username@server_ip_address'"
and check to make sure that only the key(s) you wanted were added.

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If the ssh-copy-id utility is not available on your local computer you can use the following command to copy the public key:

cat ~/.ssh/id_rsa.pub | ssh remoteusername@server_ip_address "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"

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Login to the Server using SSH Keys

At this point you should be able login to the remote server without being prompted for a password.
To test it, try to connect to the server via SSH:

ssh remoteusername@server_ip_address

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If you haven’t set a passphrase, you will be logged in immediately. Otherwise you will be prompted to enter the passphrase.

Disabling SSH Password Authentication

To add an extra layer of security to your server you can disable the password authentication for SSH.
Before disabling SSH password authentication make sure you can login to your server without a password and the user you are logging in with has sudo privileges.
Log into your remote server:

ssh sudo_user@server_ip_address

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Open the SSH configuration file /etc/ssh/sshd_config:

sudo nano /etc/ssh/sshd_config

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Search for the following directives and modify as it follows:

/etc/ssh/sshd_config

PasswordAuthentication no
ChallengeResponseAuthentication no
UsePAM no

Once you are done save the file and restart the SSH service using the following command:

sudo systemctl restart ssh

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At this point, the password based authentication is disabled.

Conclusion

In this tutorial you have learned how to generate a new SSH key pair and setup a SSH key-based authentication. You can add the same key to multiple remote serves.
We have also shown you how to disable SSH password authentication and add an extra layer of security to your server.
If you have any question or feedback feel free to leave a comment.

Kali Linux: What You Must Know Before Using it

https://fosspost.org/articles/must-know-before-using-kali-linux

Kali Linux is the industry’s leading Linux distribution in penetration testing and ethical hacking. It is a distribution that comes shipped with tons and tons of hacking and penetration tools and software by default, and is widely recognized in all parts of the world, even among Windows users who may not even know what Linux is.
Because of the latter, many people are trying to get alone with Kali Linux although they don’t even understand the basics of a Linux system. The reasons may vary from having fun, faking being a hacker to impress a girlfriend or simply trying to hack the neighbors’ WiFi network to get a free Internet, all of which is a bad thing to do if you are planning to use Kali Linux.
Here are some tips that you should know before even planning to use Kali Linux

Kali Linux is Not for Beginners

Kali Linux Default GNOME Desktop

If you are someone who has just started to use Linux few months ago, or if you are don’t consider yourself to be above average in terms of knowledge, then Kali Linux is not for you. If you are going to ask stuff like “How do I install Steam on Kali? How do I make my printer work on Kali? How do I solve the APT sources error on Kali”? Then Kali Linux is not suitable for you.
Kali Linux is mainly made for professionals wanting to run penetration testing suits or people who want to learn ethical hacking and digital forensics. But even if you were from the latter, the average Kali Linux user is expected to face a lot of trouble while using Kali Linux for his day-to-day usage. He’s also expected to take a very careful approach to how he uses the tools and software, it’s not just “let’s install it and run everything”. Every tool must be carefully used, every software you install must be carefully examined.
Good Read: What are the components of a Linux system?
Stuff which the average Linux user can’t do normally. A better approach would be to spend few weeks learning about Linux and its daemons, services, software, distributions and the way it works, and then watch few dozens of videos and courses about ethical hacking, and only then, try to use Kali to apply what you learned.

it Can Get You Hacked

Kali Linux Hacking & Testing Tools

In a normal Linux system, there’s one account for normal user and one separate account for root. This is not the case in Kali Linux. Kali Linux uses the root account by default and doesn’t provide you with a normal user account. This is because almost all security tools available in Kali do require root privileges, and to avoid asking you for root password every minute, they designed it that way.
Of course, you could simply create a normal user account and start using it. Well, it’s still not recommended because that’s not how the Kali Linux system design is meant to work. You’ll face a lot of problems then in using programs, opening ports, debugging software, discovering why this thing doesn’t work only to discover that it was a weird privilege bug. You will also be annoyed by all the tools that will require you to enter the password each time you try to do anything on your system.
Now, since you are forced to use it in as a root user, all the software you run on your system will also run with root privileges. This is bad if you don’t know what you are doing, because if there’s a vulnerability in Firefox for example and you visit one of the infected dark web sites, the hacker will be able to get full root permissions on your PC and hack you, which would have been limited if you were using a normal user account. Also, some tools that you may install and use can open ports and leak information without your knowledge, so if you are not extremely careful, people can hack you in the same way you may try to hack them.
If you visit Facebook groups related to Kali Linux on few occasions, you’ll notice that almost a quarter of the posts in these groups are people calling for help because someone hacked them.

it Can Get You in Jail

Kali Linux provide the software as it is. Then, it is your own responsibility alone of how you use them.
In most advanced countries around the world, using penetration testing tools against public WiFi networks or the devices of others can easily get you in jail. Now don’t think that you can’t be tracked just because you are using Kali, many systems are configured to have complex logging devices to simply track whoever tries to listen or hack their networks, and you may stumble upon one of these, and it will destroy you life.
Don’t ever use Kali Linux tools against devices/networks which do not belong to you or given explicit permission to try hacking them. If you say that you didn’t know what you were doing, it won’t be accepted as an excuse in a court.

Modified Kernel and Software

Kali is based on Debian (Testing branch, which means that Kali Linux uses a rolling release model), so it uses most of the software architecture from there, and you will find most of the software in Kali Linux just as they are in Debian.
However, some packages were modified to harden security and fix some possible vulnerabilities. The Linux kernel that Kali uses for example is patched to allow wireless injection on various devices. These patches are not normally available in the vanilla kernel. Also, Kali Linux does not depend on Debian servers and mirrors, but builds the packages by its own servers. Here’s the default software sources in the latest release:

deb http://http.kali.org/kali kali-rolling main contrib non-free
deb-src http://http.kali.org/kali kali-rolling main contrib non-free

That’s why, for some specific software, you will find a different behaviour when using the same program in Kali Linux or using it in Fedora, for example. You can see a full list of Kali Linux software from git.kali.org. You can also find our own generated list of installed packages on Kali Linux (GNOME).
More importantly, Kali Linux official documentation extremely suggests to NOT add any other 3rd-party software repositories, because since Kali Linux is a rolling release and depends on Debian Testing, you will most likely break your system by just adding a new repository source due to dependencies conflicts and package hooks.

Don’t Install Kali Linux

Running wpscan on fosspost.org using Kali Linux

I use Kali Linux on rare occasions to test the software and servers I deploy. However, I will never dare to install it and use it as a primary system.
If you are going to use it as a primary system, then you will have to keep your own personal files, password, data and everything else on your system. You will also need to install tons of daily-use software in order to ease your life. But as we mentioned above, using Kali Linux is very risky and should be done very carefully, and if you get hacked, you will lose all your data and it may get exposed to a wider audience. Your personal information can also be used to track you if you are doing non-legal stuff. You may even destroy your data by yourself if you are not careful about how you use the tools.
Even professional white hackers don’t recommend installing it as a primary system, but rather, use it from USB to just do your penetration testing work and then leave back to your normal Linux distribution.

The Bottom Line

As you may see now, using Kali is not an easy decision to take lightly. If you are planning to be a whiter hacker and you need to use Kali to learn, then go for it after learning the basics and spending few months with a normal system. But be careful for what you are doing to avoid being in trouble.
If you are planning to use Kali or if you need any help, I’ll be happy to hear your thoughts in the comments.

How to use arrays in bash script

https://linuxconfig.org/how-to-use-arrays-in-bash-script

Objective

After following this tutorial you should be able to understand how bash arrays work and how to perform the basic operations on them.

Requirements

• No special system privileges are required to follow this tutorial

Difficulty

EASY

Introduction

Bash, the Bourne Again Shell, it's the default shell on practically all major linux distributions: it is really powerful and can be also considered as a programming language, although not as sophisticated or feature-reach as python or other "proper" languages. In this tutorial we will see how to use bash arrays and perform fundamental operations on them.

Create an array

The first thing to do is to distinguish between bash indexed array and bash associative array. The former are arrays in which the keys are ordered integers, while the latter are arrays in which the keys are represented by strings. Although indexed arrays can be initialized in many ways, associative ones can only be created by using the declare command as we will see in a moment.

---

---

Create indexed or associative arrays by using declare

We can explicitly create an array by using the declare command:

$ declare -a my_array

Declare, in bash, it's used to set variables and attributes. In this case, since we provided the -a option, an indexed array has been created with the "my_array" name.

Associative arrays can be created in the same way: the only thing we need to change is the option used: instead of lowercase -a we must use the -A option of the declare command:

$ declare -A my_array

This, as already said, it's the only way to create associative arrays in bash.

Create indexed arrays on the fly

We can create indexed arrays with a more concise syntax, by simply assign them some values:

$ my_array=(foo bar)

In this case we assigned multiple items at once to the array, but we can also insert one value at a time, specifying its index:

$ my_array[0]=foo

Array operations

Once an array is created, we can perform some useful operations on it, like displaying its keys and values or modifying it by appending or removing elements:

Print the values of an array

To display all the values of an array we can use the following shell expansion syntax:

${my_array[@]}

Or even:

${my_array[*]}

Both syntax let us access all the values of the array and produce the same results, unless the expansion it's quoted. In this case a difference arises: in the first case, when using @, the expansion will result in a word for each element of the array. This becomes immediately clear when performing a for loop. As an example, imagine we have an array with two elements, "foo" and "bar":

$ my_array=(foo bar)

Performing a for loop on it will produce the following result:

$ for i in "${my_array[@]}"; do echo "$i"; done
foo
bar

When using *, and the variable is quoted, instead, a single "result" will be produced, containing all the elements of the array:

$ for i in "${my_array[*]}"; do echo "$i"; done
foo bar

---

---

Print the keys of an array

It's even possible to retrieve and print the keys used in an indexed or associative array, instead of their respective values. The syntax is almost identical, but relies on the use of the ! operator:

$ my_array=(foo bar baz)
$ for index in "${!my_array[@]}"; do echo "$index"; done
0
1
2

The same is valid for associative arrays:

$ declare -A my_array
$ my_array=([foo]=bar [baz]=foobar)
$ for key in "${!my_array[@]}"; do echo "$key"; done
baz
foo

As you can see, being the latter an associative array, we can't count on the fact that retrieved values are returned in the same order in which they were declared.

Getting the size of an array

We can retrieve the size of an array (the number of elements contained in it), by using a specific shell expansion:

$ my_array=(foo bar baz)
$ echo "the array contains ${#my_array[@]} elements"
the array contains 3 elements

We have created an array which contains three elements, "foo", "bar" and "baz", then by using the syntax above, which differs from the one we saw before to retrieve the array values only for the # character before the array name, we retrieved the number of the elements in the array instead of its content.

Adding elements to an array

As we saw, we can add elements to an indexed or associative array by specifying respectively their index or associative key. In the case of indexed arrays, we can also simply add an element, by appending to the end of the array, using the += operator:

$ my_array=(foo bar)
$ my_array+=(baz)

If we now print the content of the array we see that the element has been added successfully:

$ echo "${my_array[@]}"
foo bar baz

Multiple elements can be added at a time:

$ my_array=(foo bar)
$ my_array+=(baz foobar)
$ echo "${my_array[@]}"
foo bar baz foobar

To add elements to an associative array, we are bound to specify also their associated keys:

$ declare -A my_array

# Add single element
$ my_array[foo]="bar"

# Add multiple elements at a time
$ my_array+=([baz]=foobar [foobarbaz]=baz)

---

---

Deleting an element from the array

To delete an element from the array we need to know it's index or its key in the case of an associative array, and use the unset command. Let's see an example:

$ my_array=(foo bar baz)
$ unset my_array[1]
$ echo ${my_array[@]}
foo baz

We have created a simple array containing three elements, "foo", "bar" and "baz", then we deleted "bar" from it running unset and referencing the index of "bar" in the array: in this case we know it was 1, since bash arrays start at 0. If we check the indexes of the array, we can now see that 1 is missing:

$ echo ${!my_array[@]}
0 2

The same thing it's valid for associative arrays:

$ declare -A my_array
$ my_array+=([foo]=bar [baz]=foobar)
$ unset my_array[foo]
$ echo ${my_array[@]}
foobar

In the example above, the value referenced by the "foo" key has been deleted, leaving only "foobar" in the array.

Deleting an entire array, it's even simpler: we just pass the array name as an argument to the unset command without specifying any index or key:

$ unset my_array
$ echo ${!my_array[@]}

After executing unset against the entire array, when trying to print its content an empty result is returned: the array doesn't exist anymore.

Conclusions

In this tutorial we saw the difference between indexed and associative arrays in bash, how to initialize them and how to perform fundamental operations, like displaying their keys and values and appending or removing items. Finally we saw how to unset them completely. Bash syntax can sometimes be pretty weird, but using arrays in scripts can be really useful. When a script starts to become more complex than expected, my advice is, however, to switch to a more capable scripting language such as python.

Have a Plan for Netplan

https://www.linuxjournal.com/content/have-plan-netplan

by Shawn Powers

on October 16, 2018

Ubuntu changed networking. Embrace the YAML.
If I'm being completely honest, I still dislike the switch from eth0, eth1, eth2 to names like, enp3s0, enp4s0, enp5s0. I've learned to accept it and mutter to myself while I type in unfamiliar interface names. Then I installed the new LTS version of Ubuntu and typed vi /etc/network/interfaces. Yikes. After a technological lifetime of entering my server's IP information in a simple text file, that's no longer how things are done. Sigh. The good news is that while figuring out Netplan for both desktop and server environments, I fixed a nagging DNS issue I've had for years (more on that later).

The Basics of Netplan

The old way of configuring Debian-based network interfaces was based on the ifupdown package. The new default is called Netplan, and although it's not terribly difficult to use, it's drastically different. Netplan is sort of the interface used to configure the back-end dæmons that actually configure the interfaces. Right now, the back ends supported are NetworkManager and networkd.
If you tell Netplan to use NetworkManager, all interface configuration control is handed off to the GUI interface on the desktop. The NetworkManager program itself hasn't changed; it's the same GUI-based interface configuration system you've likely used for years.
If you tell Netplan to use networkd, systemd itself handles the interface configurations. Configuration is still done with Netplan files, but once "applied", Netplan creates the back-end configurations systemd requires. The Netplan files are vastly different from the old /etc/network/interfaces file, but it uses YAML syntax, and it's pretty easy to figure out.

The Desktop and DNS

If you install a GUI version of Ubuntu, Netplan is configured with NetworkManager as the back end by default. Your system should get IP information via DHCP or static entries you add via GUI. This is usually not an issue, but I've had a terrible time with my split-DNS setup and systemd-resolved. I'm sure there is a magical combination of configuration files that will make things work, but I've spent a lot of time, and it always behaves a little oddly. With my internal DNS server resolving domain names differently from external DNS servers (that is, split-DNS), I get random lookup failures. Sometimes ping will resolve, but dig will not. Sometimes the internal A record will resolve, but a CNAME will not. Sometimes I get resolution from an external DNS server (from the internet), even though I never configure anything other than the internal DNS!
I decided to disable systemd-resolved. That has the potential to break DNS lookups in a VPN, but I haven't had an issue with that. With resolved handling DNS information, the /etc/resolv.conf file points to 127.0.0.53 as the nameserver. Disabling systemd-resolved will stop the automatic creation of the file. Thankfully, NetworkManager itself can handle the creation and modification of /etc/resolv.conf. Once I make that change, I no longer have an issue with split-DNS resolution. It's a three-step process:

1. Do sudo systemctl disable systemd-resolved.service.
2. Then sudo rm /etc/resolv.conf (get rid of the symlink).
3. Edit the /etc/NetworkManager/NetworkManager.conf file, and in the [main] section, add a line that reads DNS=default.

Once those steps are complete, NetworkManager itself will create the /etc/resolv.conf file, and the DNS server supplied via DHCP or static entry will be used instead of a 127.0.0.53 entry. I'm not sure why the resolved dæmon incorrectly resolves internal addresses for me, but the above method has been foolproof, even when switching between networks with my laptop.

Netplan CLI Configuration

If Ubuntu is installed in server mode, it is almost certainly configured to use networkd as the back end. To check, have a look at the /etc/netplan/config.yaml file. The renderer should be set to networkd in order to use the systemd-networkd back end. The file should look something like this:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp2s0:
      dhcp4: true

Important note: remember that with YAML files, whitespace matters, so the indentation is important. It's also very important to remember that after making any changes, you need to run sudo netplan apply so the back-end configuration files are populated.
The default renderer is networkd, so it's possible you won't have that line in your configuration file. It's also possible your configuration file will be named something different in the /etc/netplan folder. All .conf files are read, so it doesn't matter what it's called as long as it ends with .conf. Static configurations are fairly simple to set up:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp2s0:
      dhcp4: no
      addresses:
        - 192.168.1.10/24
        - 10.10.10.10/16
      gateway4: 192.168.1.1
      nameservers:
        addresses: [192.168.1.1, 8.8.8.8]

Notice I've assigned multiple IP addresses to the interface. Netplan does not support virtual interfaces like enp3s0:0, rather multiple IP addresses can be assigned to a single interface.
Unfortunately, networkd doesn't create an /etc/resolv.conf file if you disable the resolved dæmon. If you have problems with split-DNS on a headless computer, the best solution I've come up with is to disable systemd-resolved and then manually create an /etc/resolv.conf file. Since headless computers don't usually move around as much as laptops, it's likely the /etc/resolv.conf file won't need to be changed. Still, I wish networkd had an option to manage the resolv.conf file the same way NetworkManager does.

Advanced Network Configurations

The configuration formats are different, but it's still possible to do more advanced network configurations with Netplan:
Bonding:

network:
  version: 2
  renderer: networkd
  bonds:
    bond0:
      dhcp4: yes
      interfaces:
        - enp2s0
        - enp3s0
      parameters:
        mode: active-backup
        primary: enp2s0

The various bonding modes (balance-rr, active-backup, balance-xor, broadcast, 802.3ad, balance-tlb and balance-alb) are supported.
Bridging:

network:
  version: 2
  renderer: networkd
  bridges:
    br0:
      dhcp4: yes
      interfaces:
        - enp4s0
        - enp3s0

Bridging is even simpler to set up. This configuration creates a bridge device using the two interfaces listed. The device (br0) gets address information via DHCP.

CLI Networking Commands

If you're a crusty old sysadmin like me, you likely type ifconfig to see IP information without even thinking. Unfortunately, those tools are not usually installed by default. This isn't actually the fault of Ubuntu and Netplan; the old ifconfig toolset has been deprecated. If you want to use the old ifconfig tool, you can install the package:

sudo apt install net-tools

But, if you want to do it the "correct" way, the new "ip" tool is the proper way to do it. Here are some equivalents of things I commonly do with ifconfig:
Show network interface information.
Old way:

ifconfig

New way:

ip address show

(Or you can just do ip a, which is actually less typing than ifconfig.)
Bring interface up.
Old way:

ifconfig enp3s0 up

New way:

ip link set enp3s0 up

Assign IP address.
Old way:

ifconfig enp3s0 192.168.1.22

New way:

ip address add 192.168.1.22 dev enp3s0

Assign complete IP information.
Old way:

ifconfig enp3s0 192.168.1.22 net mask 255.255.255.0 broadcast
 ↪192.168.1.255

New way:

ip address add 192.168.1.22/24 broadcast 192.168.1.255
 ↪dev enp3s0

Add alias interface.
Old way:

ifconfig enp3s0:0 192.168.100.100/24

New way:

ip address add 192.168.100.100/24 dev enp3s0 label enp3s0:0

Show the routing table.
Old way:

route

New way:

ip route show

Add route.
Old way:

route add -net 192.168.55.0/24 dev enp4s0

New way:

ip route add 192.168.55.0/24 dev enp4s0

Old Dogs and New Tricks

I hated Netplan when I first installed Ubuntu 18.04. In fact, on the particular server I was installing, I actually started over and installed 16.04 because it was "comfortable". After a while, curiosity got the better of me, and I investigated the changes. I'm still more comfortable with the old /etc/network/interfaces file, but I have to admit, Netplan makes a little more sense. There is a single "front end" for configuring networks, and it uses different back ends for the heavy lifting. Right now, the only back ends are the GUI NetworkManager and the systemd-networkd dæmon. With the modular system, however, that could change someday without the need to learn a new way of configuring interfaces. A simple change to the renderer line would send the configuration information to a new back end.
With regard to the new command-line networking tool (ip vs. ifconfig), it really behaves more like other network devices (routers and so on), so that's probably a good change as well. As technologists, we need to be ready and eager to learn new things. If we weren't always trying the next best thing, we'd all be configuring Trumpet Winsock to dial in to the internet on our Windows 95 machines. I'm glad I tried that new Linux thing, and while it wasn't quite as dramatic, I'm glad I tried Netplan as well!