RHCSA v8: What's New

Linux RedHat RHCSA

The updated RHCSA exam for RHEL 8 has been out since last year, however, the old exam is still available, and will stay available until August 1st, 2020:



You may be trying to figure out what version will be best for you, and I’m hoping the information here will help you.

Something to take in consideration is that the exam is valid for 3 years, or 2 releases (meaning that once RHEL 9 is out, your RHSCA on RHEL 7 is no longer valid). And seeing on how RHEL 6 to 7 took 4 years, and RHEL 7 to 8 took 5 years, with RHCSA v7 you will most likely run out of the 3 years before RHEL 9 is released.

Objective Differences - RHCSA v7 vs v8

=> RHCSA v7 - Content No Longer Needed for V8

Operate running systems

  • Access a virtual machine’s console.
  • Start and stop virtual machines.

Create and configure file systems

  • Mount and unmount CIFS and NFS network file systems.
    • CIFS is no longer covered
  • Create and manage Access Control Lists (ACLs).
    • Looks like this is still in the exam, but under “Manage Security => Create and use file access control lists”

Deploy, configure, and maintain systems

  • Install Red Hat Enterprise Linux systems as virtual guests.
  • Configure systems to launch virtual machines at boot.
  • Configure a system to use time services.
  • Update the kernel package appropriately to ensure a bootable system.

Manage users and groups

  • Configure a system to use an existing authentication service for user and group information.

Manage security

  • Configure firewall settings using firewall-config, firewall-cmd, or iptables.
    • iptables is no longer covered

=> RHCSA v8 - New Content

Operate running systems

  • Preserve system journals

Create and configure file systems

  • Configure disk compression
  • Manage layered storage

Deploy, configure, and maintain systems

  • Configure time service clients
    • Red Hat doesn’t ask candidates to set up time service client and server anymore but only time service clients. Knowledge of the NTP daemon is no longer necessary, that of Chrony is enough.
  • Work with package module streams

Manage basic networking

  • Configure IPv4 and IPv6 addresses

Manage users and groups

  • Configure superuser access

References:

Bash Arrays and Iterations

Bash Linux

Bash arrays can be great for iterating over a list of items. I’m giving a quick example below on a list of services. All you need is to list all values in different arrays and use an index to map them back together.

Example:

# Service Path Config File
1 CUPS /etc/cups cupsd.conf
2 MPD /etc mpd.conf
3 SSHD /etc/ssh sshd.conf
4 DHCPD /etc dhcpd.conf

Let’s break down our columns into arrays:

service_arr=(
  CUPS
  MPD
  SSHD
  DHCPD
)

path_arr=(
  /etc/cups
  /etc
  /etc
  /etc
)

config_file_arr=(
  cupsd.conf
  mpd.conf
  sshd.conf
  dhcpd.conf
)

Now to iterate through our items, let’s make sure we start at index 1 and add at each run:

cnt=1

for i in ${!service_arr[@]} ; do
  echo "The configuration file for the service ${service_arr[$i]} is ${path_arr[$i]}/${config_file_arr[$i]}"
  let count+=1
done

The result is:

The configuration file for the service CUPS is /etc/cups/cupsd.conf
The configuration file for the service MPD is /etc/mpd.conf
The configuration file for the service SSHD is /etc/sshd.conf
The configuration file for the service DHCPD is /etc/dhcpd.conf

You can also use especial characters (like * when searching for files and using shell expansion). Just make sure to properly quote them.

Touchpad Gestures on XPS 13

Hardware Linux

The XPS 13 is a great laptop and it comes with an equally matched touchpad. Setting up touch gestures is pretty easy, and we will cover what needs to be done to get it working on Arch.

First, let’s install all the needed software:

  • extra/libinput
  • aur/libinput-gestures

After installing the 2 packages you should be able to run libinput-gestures -d as root and try the pre-defined gestures. You should see an output when you swipe left/right/up/down with ¾ fingers and pinch in/out.

# libinput-gestures -d

libinput-gestures: session unknown+unknown on Linux-5.0.6-arch1-1-ARCH-x86_64-with-arch, python 3.7.3, libinput 1.13.0
/usr/bin/libinput-gestures: hash 4cc3250c5befc6926c04b3e499114677
Gestures configured in /etc/libinput-gestures.conf:
swipe up           _internal ws_up
swipe down         _internal ws_down
swipe left         xdotool key alt+Right
swipe right        xdotool key alt+Left
pinch in           xdotool key super+s
pinch out          xdotool key super+s
libinput-gestures: device /dev/input/event10: DLL075B:01 06CB:76AF Touchpad
libinput-gestures: SWIPE up 3 [-33.88000000000001, -604.8000000000001]
   _internal ws_up
libinput-gestures: SWIPE right 3 [755.69, -17.479999999999993]
   xdotool key alt+Left

Let’s add your user to the input group (because it should not run as root), then re-login:

sudo gpasswd -a [user] input

Now let’s edit our personal config file in ~/.config/libinput-gestures.conf. Using xdotool create a map of what keyboard shortcuts you would like to map your gestures to. Keep in mind you can also map it to commands.

For example, my config file looks like this:

# Gestures
gesture swipe up 3 xdotool key Ctrl+F9
gesture swipe up 4 xdotool key Ctrl+F10
gesture swipe left 3 xdotool key Ctrl+Alt+Right
gesture swipe right 3 xdotool key Ctrl+Alt+Left
gesture swipe down 3 xdotool key Super+Down

And the keyboard shortcuts are mapped to (KDE):

  • Ctrl+F9 - Show all windows (current desktop)
  • Ctrl+F10 - Show all windows (all desktops)
  • Ctrl+Alt+Right - Move to desktop on right
  • Ctrl+Alt+Left - Move to desktop on left
  • Super+Down - Desktop preview

Let’s configure the gestures to start with the desktop environment:

$ libinput-gestures-setup autostart

And start the gestures for the current session:

$ libinput-gestures-setup start

Icon theme "papirus" not found.
Icon theme "ubuntu-mono-dark" not found.
Icon theme "Mint-X" not found.
Icon theme "elementary" not found.
Icon theme "gnome" not found.
libinput-gestures started.

Enjoy your new setup gestures.

Bash Tips: History

Linux Bash

Bash keeps a history of the commands you type in and saves them to ~/.bash_history. These commands can be accessed in many ways and there are a lot of configuration related on how they are saved. I’ll cover some basic functionality here.

Event Designators (!, !!, !*)

From MAN Pages

An event designator is a reference to a command line entry in the history list. Unless the reference is absolute, events are relative to the current position in the history list.

For the different examples below, assume we are running it against the same command (netstat -an | grep ':22'). This is to help you visualize the differences between each of the event designators.

Repeating the last command that starts with !string

You can run the most recent command starting with string by using !string.

$ !netstat
netstat -an | grep ':22'
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN     
tcp6       0      0 :::22000                :::*                    LISTEN     
tcp6       0      0 :::22

Another example:

$ ls my_file.txt
.rw-r--r--     0 victor users 18 Oct 11:35  my_file.txt

$ ls my_folder
drwxr-xr-x     - victor users 18 Oct 11:35  my_folder

$ !ls
ls my_folder
drwxr-xr-x     - victor users 18 Oct 11:35  my_folder

Tip: you can use the :p option to print the command instead of running it

$ !netstat:p
netstat -an | grep ':22'

Repeating the same command with !!

As you may already know, the !! can be used for repeating the same command.

$ echo !!
echo netstat -an | grep ':22'

This is useful when you forget to use sudo on a command that requires sudo access.

For example:

$ systemctl daemon-reload
Failed to reload daemon: Access denied

$ sudo !!
sudo systemctl daemon-reload
[sudo] password for victor:

Re-using the last argument with !$

Another very useful option is the !$, which provides quick access to the last argument in a command.

$ echo !$
echo ':22'

This can come in handy if you need to repeat the last argument with another command.

$ touch my_new_script.sh

$ vim !$
vim my_new_script.sh

Another example:

$ mkdir myfolder

$ cd !$

The fc command

The command fc allows you to open commands in your history with an editor, modify the commands and then execute the modified version. It will use your default editor (as per $EDITOR), so make sure that is set.

Some common usage for fc:

  • fc -l - List your last commands
  • fc n - Edit the n command
  • fc -1 - Edit the last command
  • fc 20 22 - Edit commands 20 to 22

History Settings

On this section we talk a little bit about some of the configuration available for your Bash history.

Adds time to each command in history

# Sets up time for history
export HISTTIMEFORMAT="+%Y/%m/%d %T "

For example:

$ history | tail -n 10
  949  +2019/03/11 00:32:53 ssh seedbox
  950  +2019/03/11 16:05:53 cd .config/polybar
  951  +2019/03/11 16:05:56 ./launch.sh
  952  +2019/03/11 17:49:38 lolbanner victor
  953  +2019/03/11 17:53:10 lolbanner test
  954  +2019/03/11 17:53:11 psg checkupdates
  955  +2019/03/11 17:53:11 clear
  956  +2019/03/11 17:53:11 echo hello 1
  957  +2019/03/11 17:53:11 history
  958  +2019/03/11 18:10:01 history | tail -n 10

Avoid duplicate entries

# Avoid duplicates
export HISTCONTROL=ignoredups:erasedups

Append entries

This comes in handy if you run multiple terminal emulators simultaneously. By default, the latest closed terminal emulator will overwrite history from the other windows. With this setting, changes are appended making sure all commands are saved to history.

# When the shell exits, append to the history file instead of overwriting it
shopt -s histappend

Colorful Banners With figlet and lolcat

Linux Bash

Banners in *nix like systems is something that is being used for a very long time. System admins would sometimes use it to let users know that the system was going down (nowadays built-in with the shutdown command), or setup motd messages for SSH logins. Within the past years people got very creative with the use of different fonts and ASCII art.

For today’s post we will work With two different apps to display beautiful banners on your systems or config/dot files:

  • figlet - displays the banners
  • lolcat - colorizes the banners

Installation (Arch)

pacman -Sy figlet lolcat

figlet

Figlet comes with a default font and you can start using it right away

$ figlet "Hello World"
 _   _      _ _        __        __         _     _
| | | | ___| | | ___   \ \      / /__  _ __| | __| |
| |_| |/ _ \ | |/ _ \   \ \ /\ / / _ \| '__| |/ _` |
|  _  |  __/ | | (_) |   \ V  V / (_) | |  | | (_| |
|_| |_|\___|_|_|\___/     \_/\_/ \___/|_|  |_|\__,_|

You can also download additional fonts (which is what we want). This will allow you to create a huge variety of banners.

Head over to the figlet-fonts project and take a look at the font files (*.flf). I would advise downloading the 3d.flf because that’s what we will use here. You can also clone the whole repo.

Place the new font in ~/.local/share/fonts/ and give it as an argument to the -f option in figlet:

$ figlet -f ~/.local/share/fonts/3d.flf "Hello World"
 ██      ██          ██  ██            ██       ██                  ██      ██
░██     ░██         ░██ ░██           ░██      ░██                 ░██     ░██
░██     ░██  █████  ░██ ░██  ██████   ░██   █  ░██  ██████  ██████ ░██     ░██
░██████████ ██░░░██ ░██ ░██ ██░░░░██  ░██  ███ ░██ ██░░░░██░░██░░█ ░██  ██████
░██░░░░░░██░███████ ░██ ░██░██   ░██  ░██ ██░██░██░██   ░██ ░██ ░  ░██ ██░░░██
░██     ░██░██░░░░  ░██ ░██░██   ░██  ░████ ░░████░██   ░██ ░██    ░██░██  ░██
░██     ░██░░██████ ███ ███░░██████   ░██░   ░░░██░░██████ ░███    ███░░██████
░░      ░░  ░░░░░░ ░░░ ░░░  ░░░░░░    ░░       ░░  ░░░░░░  ░░░    ░░░  ░░░░░░

lolcat

Lolcat produces a rainbow effect on terminal text. For example, try listing a directory and then piping it to lolcat. It should produce an output similar to the one below:

Putting it all together

Use the same figlet command we used before to print out “Hello World” and pipe it through lolcat to get the result below:

Optionally, you can add Bash alias/function to quickly display colorized banners:

lolbanner ()
{
    echo
    figlet -f ~/.local/share/fonts/3d.flf $* | lolcat
    echo
}

Have fun adding banners to your dot files, config files and screenshots/videos. Just remember that for config files, the colors will not be saved/shown.

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