Rotating screen in Linux Desktop

Sometimes we need to capture an output of a command that is quite long, it could not fit in one screenshot. Rotating screen is one of the way to make the screen estate longer, but in linux, the method is not as straight forward as in our smartphones.

To do this, one of the method is using "xrandr" command. 

The usage is fairly simple, just use xrandr with "-o" option, and which way we want to rotate the screen to.

For example, to rotate the screen left, we use:

$ xrandr -o left

To rotate the screen to right:

$ xrandr -o right

To invert the screen:

$ xrandr -o inverted

To rotate the screen back to its normal position:

$ xrandr -o normal

Do not worry though, only the screen is rotated, your keyboard and mouse still work the same.

Installing docker and docker compose on almalinux 9

Docker does not explicitly support almalinux, so we have to use centos repository instead.

Below are the steps:

1. Update system

sudo dnf --refresh update

sudo dnf upgrade -y

2. Enable docker repository

sudo dnf install yum-utils

sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo

3. Install docker

sudo dnf install docker-ce docker-ce-cli containerd.io docker-compose-plugin -y

4. Enable and start docker

sudo systemctl enable --now docker

5. Add user to docker group

sudo usermod -G docker -a myuser

6. Refresh group list 

newgrp

7. Check docker and docker compose version

docker version

docker compose version          

Linux Mint unable to connect to 2.4GHz wireless, but no problem connecting to 5GHz wireless

I have this issue whereby a laptop of mine, which is running Linux Mint 21.2, was unable to connect to my 2.4GHz wife connection. I have no issue connecting to the 5GHz connection, only 2.4Ghz is having issue. I turned to linux mint forum, and found this post, which explained the issue, and the solution was to change my backend wifi device from wpa-supplicant to iwd. It seems that the current wifi daemon at that time, which was wpasupplicant was having issue connecting to 2.4GHz wifi connection. 

Here are the steps:

1. Install iwd

sudo apt update && sudo apt install iwd -y

2. Create a configuration file in /etc/NetworkManager/conf.d/wifi-backend.conf 

sudo nano /etc/NetworkManager/conf.d/wifi-backend.conf 

3. Add in below setting

[device]

wifi.backend=iwd

4. Save and exit nano by pressing ctrl-o and then ctrl-x

5. Stop and disable wpa_supplicant daemon

sudo systemctl disable --now wpa_supplicant

6. Start and enable iwd

sudo systemctl enable --now iwd

7. Restart NetworkManager daemon

sudo systemctl restart NetworkManager

And you are good  to go. You should now be able to connect to the 2.4GHz wireless, without any issue. 

Linux Container (LXC) 101

LXC is a userspace interface for the Linux kernel containment features. Through a powerful API and simple tools, it lets users easily create and manage system or application containers.

The main usage of LXC in my scenario is, to test out any application in linux before deploying to the real environment, without disturbing my host linux. I used to use virtualbox, but LXC is lighter in terms of resources usage, but only applicable to linux. 

To install lxc in an ubuntu machine:

$ sudo apt update && sudo apt install lxc -y

Once installed, you now have access to multiple lxc-* commands. 

If our ufw firewall is turned on, we need to allow traffic to and from the bridge, and also allow traffic forwarded to the bridge. The name of the bridge is usually lxcbr0

$ sudo ufw allow in on lxcbr0

$ sudo ufw route allow in on lxcbr0

$ sudo ufw route allow out on lxcbr0

To create a container, use lxc-create command. For example, to create a container named as u1, using a template from https://images.linuxcontainers.org/, in an interactive mode (where you get to select distribution, release and architecture interactively), use below command

$ sudo lxc-create -n u1 -t download

To create a same almalinux container, named u2, using a template from https://images.linuxcontainers.org/ but in a non interactive mode, use below command

$ sudo lxc-create -n u2 -t download -- -d almalinux -r 8 -a amd64 

To list out all created containers, use below command 

$ sudo lxc-ls

To get a better listing, use fancy mode (-f)

$ sudo lxc-ls -f

To start the containers, just use lxc-start

$ sudo lxc-start u1

$ sudo lxc-start u2

After a while, the containers will get ip addresses

To access the shell of the containers, we use lxc-attach

$ sudo lxc-attach u1

To exit the shell, just type exit

To destroy the containers, we need to stop the container first.

$ sudo lxc-stop u1

$ sudo lxc-destroy u1

Multiple ways to extract zip files in linux terminal

I downloaded a big zip file (5.9GB) for an application, and as usual, to unzip it, just use unzip command.

$ unzip mybigfile.zip

I received this error, which is unusual.

Error when extracting using unzip command

Then I search around to find any other zip application that can extract the file. I am pretty confident that file is fine, since the provider has provided a md5sum file, and it matches. I ended up trying "jar" command. To install jar in ubuntu, simply run below command:

$ sudo apt update && sudo apt install fastjar -y

Once installed, extract the zip file using below command

$ jar xvf mybigfile.zip

Unfortunately, jar is also unable to extract the file, with below error:

Error when extracting using jar command

The I encounter another robust archiver called 7z, which can be installed in ubuntu using below command:

$ sudo apt update && sudo apt install 7zip -y

To extract a zip file, simply run this command:

$ 7z x mybigfile.zip

Even though 7z reported some error as well, but it managed to extract the file. 

Error when extracting using 7z command

There you go, 3 commands to extract a zip file. So do not worry if you are unable to extract any zip file, you can always try a few commands to get the job done.