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.