Programming/Linux

Linux

Linux is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on 1991.09.17 by Linux Torvalds. Linux is typically packaged in a Linux distribution.

Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project.

Popular Linux distributions include Debian, Fedora, and Ubuntu. Commercial distributions include Red Hat Enterprise Linux and SUSE Linux Enterprise Server.

Learning about the system

Which Linux?

To find out which Linux distribution is running on your machine, you can use

$ hostnamectl
   Static hostname: ip-172-31-24-17
         Icon name: computer-vm
           Chassis: vm
        Machine ID: b54d0220fe634fa4a96fa3d0641ab3ea
           Boot ID: 5208456664c54b09b34be6b541fa7588
    Virtualization: xen
  Operating System: Ubuntu 20.04.1 LTS
            Kernel: Linux 5.4.0-1029-aws
      Architecture: x86-64

More specifically, to find out the Kernel version, you can use

$ uname -r
5.4.0-1029-aws

Working with packages

How to install a package?

Use apt, the command line interface for the package management system.

Before proceeding, run

$ sudo apt update

update is used to download package information from all configured sources. Other commands operate on this data to e.g. perform package upgrades or search in and display details about all packages available for installation.

Once this is done, run

$ sudo apt install emacs

to install the GNU project Emacs editor,

$ sudo apt install mc

to install the GNU Midnight Commander. Other packages are installed in a similar manner.

How to find out which packages can be upgraded?

$ sudo apt list --upgradable

will produce a list of all packages that can be upgraded.

How to upgrade a package?

To upgrade a specific package, say emacs, you can use

sudo apt upgrade emacs

To upgrade all upgradable packages, use

sudo apt upgrade

Working with files and directories

Basics

An *absolute* path is defined as specifying the location of a file or directory from the root directory (/).

What is the current directory?

To find out the current directory on a Linux system, use

$ pwd
/home/ubuntu

How can I change the current directory?

The current directory can be changed using cd, for example:

~$ cd /var/www
/var/www$

To change the current directory to the user's home directory, one can use simply

$ cd

What are the contents of the current directory?

To list the contents of the current directory, you can use ls. In its most basic form, it's simply

$ ls

A useful variant is

$ ls -alt

where -a tells ls not to ignore entries starting with ., -l means that ls should use a long listing format, -t tells is to sort by modification time, newest first. (ls -a -l -t can be compressed into ls -alt.)

Creating an empty file

To create an empty file, you can use touch:

$ touch README.txt

If the file already exists, touch will update its access and modification times to the current time.

DevOps

What is my system currently doing?

To find out what the system is currently doing, including things such as CPU and memory utilization, you can use glances.

To install it, use

$ sudo apt update
...
$ sudo apt install glances

Then run it using

$ glances