Getting Started with Linux Fundamentals

Linux runs virtual consoles to allow users independent login sessions. These virtual consoles are also referred to as TTY consoles. The first TTY runs the GNOME Desktop Manager (GDM) service, in which you log in to the system. When you log in to the GNOME desktop, your session occupies the second TTY automatically.

Even with a graphical environment enabled, you can log in to your local machine by using a text-only console. To use a text-only console, switch to an unused TTY. For example, press Alt+Ctrl+F3 to switch to the third virtual console.

Unlike a desktop session, a console session does not lock itself after an inactivity period, so make sure to close the session after you finish your work. You can close the session by typing exit or by pressing Ctrl+d.

To return to the desktop session, press Alt+Ctrl+F2. Or you can press Alt+Ctrl+F1 to return to the GDM.

In Linux, you commonly run commands to interact with the computer. By running commands, you can avoid navigating through different tools to obtain system information or to perform a simple task. For example, to view the computer name, you can open the settings application, navigate to the About section, and review the Device Name label. Alternatively, in a terminal, you use only the hostname command.

In the following example, the command returns mycomputer.example.com, which is the full name of the machine.

[user@host ~]$ hostname
mycomputer.example.com

Most commands have a default action when they are run, but the command is not limited to performing that action. You can add one or more options to a command to modify its behavior. Generally, a command option starts with a dash (-) and uses a single letter, or the option starts with two dashes (--) and uses a word.

In the following examples, you add the -d option to show the domain name and the -s option to show the short name of the machine.

[user@host ~]$ hostname -d
example.com
[user@host ~]$ hostname -s
mycomputer

A command also accepts arguments. Arguments are the target of the command, such as a file or other object upon which the command acts.

For example, the id command prints the user ID that the system uses to uniquely identify a user. In the following example, you use the id command by itself. Because you do not use options, the id command performs its default action, which is to print the current user information.

[user@host ~]$ id
uid=1000(user) gid=1000(user) groups=1000(user),10(wheel)
...output omitted...

In the following example, you use the id command with an option, but with no argument. The -u option specifies to print only the user ID. The command assumes the current user as the argument.

[user@host ~]$ id -u
1000

In the final example, you use the id command with both an option and an argument. The id command receives devops as the target user for the command. The -u option prints the devops user ID, which is different from the previous example.

[user@host ~]$ id -u devops
1001

Commands can have multiple options and the meaning of the options are not interchangeable between commands. You can view the options for a command by using the --help option.

The who command shows the users who are logged in to the machine.

[user@host ~]$ who --help
Usage: who [OPTION]... [ FILE | ARG1 ARG2 ]
Print information about users who are currently logged in.

  -a, --all         same as -b -d --login -p -r -t -T -u
  -b, --boot        time of last system boot
...output omitted...

The date and timedatectl commands provide time information. The main difference is that by default, the timedatectl command shows time zone information and whether the machine clock is synced with a time server. This sync information is important because some services rely on the system time to work correctly.

The following example shows the output of the date and timedatectl commands:

[student@workstation ~]$ date
Fri Sep 29 13:35:20 EDT 2023

[student@workstation ~]$ timedatectl
               Local time: Fri 2023-09-29 13:35:22 EDT
           Universal time: Fri 2023-09-29 17:35:22 UTC
                 RTC time: Fri 2023-09-29 17:35:22
                Time zone: America/New_York (EDT, -0400)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

The passwd command update user passwords. By default, it changes the current user's password, so you do not need to specify the account name as an argument. The root user, however, can change the password for any user. In this scenario, you must specify the target account as the argument.

With tab completion, you request that the shell program completes a command by pressing the Tab key. If you have typed enough characters that a command word is uniquely matched, then the shell completes the word. If the characters that you entered do not match a unique command, then the shell completes as many characters as it can, and then stops until you provide additional characters. Pressing Tab a second time displays the command words that match the typed pattern.

In the following example, typing host and pressing Tab twice displays four choices. When you type an additional n and press Tab again, the shell completes the hostname command.

[user@host ~]$ hostTab+Tab 
host         hostid       hostname     hostnamectl
[user@host ~]$ hostnTab 
[user@host ~]$ hostname
mycomputer.example.com