A few simple commands

Congratulations on learning your first Linux command (date). Now let's keep learning more!

One would usually display the calendar after displaying that date, right? To display the calendar of the current month, you can run the cal command:

Figure 18 : The cal command

You can also display the calendar of the whole year, for example, to get the full 2022 calendar, you can run:

Figure 19: The cal command for the year 2022

You can also specify a month, for example, to display the calendar of February 1993, you can run the command:

Figure 20: The cal command for February 1993

You now have a lot of output on your Terminal. You can run the clear command to clear the Terminal screen:

Figure 21: Before clear

This is how your Terminal will look after running the clear command:

Figure 22: After clear

You can use the lscpu command, which is short for List CPU, to display your CPU architecture information:

elliot?ubuntu-linux:-$ lscpu 
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit 
Byte Order:            Little Endian
CPU(s):                1
On-line CPU(s) list:   0
Thread(s) per core:    1 
Core(s) per socket:    1 
Socket(s):             1
NUMA node(s):          1
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 61
Model name:            Intel(R) Core(TM) i5-5300U CPU? 2.30GHz Stepping: 4
CPU MHz:               2294.678
BogoMIPS:              4589.35
Hypervisor vendor:     KVM 
Virtualization type:   full 
Lid cache:             32K
L1i cache:             32K
L2 cache:              256K
L3 cache:              3072K 
NUMA nodeO CPU(s):     0
Flags:                 fpu vme de pse tsc msr pae mce cx8 apic sep mtrr

You can use the uptime command to check how long your system has been running. The uptime command also displays:

• The current time.
• The number of users that are currently logged on.
• The system load averages for the past 1, 5, and 15 minutes.

elliot?ubuntu-linux:-$ uptime
18:48:04 up 4 days, 4:02, 1 user, load average: 0.98, 2.12, 3.43

You might be intimidated by the output of the uptime command, but don't worry, the following table breaks down the output for you.

Table 1: uptime command output

You probably haven't heard about load averages before. To understand load aver-ages, you first have to understand system load.

WHAT IS SYSTEM LOAD?

In simple terms, system load is the amount of work the CPU per-forms at a given time.

So the more processes (or programs) running on your computer, the higher your system load is, and fewer processes running leads to a lower system load. Now, since you understand what a system load is, it's easy to understand load averages.

WHAT IS LOAD AVERAGE?

The load average is the average system load calculated over a given period of 1, 5, and 15 minutes.

So the three numbers that you see at the very end of the uptime command output are the load averages over 1, 5, and 15 minutes respectively. For example, if your load averages values are:

load average: 2.00, 4.00, 6.00

Then these three numbers represent the following:

• 2.00 --+: The load average over the last minute.
• 4.00 --+: The load average over the last five minutes.
• 6.00 --+: The load average over the last fifteen minutes.

From the definition of load average, we can conclude the following key points:

1. A load average of value 0.0 means the system is idle (doing nothing).
2. If the 1-minute load average is higher than the 5- or 15-minute averages, then this means your system load is increasing.
3. If the 1-minute load average is lower than the 5- or 15-minute averages, then this means your system load is decreasing.

For instance, load averages of:

load average: 1.00, 3.00, 7.00

Shows that the system load is decreasing over time. On the other hand, load averages of:

load average: 5.00, 3.00, 2.00

Indicates that the system load is increasing over time. As an experiment, first take note of your load averages by running the uptime command, then open up your web browser and open multiple tabs, then rerun up-time; you will see that your load averages have increased. After that, close your browser and run uptime again, you will see your load averages have decreased.

You can run the reboot command to restart your system:

elliot?ubuntu-linux:-$ reboot

You can run the pwd command to print the name of your current working directory:

elliot?ubuntu-linux:-$ pwd
/home/elliot

The current working directory is the directory in which a user is working at a given time. By default, when you log into your Linux system, your current working directory is set to your home directory:

/home/your_username

WHAT IS A DIRECTORY?

In Linux, we refer to folders as directories. A directory is a file that contains other files.

You can run the ls command to list the contents of your current working directory:

elliot?ubuntu-linux:-$ ls
Desktop Documents Downloads Music Pictures Public Videos

If you want to change your password, you can run the passwd command:

elliot?ubuntu-linux:-$ passwd 
Changing password for elliot. 
(current) UNIX password:
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully

You can use the hostname command to display your system's hostname:

elliot?ubuntu-linux:-$ hostname 
ubuntu-linux

You can use the free command to display the amount of free and used memory on your system:

elliot?ubuntu-linux:-$ free
          total      used    free   shared   buff/cache  available 
Mem:    4039732   1838532  574864    71900      1626336    1848444
Swap:    969960         0  969960

By default, the free command displays the output in kilobytes, but only aliens will make sense out of this output.

You can get an output that makes sense to us humans by running the free command with the -h option:

elliot?ubuntu-linux:-$ free -h
         total     used     free     shared     buff/cache     available
Mem:      3.9G     1.8G     516M        67M           1.6G          1.7G
Swap:     947M       OB     947M 

That's much better, right? The -h is short for --human, and it displays the output in a human-readable format.

You may have noticed that this is the first time we ran a command with an option. The majority of Linux commands have options that you can use to change their default behavior slightly.

You should also know that command options are either preceded by a single hyphen (-) or a double hyphen (--). You can use a single hyphen if you are using the abbreviated name of the command option. On the other hand, if you are using the full name of the command option, then you need to use a double hyphen:

elliot?ubuntu-linux:-$ free --human
         total     used     free     shared     buff/cache     available
Mem:      3.9G     1.8G     516M        67M           1.6G          1.7G
Swap:     947M       OB     947M 

As you can see, the previous two runs of the free command yielded the same output. The only difference is that the first time, we used the abbreviated command option name -h, and so we used a single hyphen. In the second time, we used the full command option name --human, and so we used a double hyphen.

You have the freedom of choice when it comes to using the abbreviated command option names versus the full command option names.

You can use the df command to display the amount of disk space available on your system:

elliot?ubuntu-linux:-$ df
Filesystem     1K-blocks     Used     Available     Use%      Mounted on
udev             1989608        0       1989608       0%            /dev
tmpfs             403976     1564        402412       1%            /run
/dev/sda1       20509264  6998972      12445436      36%           /
tmpfs            2019864    53844       1966020       3%        /dev/shm
tmpfs               5120        4          5116       1%       /run/lock
tmpfs            2019864        0       2019864       0%  /sys/fs/cgroup
/dev/loop0         91648    91648             0     100% /snap/core/6130
tmpfs             403972       28        403944       1%   /run/user/121
tmpfs             403972       48        403924       1%  /run/user/1000

Again you may want to use the human-readable option -h to display a nicer format:

elliot?ubuntu-linux:-$ df -h
Filesystem       Size      Used      Avail     Use%      Mounted on
udev             1.9G         0       1.9G       0%            /dev
tmpfs            395M      1.6M       393M       1%            /run
/dev/sda1         20G      6.7G        12G      36%            /
tmpfs            2.0G       57M       1.9G       3%        /dev/shm
tmpfs            5.0M      4.0K       5.0M       1%       /run/lock
tmpfs            2.0G         0       2.0G       0%  /sys/fs/cgroup
/dev/loop0        90M       90M          0     100% /snap/core/6130
tmpfs            395M       28K       395M       1%   /run/user/121
tmpfs            395M       48K       395M       1%  /run/user/1000

Don't worry if you can't understand everything you see in the output, as I will ex-plain everything in detail in the following chapters. The whole idea of this chapter is to get your feet wet; we will pe deep later with the sharks!

The echo command is another very useful command; it allows you to print a line of text on your Terminal. For example, if you want to display the line Cats are better than Dogs! on your Terminal, then you can run:

elliot?ubuntu-linux:-$ echo Cats are better than Dogs! 
Cats are better than Dogs!

You might be asking yourself, "How on earth is this useful?" Well, I promise you that by the time you finish reading this book, you would have realized the immense benefits of the echo command.

You can spend a great amount of time on your Terminal, punching in commands. Sometimes, you may want to rerun a command, but you may have forgotten the name of the command or the options that you have used, or you are simply lazy and don't want to type it again. Whatever the case may be, the history command will not let you down.

Let's run the history command and see what we get here:

elliot?ubuntu-linux:-$ history
1 date
2 blabla
3 cal
4 cal 2022
5 cal feb 1993
6 clear
7 lscpu
8 uptime
9 reboot
10 pwd
11 ls
12 passwd
13 hostname
14 free
15 free -h
16 free --human
17 df
18 df -h
19 echo Cats are better than Dogs!
20 history

As expected, the history command displayed all the commands that we ran so far in chronological order. On my history list, the lscpu command is number 7, so If I want to rerun lspcu, all I need to do is run !7:

elliot?ubuntu-linux:-$ !7 
lscpu
Architecture:         x86_64
CPU op-mode(s):       32-bit, 64-bit
Byte Order:           Little Endian 
CPU(s):               1
On-line CPU(s) list:  0
Thread(s) per core:   1
Core(s) per socket:   1
Socket(s):            1
NUMA node(s):         1
Vendor ID:            GenuineIntel
CPU family:           6
Model:                61
Model name:           Intel(R) Core(TM) i5-5300U CPU @ 2.30GHz
Stepping:             4
CPU MHz:              2294.678
BogoMIPS:             4589.35
Hypervisor vendor:    KVM
Virtualization type:  full
Lid cache:            32K
L1i cache:            32K
12 cache:             256K
13 cache:             3072K 
NUMA node0 CPU(s):    0
Flags:                fpu vme de pse tsc msr pae mce cx8 apic sep mtrr

UP AND DOWN ARROW KEYS

You can scroll up and down on your command line history. Every time you hit your up arrow key, you scroll up one line in your command history.

You can also reverse and scroll down with your down arrow key.

You can use the uname command to display your system's kernel information. When you run the uname command without any options, then it will print just the kernel name:

elliot?ubuntu-linux:-$ uname 
Linux

You can use the -v option to print the current kernel version information:

elliot?ubuntu-linux:-$ uname -v
#33-Ubuntu SMP Wed Apr 29 14:32:27 UTC 2020

You can also use the -r option to print the current kernel release information:

elliot?ubuntu-linux:-$ uname -r 
5.4.0-29-generic

You can also use the -a option to print all the information of your current kernel at once:

elliot?ubuntu-linux:-$ uname -a
Linux ubuntu-linux 5.4.0-29-generic #33-Ubuntu SMP
Wed Apr 29 14:32:27 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

You can also run the lsb_release -a command to display the Ubuntu version you are currently running:

elliot?ubuntu-linux:-$ lsb_release -a 
No LSB modules are available.
Distributor ID: Ubuntu 
Description: Ubuntu 20.04 LTS 
Release: 20.04
Codename: focal

Finally, the last command you are going to learn in this chapter is the exit command, which terminates your current Terminal session:

elliot?ubuntu-linux:-$ exit

A COOL FACT

You may have already observed by now that Linux command names pretty much resemble what they do. For instance, the pwd command liter-ally stands for Print Working Directory, ls stands for List, lscpu stands for List CPU, etc. This fact makes it much easier remembering Linux commands.

Congratulations! You made it through the first chapter. Now it's time for your first knowledge check exercise.