lk/fundamentals/basics.md

Absolute Bloody Basics

You need about a dozen commands to move around Linux. After that, you look up the rest as you go. Don't worry about understanding any of it, just type it in and the habit forms pretty quickly.

You start in a dark room. You have a 'look-see' what's in front of you:

ls

If you get no response, the list of items is "", meaning "nothing here".

Have a look at all the files:

ls -a

. ..

So . means 'here' and .. means 'you see stairs leading downwards'.

Find out where you are by printing out your current 'directory' (i.e. 'location'):

pwd

Change directory (cd) down one level:

cd ..

Look where you are again with pwd, then go back up. Use ls, and if you see bob, then:

cd bob

Move around the directories. The place at the bottom is the 'root', and is known as /. Go to the root:

cd /

Do ls again and change into etc. Look at how much space those folders are taking up:

du iptables

That's the number of kilobytes the file is taking up. Do the same again, but in a human-readable format:

du -h iptables

The du program has -h for 'human', '-s' for 'short', and a bunch of other commands. Have a look at the manual and try another command:

man du

Once you're done, press 'q' to quit the manual page and try the extra du flag you've found.

Now you can try to gain super-powers and take over the system:

sudo -i

At this point, you are 'root'. All your commands will be executed, even if they're unsafe, or even if you ask to delete the entire machine. Best to exit out of the root account:

exit

Go find a file that isn't a directory. You can tell which is which with:

ls -l

A directory starts with a 'd', like this:

drwxr-xr-x 79 root root 4096 Jan 3 05:15 /etc/

A standard file starts with '-', like this:

-rw-r--r-- 1 root root 8 Dec 11 17:26 hostname

Look inside the file /etc/hostname to find out your computer's name:

cat /etc/hostname

Print out the words "hello world":

echo "hello world"

Move back to your home directory:

cd

Take the words 'hello world', and put them in 'my_file':

echo 'hello world' > my_file

Measure the disk usage of that file, then put the results at the bottom of the file:

du my_file >> my_file

And check the results:

cat my_file

Autocompletion

Press tab after a few keys and bash will guess what you're trying to type.

Permissions

Look at your file's owner:

ls -l my_file

If it says -rw-r--r-- 1 root root 8 Dec 11 17:26 hostname then the file is owned by 'root'.

Take your file and change the owner to root:

sudo chown root my_file

Change the same file so it's owned by the group 'audio':

sudo chown :audio my_file

Check you did that correctly:

ls -l my_file

-rw-r--r-- 1 root audio 0 Jan 3 19:20 my_file

Read the start of that line. Root can 'read' and 'write' to or delete the file. Try to remove (delete) it:

rm my_file

You'll see you're not allowed, because you don't own it.

Look at which groups you're in:

groups

Change the file so that members of the audio group can write to the file:

sudo chmod g+w my_file

Check you got it right with ls -l:

-rw-rw-r-- 1 root audio 0 Jan 3 19:20 my_file

Try to delete the file again:

rm my_file

If you can't, you're not in the audio group. Add yourself. You'll need to modify your user account, by appending 'audio' to your list of groups. Use -a to append, and -G, to say you're modifying groups:

sudo usermod -a -G audio [ your username here ]

Now you should be able to remove (delete) the file. Remember, that using 'rm file' will not send it to a recycling bin. The file is gone.

Directories

Make a directory called 'new test':

mkdir 'new test'

Make two directories, called 'A', and 'Z':

mkdir A Z

Text Searches

Measure the disk usage of everything ('*' means 'everything'), and put it in a file called 'disk usage.txt':

du -sch * > A/'disk usage'.txt

Look at your file:

cat A/'disk usage.txt'

If you think you have too much information, use grep to just get the one line of text you want:

grep total A/disk\ usage.txt

The grep program also has a manual ('man page'). You should find out what that -c flag does, but the manual is too long to read.

Start the manual:

man du

Then search for -c by pressing /. Your final keys should be man du, then /-c

Find out if the ls program also has a 'human readable' format by using grep to search for the word 'human':

man ls | grep human

Now use that flag that you've found in combinatin with the -l flag to look at a file.

Remove the directory 'Z':

rmdir Z

Remove the directory 'Z':

rmdir Z

And then remove all the rest:

rmdir *

The 'A' directory will not budge as it's not empty. Remove it recursively, so the computer will remove the things inside the directory as well as the directory itself:

rm -r A

Installation

You get a package mangaer which installs programs, fonts, et c. If you're on something like Debian, you'll have apt, or if you're on something like Red Hat, you'll have yum. If unsure, ask where a program is:

whereis yum

whereis apt

If you get a hit, you can use whatever program that is to install things.

Set a reminder of your package manager:

echo my package manager is yum | lolcat

That failed because you don't have lolcat installed. Install lolcat:

sudo apt install lolcat

Try the same command again.

Search for things you want, like libreoffice, or gimp:

apt search libreoffice

... then install one of them with:

apt install [ thing ]

Remove lolcat, because it's useless:

sudo apt remove lolcat

... and that's pretty much it. You can move, create, destroy, install things, and look things up.

Review

• Search for random things with your package manager and install the interesting ones.
  • Read the manual with man thing
  • If it's useless, remember to uninstall it.
• Have a look around the file system in /.
• Look in the .config folder in your home directory.
  • If you copy a program's config to another machine, the program will behave just like you set it up in your own machine.