introduction to linux

After some teacher sponsor troubles, we finally got a meeting together last week, and we talked about Linux fundamentals.

The lecture can be accessed here.

I made a bunch of tasks for people to familiarize themselves with Linux. For each, I’ll explain the command I had in mind to achieve the result and what it does.

tasks

Create your shell server account

We used the webshell to access the shared blairsec server without MCPS blocking us. If you want to make an account, contact one of the captains over something like Discord for the security key.

View your current username

whoami. Just in the command.

View your current directory (should be something like /home/)

pwd. Again, just in the command.

Create two directories with a single command

mkdir directory1 directory2. The mkdir command accepts multiple directory names.

List the directories and files of your home directory

ls. Just in the command. If you want to be fancy, ls -a shows the hidden files and directories too.

Delete the first folder without using rm (there’s a very similar command)

rmdir directory1. Though it might not be really useful, rmdir removes directories that are empty.

Create an empty file in the second folder

cd directory2; touch file1.txt. First we change directory to directory2, and then touch command creates an empty file.

You could also just use touch directory2/file1.txt

Change to the home directory

cd ~. The ~ means the home directory for the current user.

List all files in the new folder while you are in the home directory

ls directory2. The ls command can take optional arguments which are the names of the directories or files you want to ls.

Write the current time into the empty file without looking at a clock (commands only)

date > file1.txt. The date command returns a string containing date and time information, and the > file1.txt writes the output into file1.txt.

Make a copy of the file and keep it in the same directory

cp file1.txt file2.txt. When we cp with two arguments which are just two filenames, it creates a new file from the second name and copies the contents of the first into the second.

Write the contents of your home directory into the original file (overwriting)

ls ~ > file1.txt. ls ~ lists the contents of the home directory, and > file1.txt writes the output into file1.txt.

Write the contents of your home directory into the copied file (no overwriting)

ls ~ >> file2.txt. ls ~ lists the contents of the home directory, and >> file1.txt writes the output into file2.txt.

Make a copy of the folder you created

cp -r directory2 directory3. cp -r recursively copies files from one directory to another. Note that directory3 doesn’t exist, so it is created and just the files are put into the new directory:

.
├── directory2
│   ├── file1.txt
│   └── file2.txt
└── directory3
    ├── file1.txt
    └── file2.txt

If directory3 already existed, then it would copy directory2 itself into directory3:

.
├── directory2
│   ├── file1.txt
│   └── file2.txt
└── directory3
    └── directory2
        ├── file1.txt
        └── file2.txt

Delete the original folder

rm -r directory2. The rm command deletes stuff, and -r is the recursive flag so directories will be deleted. You could also use -rf like me if you don’t want deletion confirmation in certain situations.

List the permissions of the copied folder and every file inside of it

ls -l directory3. The -l command flag means to use “long listing format”, which gives more details including file permissions.

Make the second file un-writable for the current user

chmod u-w directory3/file2.txt. chmod modifies file permissions. u refers to the file’s owner (user) which is us (in contrast to g which refers to the file’s group, or o which refers to other people).

Try to write to the second file and see it fail (permission denied)

To test this, I used echo 1 > directory3/file2.txt. echo 1 prints out a 1 and > tries to write that into directory3/file2.txt. However, we get back bash: directory2/file2.txt: Permission denied, which means our permission setting worked and we cannot write to the file.

Get an ASCII locomotive to run across your screen (try making it fly too)

sl command. It was specifically created to annoy people who frequently typo ls. To make it fly, use -F. There are a bunch of other cool options in the man(ual) page for it - man sl to view it.

See you at the next meeting, whenever that is!

~ josh