Linux Commands

Question 1

bash

Answer 1

Drops you to prompt
Let’s you know you’re in the bash shell
Ubuntu runs this
(mint too since it’s a variation on Ubuntu)

Question 2

echo $SHELL

Answer 2

Shows which shell you are in by folder

$SHELL = Variable that’s stored in the shell

Question 3

csh

Answer 3

C shell

Based around C programming language

Question 4

tshell

Answer 4

Variation on the csh (cshell)

Question 5

Why in a terminal do you see directory structure?

Answer 5

Linux treats everything as a file. So the folder structure is used to organize everything.

Question 6

For shells, what does CLI stand for?

Answer 6

Command line interpreter

The shell interprets commands as instructions to give the computer

Question 7

What’s the difference between internal commands and external commands?

Answer 7

Internal commands are anything the shell does by default. Or built into the shell.

External commands are commands that call to a third party program or runs through the shell out to a third party program.

Question 8

ls -l

ls -f | more

ls -lah

Answer 8

LS lists the files and folders in the working directory

ls -L gives the long output. Displays file details user and group that owns them including read write permissions.

-F shows folders from files because a file doesn’t need an extension in Linux

• a show all including hidden
• h human readable, files sizes as MB etc.
• la long and show all

You can also use MAN to learn about sorting by size, etc.

MORE displays one screen at a time

Question 9

pwd

Answer 9

Print working directory

Shows which folder you’re in currently.

Question 10

Username@domain: ~

^^ this is the command prompt, what does the ~ mean?

Answer 10

It means we are in the home directory for that user
Example
/home/Username
Normally that would be the current working directory

Question 11

cd 
cd by itself 
cd /
cd /folder/folder
cd ..

Answer 11

Change directory.
Same as windows

Cd by itself goes to home folder

cd / takes you to root

cd /directory/folder takes you directly to that directory (from the root of the folder structure)

cd .. takes you up one folder in the directory structure

Question 12

What’s the difference between exit and logout?

Answer 12

When in a GUI, exit will log you out and close the terminal window.

When you are in a LOGON SHELL, where all you see is the command line, Logout logs you out. Doesn’t shut down system or anything else etc.

Question 13

What are the ways you can pull CLI commands from a command prompt?

Can you run these commands again?

Answer 13

Up and down arrows to select previous commands, but when SSH’d in you may not be able to use arrow keys.

history command shows the last 500 commands
Use !501 to run the 501st command
Use !! To run the last command. Helpful when remoting in.
These are stored in a text document locally.
~/.bash_history

Question 14

What does .sh_history keep a record of?

Answer 14

Each shell maintains its own history separate from one another.

Question 15

At the prompt with a long string,
How can you move forward and backward through the arguments?

How do you move to the front or the back of the string?

Answer 15

Esc+F or B = jump forward or backward through the arguments

Ctrl+a or e = Jump to the front or the end of the string (like the tv show)

Helpful for when connecting remotely to a server or in a VM because arrow keys will not work.

Question 16

How do you create variables?

When interacting with variables on Linux, how do you set a variable?

And how do you print (display) a variable’s current value?

Answer 16

Example to set prompt name
PS1=“My Prompt:”

set $PS1
Sets variable values

unset $PS1
Removes All values from variable

echo $PS1
Prints variable value
You need the $ to call on variables

These variables are temporary unless added to the shell’s config profile
Bash RC or .profile, etc.

Question 17

What command shows all variables?

Answer 17

env

Environmental command shows a list of all the system variables that are set

Question 18

Which command helps you find information on a specific command?

Which command is used to find a command if you don’t recall the name?

Answer 18

Man [command]
Manual

2 options:
Most Linux distros use a whatis database command that’s a list of all commands and functions/descriptions on that distribution.

Finds a command based on what it does

apropos [keyword]
whatis [keyword]

Question 19

sudo

Answer 19

Runs command as Super user

Question 20

yum

Answer 20

Installs software and packages

Question 21

What does naming a file starting with a “.” do?

Answer 21

This hides the file by default

Question 22

File names in Linux maintain posix compliance. Give an example of one of the file name requirements.

Answer 22

Case sensitive unlike windows

Looks like Filenames can be set by the OS
Linux can have filenames up to 255 characters long, not counting the path.

Question 23

mv

mv * ../test

Answer 23

Rename or Move files or directories

Moves all files to a folder found in the parent directory (back one level) called test

Question 24

cp
cp * ./test
cp -R * ./test

Answer 24

Copies files or directories

cp * ./test
Copies all files to folder test, found in PWD

cp -R * ./test
Copy all folders and files to folder test, found in PWD.

Question 25

mkdir

Answer 25

Make directories

Question 26

rm
rm -r
rm -rf

Answer 26

Remove directory / delete

rm -r
Removes folders and files (recursive)

rm -rf
Forces the removal of they are protected.

Question 27

who

Answer 27

Shows who is logged in

Question 28

clear

Answer 28

Clears the terminal window

Question 29

systemctl

Answer 29

(Start / stop / enable / disable) manages OS services and start-ups

Question 30

firewalld-cmd

Answer 30

CentOS FW

Question 31

nano

Answer 31

Text editor

Not installed with minimum install

Question 32

touch [name]

Answer 32

Creates an empty file by a name you specified