The Linux Operating System
An Operating System is the suite of programs that make a computer work. Like Microsoft and Apple MacOS, Linux is an operating system, and it is open source.
In general, the Linux operating system is made up of three parts; the kernel, the shell, and the programs.
The Kernel, the shell, and the programs
If we think of the Linux operating system in terms of layers, the kernel is the lowest layer. It interfaces directly with the computer hardware and is responsible for allocating and managing the resources available to programs. It allocates processor time and memory to each program and determines when each program will run. The kernel also provides an interface to programs, allowing them to access files, the network, and devices.
The shell is a computer program that uses a command-line interface (CLI) to pass commands made by your keyboard to your operating system. Most people are used to interacting with a graphic user interface (GUI), where you can use a combination of your mouse and keyboard to carry out commands on your computer. We can use the shell through a terminal program.
The Directory and Files' Structure
One of the main features of Linux is that it includes a variety of small programs to meet various needs. Typically, each of these programs does one thing and does it well. This modular design allows the functionality of small programs to be mixed and matched. As you become more familiar with Linux, you will find that this design provides you great flexibility and power to accomplish almost any task. Typically these programs operate on top of the shell, but they may also interface directly with the kernel.
The Directory Structure
All the files are grouped in the directory structure. The file system is arranged in a hierarchical structure, like an inverted tree. The top of the hierarchy is traditionally called root (written as a "/").
We can use the print working directory command to see what directory we are currently in.
pwd
The Linux Basic commands
Here are the Linux commands list and their functionality
You can always use man and --help commands to see usage and options of each command, for example
man pwd
(Hit q to exit out of man page)
pwd --help
pwd
Use the pwd command to find out the path of the current working directory (folder) you’re in. The command will return an absolute (full) path, which is basically a path of all the directories that starts with a forward slash (/). An example of an absolute path is /home/username.
cd
To navigate through the Linux files and directories, use the cd command. It requires either the full path or the name of the directory, depending on the current working directory that you’re in.
Let’s say you’re in /home/username/Documents and you want to go to Photos, a subdirectory of Documents. To do so, simply type the following command: cd Photos.
Another scenario is if you want to switch to a completely new directory, for example,/home/username/Movies. In this case, you have to type cd followed by the directory’s absolute path: cd /home/username/Movies.
There are some shortcuts to help you navigate quickly:
cd .. (with two dots) to move one directory up
cd to go straight to the home folder
cd- (with a hyphen) to move to your previous directory
On a side note, Linux’s shell is case sensitive. So, you have to type the name’s directory exactly as it is.
ls
The ls command is used to view the contents of a directory. By default, this command will display the contents of your current working directory.
If you want to see the content of other directories, type ls and then the directory’s path. For example, enter ls /home/username/Documents to view the content of Documents.
There are variations you can use with the ls command:
ls -R will list all the files in the sub-directories as well
ls -a will show the hidden files
ls -al will list the files and directories with detailed information like the permissions, size, owner, etc.
cat
cat (short for concatenate) is one of the most frequently used commands in Linux. It is used to list the contents of a file on the standard output (sdout). To run this command, type cat followed by the file’s name and its extension. For instance: cat file.txt.
Here are other ways to use the cat command:
cat > filename creates a new file
cat filename1 filename2>filename3 joins two files (1 and 2) and stores the output of them in a new file (3)
to convert a file to upper or lower case use, cat filename | tr a-z A-Z >output.txt
cp
Use the cp command to copy files from the current directory to a different directory. For instance, the command cp scenery.jpg /home/username/Pictures would create a copy of scenery.jpg (from your current directory) into the Pictures directory.
mv
The primary use of the mv command is to move files, although it can also be used to rename files.
The arguments in mv are similar to the cp command. You need to type mv, the file’s name, and the destination’s directory. For example: mv file.txt /home/username/Documents. To rename files, the Linux command is mv oldname.ext newname.ext
mkdir
Use mkdir command to make a new directory — if you type mkdir Music it will create a directory called Music.
There are extra mkdir commands as well:
To generate a new directory inside another directory, use this Linux basic command mkdir Music/Newfile
use the p (parents) option to create a directory in between two existing directories. For example, mkdir -p Music/2020/Newfile will create the new “2020” file.
rmdir
If you need to delete a directory, use the rmdir command. However, rmdir only allows you to delete empty directories.
rm
The rm command is used to delete directories and the contents within them. If you only want to delete the directory — as an alternative to rmdir — use rm -r. Note: Be very careful with this command and double-check which directory you are in. This will delete everything and there is no undo.
touch
The touch command allows you to create a blank new file through the Linux command line. As an example, enter touch /home/username/Documents/Web.html to create an HTML file entitled Web under the Documents directory.
locate
You can use this command to locate a file, just like the search command in Windows. What’s more, using the -i argument along with this command will make it case-insensitive, so you can search for a file even if you don’t remember its exact name.
To search for a file that contains two or more words, use an asterisk (*). For example, locate -i school*note command will search for any file that contains the word “school” and “note”, whether it is uppercase or lowercase.
find
Similar to the locate command, using find also searches for files and directories. The difference is, you use the find command to locate files within a given directory.
As an example, find /home/ -name notes.txt command will search for a file called notes.txt within the home directory and its subdirectories.
Other variations when using the find are:
To find files in the current directory use, find . -name notes.txt
To look for directories use, / -type d -name notes. txt
grep
Another basic Linux command that is undoubtedly helpful for everyday use is grep. It lets you search through all the text in a given file.
To illustrate, grep blue notepad.txt will search for the word blue in the notepad file. Lines that contain the searched word will be displayed fully.
df
Use df command to get a report on the system’s disk space usage, shown in percentage and KBs. If you want to see the report in megabytes, type df -m.
du
If you want to check how much space a file or a directory takes, the du (Disk Usage) command is the answer. However, the disk usage summary will show disk block numbers instead of the usual size format. If you want to see it in bytes, kilobytes, and megabytes, add the -h argument to the command line.
head
The head command is used to view the first lines of any text file. By default, it will show the first ten lines, but you can change this number to your liking. For example, if you only want to show the first five lines, type head -n 5 filename.ext.
tail
This one has a similar function to the head command, but instead of showing the first lines, the tail command will display the last ten lines of a text file. For example, tail -n filename.ext.
diff
Short for difference, the diff command compares the contents of two files line by line. After analyzing the files, it will output the lines that do not match. Programmers often use this command when they need to make program alterations instead of rewriting the entire source code.
The simplest form of this command is diff file1.ext file2.ext
tar
The tar command is the most used command to archive multiple files into a tarball — a common Linux file format that is similar to zip format, with compression being optional.
This command is quite complex with a long list of functions such as adding new files into an existing archive, listing the content of an archive, extracting the content from an archive, and many more. Check out some practical examples to know more about other functions.
chmod
chmod is another Linux command, used to change the read, write, and execute permissions of files and directories. As this command is rather complicated, you can read the full tutorial in order to execute it properly.
chown
In Linux, all files are owned by a specific user. The chown command enables you to change or transfer the ownership of a file to the specified username. For instance, chown linuxuser2 file.ext will make linuxuser2 as the owner of the file.ext.
jobs
jobs command will display all current jobs along with their statuses. A job is basically a process that is started by the shell.
kill
If you have an unresponsive program, you can terminate it manually by using the kill command. It will send a certain signal to the misbehaving app and instructs the app to terminate itself.
There is a total of sixty-four signals that you can use, but people usually only use two signals:
SIGTERM (15) — requests a program to stop running and gives it some time to save all of its progress. If you don’t specify the signal when entering the kill command, this signal will be used.
SIGKILL (9) — forces programs to stop immediately. Unsaved progress will be lost.
Besides knowing the signals, you also need to know the process identification number (PID) of the program you want to kill. If you don’t know the PID, simply run the command ps ux.
After knowing what signal you want to use and the PID of the program, enter the following syntax:
kill [signal option] PID.
ping
Use the ping command to check your connectivity status to a server. For example, by simply entering ping google.com, the command will check whether you’re able to connect to Google and also measure the response time.
wget
The Linux command line is super useful — you can even download files from the internet with the help of the wget command. To do so, simply type wget followed by the download link.
uname
The uname command, short for Unix Name, will print detailed information about your Linux system like the machine name, operating system, kernel, and so on.
top
As a terminal equivalent to Task Manager in Windows, the top command will display a list of running processes and how much CPU each process uses. It’s very useful to monitor system resource usage, especially knowing which process needs to be terminated because it consumes too many resources.
history
When you’ve been using Linux for a certain period of time, you’ll quickly notice that you can run hundreds of commands every day. As such, running history command is particularly useful if you want to review the commands you’ve entered before.
man
Confused about the function of certain Linux commands? Don’t worry, you can easily learn how to use them right from Linux’s shell by using the man command. For instance, entering man tail will show the manual instruction of the tail command.
echo
This command is used to move some data into a file. For example, if you want to add the text, “Hello, my name is John” into a file called name.txt, you would type echo Hello, my name is John >> name.txt
zip, unzip
Use the zip command to compress your files into a zip archive, and use the unzip command to extract the zipped files from a zip archive.
hostname
If you want to know the name of your host/network simply type hostname. Adding a -I to the end will display the IP address of your network.
useradd, userdel
Since Linux is a multi-user system, this means more than one person can interact with the same system at the same time. useradd is used to create a new user, while passwd is adding a password to that user’s account. To add a new person named John type, useradd John and then to add his password type, passwd 123456789.
To remove a user is very similar to adding a new user. To delete the users account type, userdel UserName
Bonus Tips and Tricks
Use the clear command to clean out the terminal if it is getting cluttered with too many past commands.
Try the TAB button to autofill what you are typing. For example, if you need to type Documents, begin to type a command (let’s go with cd Docu, then hit the TAB key) and the terminal will fill in the rest, showing you cd Documents.
Ctrl+C and Ctrl+Z are used to stop any command that is currently working. Ctrl+C will stop and terminate the command, while Ctrl+Z will simply pause the command.
If you accidental freeze your terminal by using Ctrl+S, simply undo this with the unfreeze Ctrl+Q.
Ctrl+A moves you to the beginning of the line while Ctrl+E moves you to the end.
You can run multiple commands in one single command by using the “;” to separate them. For example Command1; Command2; Command3. Or use && if you only want the next command to run when the first one is successful.
- How do I extract tar or tar.gz file and directory in Linux?
- Tar.gz or Tar archives, zips and compresses files and directories. In order to extract/untar a Tar file in linux, you can type in the following commands in command prompt:-
tar xzf file.tar.gz- to uncompress a gzip tar file (.tgz or .tar.gz)
tar xjf file.tar.bz2 - to uncompress a bzip2 tar file (.tbz or .tar.bz2) to extract the contents.
tar xf file.tar - to uncompressed tar file (.tar)
tar xC /var/tmp -f file.tar - to uncompress tar file (.tar) to another directory
Here are the explanations for the flags that has been used:-
x = extract, this indicated an extraction c = create to create
v = verbose (optional) the files with relative locations will be displayed.
z = gzip-ped; j = bzip2-zipped
f = from/to file ... (what is next after the f is the archive file)
C = directory. In c and r mode, this changes the directory before adding the following files. In x mode, changes directoriy after opening the archive but before extracting entries from the archive.
The files will be extracted in the current folder (most of the times in a folder with the name 'file-1.0'). - Linux Commands' Display Map
Click here to see a display map of some useful Linux commands >> https://www.xmind.net/m/WwtB/#
The Linux Text editors
There are different text editors available in Linux to leverage. The useful and popular ones are vi, nano, emacs
You can create, edit and manipulate files through these editors:
Vi
Vi is the default text editor in Linux. The UNIX vi editor is a full screen editor and has two modes of operation:
1 - Command mode commands which cause action to be taken on the file, and
2 - Insert mode in which entered text is inserted into the file.
In the command mode, every character typed is a command that does something to the text file being edited; a character typed in the command mode may even cause the vi editor to enter the insert mode. In the insert mode, every character typed is added to the text in the file; pressing the <Esc> (Escape) key turns off the Insert mode.
While there are a number of vi commands, just a handful of these is usually sufficient for beginning vi users. To assist such users, this Web page contains a sampling of basic vi commands. The most basic and useful commands are marked with an asterisk (* or star) in the tables below. With practice, these commands should become automatic.
NOTE: Both UNIX and vi are case-sensitive. Be sure not to use a capital letter in place of a lowercase letter; the results will not be what you expect.
Nano - GNU nano is a small and friendly text editor. Besides basic text editing, nano offers many extra features like an interactive search and replace, go to line and column number, auto-indentation, feature toggles, internationalization support, and filename tab completion.
https://www.nano-editor.org/dist/v2.2/nano.html
Emacs - Emacs is one of the oldest and most versatile text editors. The GNU Emacs version was originally written in 1984 and is well known for its powerful and rich editing features. To run it, type in:
$ emacs
Emacs has a GUI and is easy to open file and edit files with.
Cat - can be used to display the content of a file, copy content from one file to another, concatenate the contents of multiple files, display the line number, display $ at the end of the line, etc.
The cat command can be used for piping a file to any program that expects binary data or plain text on the input stream. The cat command doesn't damage non-text bytes when outputting and concatenating. As such, the two primary use cases of this command are certain format-compatible binary file types and text files.
cat > [fileName] To create a file.
cat [oldfile] > [newfile] To copy content from older to new file.
cat [file1 file2 and so on] > [new file name] To concatenate contents of multiple files into one.
cat -n/cat -b [fileName] To display line numbers.
cat -e [fileName] To display $ character at the end of each line.
cat [fileName] <<EOF Used as page end marker.
More - command is used to view the text files in the command prompt, displaying one screen at a time in case the file is large (For example log files). The more command also allows the user do scroll up and down through the page.
more [-options] [-num] [+/pattern] [+linenum] [file_name]
-d : Use this command in order to help the user to navigate. It displays “[Press space to continue, ‘q’ to quit.]” and displays “[Press ‘h’ for instructions.]” when wrong key is pressed.
-f : This option does not wrap the long lines and displays them as such.
-p : This option clears the screen and then displays the text.
-c : This command is used to display the pages on the same area by overlapping the previously displayed text.
-s : This option squeezes multiple blank lines into one single blank line.
-u : This option omits the underlines.