GNU/Linux Toolbox

The line of text after the prompt, which usually looks like this: username@hostname:~$, is stored in the buffer. Content of the buffer gets sent to the OS when you press Enter.

You can confirm with Enter from anywhere in the buffer, i.e. the blinking block doesn't have to be at the end of the line for this to work. There's a lot that you can do outside of just writing the text of a command with its options/flags and pressing Enter to confirm. Here's the list of such additional functionalities and means of editing content of the buffer:

Navigation

← and →
// moving the cursor one character at the time
Ctrl + ← and Ctrl + →
// moving the cursor one word at the time
Alt + B and Alt + F
// moving the cursor one word at the time
Backspace
// deleting back one character at the time
Alt + Backspace
// deleting back one word at the time
Delete
// deleting forward one character at the time
Alt + D
// deleting forward one word at the time
Ctrl + Delete
// deleting forward one word at the time
Ctrl + U
// deleting all characters from the cursor position until the beginning of the line
Ctrl + K
// deleting all characters from the cursor position until the end of the line
Ctrl + Y
// to yank (paste) the deleted (cut) text
Ctrl + W
// delete (cut) one word at the time, backwards
Alt + D
// delete (cut) one word at the time, forward
Ctrl + A
// changes cursor position to the beginning of the buffer
Home
// changes cursor position to the beginning of the buffer
Ctrl + E
// changes cursor position to the end of the buffer
End
// changes cursor position to the end of the buffer
Alt + .
// add (paste) an argument of the previous command

History

↑ and ↓
// browsing issued commands history back and forward
Ctrl + P and Ctrl + N
// browsing issued commands history back (Previous) and forward (Next)
Ctrl + R
// reverse-i-search feature, searching for a specific issued command
Ctrl + G
// to exit reverse-i-search gracefully

Auto-completion

Tab
// shell auto-completion feature (when one match is found)
2x Tab
// shell auto-completion feature (when multiple matches are found)

Assorted

Ctrl + Alt + T
// open new shell session
Ctrl + D
// close the current shell session
Ctrl + L
// clear the screen
clear
// clear the screen
sudo !!
// forgotten sudo in front of the previous command
Alt + C
// capitalize word
Alt + L
// lowercase word
\ + Enter
// next line of input

The simplest way to copy and paste within terminal emulator program is to paste the selected text with middle-click. If you you can't middle-click (in case you're using a trackball for instance) you can paste the contents of your clipboard with Ctrl+Shift+V. To copy text within terminal emulator use Ctrl+Shift+C.

Here document is an easy way of generating multi-line output in the terminal or creating text documents without an editor, which is fast and useful for training purposes. By using it you'll also learn a bit about input/output redirection, which is an extremely important element of Bash shell landscape and one of its key functionalities.

Example 1: Print using cat

$ cat << EOF
> This is my example text.
> It consists of:
> - multiple characters
> - multiple words
> - multiple lines of text
> EOF
This is my example text.
It consists of:
- multiple characters
- multiple words
- multiple lines of text

Example 2: Redirect and save to a file

$ cat << EOF > heredoc.txt
> This is my new example.
> This time these words will be sent/redirected to a file.
> My file is called heredoc.txt and I'll be able to display its contents with cat command.
> EOF
$ cat heredoc.txt
This is my new example.
This time these words will be sent/redirected to a file.
My file is called heredoc.txt and I'll be able to display its contents with cat command.


Nano is a basic Linux text editor and its behavior is very similar to Windows Notepad and MacOS TextEdit. It is installed by default on popular Linux distributions. The key strokes covering most common operations are listed comfortably in the box at the bottom of the screen. To learn more about it press Ctrl + G.

Vim is very versatile and feature-rich. It has a dozen editing modes, but I'll focus on two key ones: Insert mode (for editing text) and Normal mode (for editor commands). Vim does seem scary at first glance, but the feeling will subside, if you choose to get to know it better and practice using it. Learning the ins and outs of Vim can be a life-long adventure. Pursue of Vim excellence doesn't seem to end. There's always more to discover, but we're here to cover the basics.

Basic operations

 Insert mode

a // append text on the right to the current cursor position
A // append text at the end of the line
i // insert text on the left to the current cursor position
I // insert text at the beginning of the line
o // enter a new line below the current one
O // enter a new line above the current one

 Normal mode

x // delete the highlighted character
dd // delete the current line and place it in the buffer
yy // copy (yank) the current to the buffer
p // paste content of the buffer (below)
P // paste content of the buffer (above)
/phrase
// look for the phrase in the document (forward, N for next occurrence)
?phrase
// look for the phrase in the document (backward, N for next occurrence)
:$/old/new/g
// replace old string with new one in the current line (no confirmation)
:$/old/new/cg
// replace old string with new one in the current line (with confirmation)

 Saving and exiting

:w // save
:q // quit
:w! // force-save
:q! // force-quit

Navigation

h // move cursor left
j // move cursor down
k // move cursor up
l // move cursor right
w // move cursor to the beginning of the next word
b // move cursor to the beginning of the previous word
$ // move cursor to the end of the line
0 // move cursor to the beginning of the line
:$ // move cursor to the end of the file
:n // move cursor to the Nth line of the file
Ctrl + F // scroll one screenful down (forward)
Ctrl + B // scroll one screenful up (backward)
c // replace existing text
d // delete existing text
cw // replace existing text from the cursor postion until the end of word
dw // delete existing text from the cursor postion until the end of word
c$ // replace existing text from the cursor postion until the end of line
d$ // delete existing text from the cursor postion until the end of line

To practice your newly acquired Vim skills, go ahead and issue vimtutor command in your terminal.

man command displays system's manual of a specified program in the following format man program. It is called the system's manual pager, and this is an apt description, becasue it behaves like a pager (less), which I'll discuss in section 3.5. Thie most important sections of its output are DESCRIPTION, OVERVIEW, and OPTIONS, with an emphasis on the last one. Usually you'll go there to learn about program's flags that enable certain features. Flags alter its default behavior, for example with uname -a you get different result than with uname alone. Since man behaves like a pager it is searchable. To trigger search function you use forward slash /phrase. To scroll you can use scroll wheel (duh!). f/b or Page Up/Page Down or space allows to scroll one screenful at the time. To quit you press Q.

help is somewhat similar to man. It serves the same purpose. However it works only for shell built-in commands, like true, false, for, or if. Perhaps the first thing that you'll notice is its brevity. Also, most of the time it doesn't have sections like man. To list all shell built-ins just type help alone.

man man and help help were helpful in putting together the explanation above.

 3.1.1 whoami and hostname

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 3.1.2 su and sudo

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 3.2.1 pwd and cd

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 3.2.2 ls and tree

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 3.2.3 Wildcards and Tab autocompletion

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 3.2.4 find, xargs, and locate

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 3.3.1 Reverse-i-search and history

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 3.3.2 fc and hash

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 3.4.1 touch and rm

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 3.4.2 mkdir, rmdir and rm -r

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 3.4.3 Bash brace expansion

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 3.4.4 mv and rename

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 3.4.5 cp, ln and ln -s

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 3.4.6 basename, dirname, realpath, and readlink

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 3.5.1 echo and printf

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 3.5.2 cat, tac, and rev

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 3.5.3 nl, fold, and paste

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 3.5.4 wc, uniq and sort

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 3.5.5 less and most

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 3.5.6 head and tail

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 3.6.1 diff, comm, and cmp

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 3.6.2 tr, grep, sed, and awk

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 3.6.2 Introduction to regular expressions (regex)

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 3.7.1 tar

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 3.7.2 gzip and gunzip

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 3.7.3 bzip2 and bunzip2

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 3.7.4 xz and unxz

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 3.7.5 zip and unzip

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 3.7.6 rar and unrar

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 3.7.7 unar (The Unarchiver) + lsar

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 3.8.1 jobs, fg, and bg

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 3.8.2 sleep and watch

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 3.8.3 at, cron, and anacron

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 3.9.1 dpkg and apt

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 3.9.2 rpm and dnf

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Let's populate our system with characters from The Office series. We'll use adduser command, which is an interactive version of useradd. It doesn't require any flags to create a complete, fully-usable account. The actions below require superuser privileges, so my commands are prefixed with sudo.

For account creation I use sudo adduser username and for adding my newly created user to sudoers, those allowed to act as a superuser, sudo usermod -aG sudo username. I can then check if my user was successfully assigned to this group with groups username (doesn't require sudo).

After adding missing personnel and departments (with sudo addgroup groupname) this is what it looks like.

Now it's time to assign people to their respective roles. It can be done in bulk with a for loop (for i in user1 user2 user3; do usermod -aG groupname $i; done). For loops are outside the scope of this tutorial, but as you can see this use-case is rather self-explanatory. It's better to become root for this one (with sudo -i). We can see our recent changes with another simple loop (for i in mscott dschru jhalpe pbeesl ehanno rhowar amarti kmalon omarti; do groups $i; done). To get back to your user account just type exit.

Remember how Pam was transferred from Reception to Sales? We can do the same thing in the terminal with gpasswd and usermod. To make it more realistic we'll use Michael's account to perform the change.

Notice that sudo gpasswd -d user group has different order of arguments comparing to the usermod one.

Since Pam is married to Jim her status in our system has to reflect that. We can apply such change with usermod. Overwriting her username and Full Name can be achieved with sudo usermod -l new_user old_user and sudo usermod -c "New Name" new_user. When changing the username and Full Name, you also need to change user's home directory. This can be done with mv ../old_user ../new_user (to rename their directory in /home) and usermod -d /home/new_user new_user to apply the change to /etc/passwd. Now that we're done we can check if all went well with grep and find.

As you might have noticed I didn't change my user from Michael. For the sake of our scenario let's say that Michael became a chaplain and officiated their wedding.

If one of our employees is misbehaving we can suspend them by locking their account. Ryan, I'm really sorry. In passwd's command output "L" is for locked and "P" stands for unlocked.

passwd is commonly used to change your own or somebody else's password (with sudo). Practice it with passwd and sudo passwd user. It has more features, like deleting a password, forcing its expiration, locking/unlocking (as we've seen in section 4.1), or defining the time of its validity.

groupmod allows to change group's name. We're gonna illustrate it with the first thing that comes to mind after watching 93rd episode, Two Weeks.

deluser is self-explanatory. We use it to get rid of an account. Since Ryan was promoted to VP of Northeastern Sales and left the Scranton branch his account has to go.

If you don't have perl installed deluser will greet you with /usr/sbin/deluser: In order to use the --remove-home, --remove-all-files, and --backup features, you need to install the `perl' package. To accomplish that, run apt-get install perl.

Then you simply do as instructed, sudo apt update and sudo apt install perl -y.

delgroup does exactly what its name suggests. Ryan is no longer in Scranton, so our temp group can be deleted.

This concludes User and group management tutorial with The Office US. I hope you've enjoyed it.

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 6.1.1 users, who, w, and last

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 6.1.2 id and finger

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 6.2.1 type and whatis

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 6.2.2 which and whereis

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 6.2.3 file and stat

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 6.3.1 df, du, and ncdu

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 6.3.2 fdisk -l and mount

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 6.4.1 uptime, ps and top

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 6.4.2 kill, killall, nice, and renice

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 6.4.3 pgrep, pkill, and ps --pid

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 6.4.4 htop and glances

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 6.4.5 lscpu, free, and lshw

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The startup sequence consists of 5 high-level stages: UEFI/BIOS, MBR, GRUB 2, Kernel, and SystemD.

UEFI (Unified Extensible Firmware Interface) or BIOS (Basic Input/Output System) performs system's hardware check, POST (Power On Self Test). Its task is to ensure that your hardware works correctly. If it succeeds our next stop is MBR (Master Boot Record).

MBR is a place where information about GRUB 2 (GRand Unified Bootloader) is stored. It's located in the first sector of the bootable disk.

GRUB 2 tells the computer where to find system's kernel and loads it into memory. As a side note: It does that after its splash screen, which awaits user's action for a few seconds. It defaults to the kernel image specified in GRUB's configuration file.

Kernel is often called the core of an operating system. It basically controls everything that it does. Its task in boot process is to first extract itself (it is in compressed format to save space) and load sytemd.

SystemD initializes the user space and manages system services during the boot sequence. It's able to start multiple processes in parallel, which improves boot time. It mounts the filesystems defined in /etc/fstab file. In its configuration file there's an information on which target should be used for your session. For a desktop system it's target 5 by default. You can check it with runlevel or who -r command.

SystemD provides service manager that runs as PID 1 and starts the rest of the system. You can check your PID 1 process with htop --sort-key PID command. More information on htop can be found in section 6.4.

? (question mark)
represents any single character

* (asterisk)
represents zero or more characters

[ ] (square brackets)
specifies a range

{ } (curly brackets)
terms are separated by commas and each term must be the name of something or a wildcard. Example: cp {*.doc,*.pdf} ~

[!] and [^]
similar to the [ ] construct, except rather than matching any characters inside the brackets, it'll match any character, as long as it is not listed between the [ and ]; logical NOT

\ (backslash)
"escape" character, protects subsequent special character

. (dot)
matches any single character, equivalent to ? wildcard

\ (backslash)
"escape" character, protects subsequent special character

.* (dot and asterisk)
matches any string, equivalent to * wildcard

* (asterisk)
the proceeding item is to be matched zero or more times

^ (caret)
means "the beginning of the line"

$ (dollar sign)
means "the end of the line"

[ ] (square brackets)
specifies a range

|
logical OR relationship between wildcards

[^]
equivalent of [!] wildcard; logical NOT

[:upper:] uppercase letters
[:lower:] lowercase letters
[:alpha:] alphabetic (letters); [:upper] and [:lower:]
[:digit:] numbers in decimal (0 to 9)
[:alnum:] alphanumeric; [:alpha:] and [:digit:]
[:space:] whitespace (spaces, tabs, newlines and similar)
[:graph:] graphically printable characters excluding space
[:print:] printable characters including space
[:punct:] punctuation characters; [:graph:] minus [:alpha:] and [:digit:]
[:cntrl:] control characters; non-printable characters
[:xdigit:] characters that are hexadecimal digits