Linux Notes for Professionals

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30

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31

Chapter 10: Managing Services

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Section 10.1: Diagnosing a problem with a service

Section 10.2: Starting and Stopping Services

Section 10.3: Getting the status of a service

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Chapter 11: Modifying Users

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Section 11.1: Setting your own password

Section 11.2: Setting another user's password

Section 11.3: Adding a user

Section 11.4: Removing a user

Section 11.5: Removing a user and its home folder

Section 11.6: Listing groups the current user is in

Section 11.7: Listing groups a user is in

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Chapter 12: LAMP Stack

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Section 12.1: Installing LAMP on Arch Linux

Section 12.2: Installing LAMP on Ubuntu

Section 12.3: Installing LAMP stack on CentoOS

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Chapter 13: tee command

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Section 13.1: Write output to stdout, and also to a file

Section 13.2: Write output from the middle of a pipe chain to a file and pass it back to the pipe

Section 13.3: write the output to multiple files

Section 13.4: Instruct tee command to append to the file

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Chapter 14: Secure Shell (SSH)

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Section 14.1: Connecting to a remote server

Section 14.2: Installing OpenSSH suite

Section 14.3: Configuring an SSH server to accept connections

Section 14.4: Passwordless connection (using a key pair)

Section 14.5: Generate public and private key

Section 14.6: Disable ssh service

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Chapter 15: SCP

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Section 15.1: Secure Copy

Section 15.2: Basic Usage

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Chapter 16: GnuPG (GPG)

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Section 16.1: Exporting your public key

Section 16.2: Create and use a GnuPG key quickly

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Chapter 17: Network Configuration

Section 17.1: Local DNS resolution

Section 17.2: Configure DNS servers for domain name resolution

Section 17.3: See and manipulate routes

Section 17.4: Configure a hostname for some other system on your network

Section 17.5: Interface details

Section 17.6: Adding IP to an interface

Chapter 18: Midnight Commander

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Section 18.1: Midnight Commander function keys in browsing mode

Section 18.2: Midnight Commander function keys in file editing mode

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Chapter 19: Change root (chroot)

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Section 19.1: Requirements

Section 19.2: Manually changing root in a directory

Section 19.3: Reasons to use chroot

Chapter 20: Package Managers

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Section 20.1: How to update packages with the apt package manager

Section 20.2: How to install a package with the pacman package manager

Section 20.3: How to update packages with the pacman package manager

Section 20.4: How to update packages with yum

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Chapter 21: Compiling the Linux kernel

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Section 21.1: Compilation of Linux Kernel on Ubuntu

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Credits

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You may also like

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61

About

Please feel free to share this PDF with anyone for free,

latest version of this book can be downloaded from:

https://goalkicker.com/LinuxBook

This Linux® Notes for Professionals book is compiled from Stack Overflow

Documentation, the content is written by the beautiful people at Stack Overflow.

Text content is released under Creative Commons BY-SA, see credits at the end

of this book whom contributed to the various chapters. Images may be copyright

of their respective owners unless otherwise specified

This is an unofficial free book created for educational purposes and is not

affiliated with official Linux® group(s) or company(s) nor Stack Overflow. All

trademarks and registered trademarks are the property of their respective

company owners

The information presented in this book is not guaranteed to be correct nor

accurate, use at your own risk

Please send feedback and corrections to [email protected]

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1

Chapter 1: Getting started with GNU/Linux

Section 1.1: Useful shortcuts

Using The Terminal

The examples in this document assume that you are using a POSIX-compliant (such as bash, sh, zsh, ksh)

shell.

Large portions of GNU/Linux functionality are achieved using the terminal. Most distributions of Linux include

terminal emulators that allow users to interact with a shell from their desktop environment. A shell is a command-

line interpreter that executes user inputted commands. Bash (Bourne Again SHell) is a common default shell

among many Linux distributions and is the default shell for macOS.

These shortcuts will work if you are using Bash with the emacs keybindings (set by default):

Open terminal

Ctrl + Alt + T or Super + T

Cursor movement

Ctrl + A Go to the beginning of the line you are currently typing on.

Ctrl + E Go to the end of the line you are currently typing on.

Ctrl + XX Move between the beginning of the line and the current position of the cursor.

Alt + F Move cursor forward one word on the current line.

Alt + B Move cursor backward one word on the current line.

Ctrl + F Move cursor forward one character on the current line.

Ctrl + B Move cursor backward one character on the current line.

Text manipulation

Ctrl + U Cut the line from the current position to the beginning of the line, adding it to the clipboard. If

you are at the end of the line, cut the entire line.

Ctrl + K Cut the line from the current position to the end of the line, adding it to the clipboard. If you

are at the beginning of the line, cut the entire line.

Ctrl + W Delete the word before the cursor, adding it to the clipboard.

Ctrl + Y Paste the last thing from the clipboard that you cut recently (undo the last delete at the

current cursor position).

Alt + T Swap the last two words before the cursor.

Alt + L Make lowercase from cursor to end of word.

Alt + U Make uppercase from cursor to end of word.

Alt + C Capitalize to end of word starting at cursor (whole word if cursor is at the beginning of word).

Alt + D Delete to end of word starting at cursor (whole word if cursor is at the beginning of word).

Alt + . Prints the last word written in previous command.

Ctrl + T Swap the last two characters before the cursor.

History access

Ctrl + R Lets you search through previously used commands.

Ctrl + G Leave history searching mode without running a command.

Ctrl + J Lets you copy current matched command to command line without running it, allowing you to

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make modifications before running the command.

Alt + R Revert any changes to a command you’ve pulled from your history, if you’ve edited it.

Ctrl + P Shows last executed command, i.e. walk back through the command history (Similar to up

arrow).

Ctrl + N Shows next executed command, i.e. walk forward through the command history (Similar to

down arrow).

Terminal control

Ctrl + L Clears the screen, similar to the clear command.

Ctrl + S Stop all output to the screen. This is useful when running commands with lots of long output.

But this doesn't stop the running command.

Ctrl + Q Resume output to the screen after stopping it with Ctrl+S.

Ctrl + C End currently running process and return the prompt.

Ctrl + D Log out of the current shell session, similar to the exit or logout command. In some commands,

acts as End of File signal to indicate that a file end has been reached.

Ctrl + Z Suspends (pause) currently running foreground process, which returns shell prompt. You can

then use bg command allowing that process to run in the background. To again bring that process to

foreground, use fg command. To view all background processes, use jobs command.

Tab Auto-complete files and directory names.

Tab Tab Shows all possibilities, when typed characters doesn't uniquely match to a file or directory

name.

Special characters

Ctrl + H Same as Backspace.

Ctrl + J Same as Return (historically Line Feed).

Ctrl + M Same as Return (historically Carriage Return).

Ctrl + I Same as Tab.

Ctrl + G Bell Character.

Ctrl + @ Null Character.

Esc Deadkey equivalent to the Alt modifier.

Close Terminal

Ctrl + Shift + W To close terminal tab.

Ctrl + Shift + Q To close entire terminal.

Alternatively, you can switch to the vi keybindings in bash using set -o vi. Use set -o emacs to switch back to the

emacs keybindings.

Section 1.2: File Management Commands

Linux uses some conventions for present and parent directories. This can be a little confusing for beginners.

Whenever you are in a terminal in Linux, you will be in what is called the current working directory. Often your

command prompt will display either the full working directory, or just the last part of that directory. Your prompt

could look like one of the following:

user@host ~/somedir $

user@host somedir $

user@host /home/user/somedir $

which says that your current working directory is /home/user/somedir.

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In Linux .. represents the parent directory and . represents the current directory.

Therefore, if the current directory is /home/user/somedir, then cd ../somedir will not change the working

directory.

The table below lists some of the most used file management commands

Directory navigation

Command

Utility

pwd

cd -

Get the full path of the current working directory.

Navigate to the last directory you were working in.

cd ~ or just cd Navigate to the current user's home directory.

cd ..

Go to the parent directory of current directory (mind the space between cd and ..)

Listing files inside a directory

Command

ls -l

Utility

List the files and directories in the current directory in long (table) format (It is recommended to

use -l with ls for better readability).

ls -ld dir-name List information about the directory dir-name instead of its contents.

ls -a

ls -F

ls -lt

ls -lh

ls -lR

tree

List all the files including the hidden ones (File names starting with a . are hidden files in Linux).

Appends a symbol at the end of a file name to indicate its type (* means executable, / means

directory, @ means symbolic link, = means socket, | means named pipe, > means door).

List the files sorted by last modified time with most recently modified files showing at the top

(remember -l option provides the long format which has better readability).

List the file sizes in human readable format.

Shows all subdirectories recursively.

Will generate a tree representation of the file system starting from the current directory.

File/directory create, copy and remove

Command

Utility

cp -p source destination

Will copy the file from source to destination. -p stands for preservation. It

preserves the original attributes of file while copying like file owner, timestamp,

group, permissions etc.

cp -R source_dir

destination_dir

mv file1 file2

rm -i filename

Will copy source directory to specified destination recursively.

In Linux there is no rename command as such. Hence mv moves/renames the

file1 to file2.

Asks you before every file removal for confirmation. IF YOU ARE A NEW USER

TO LINUX COMMAND LINE, YOU SHOULD ALWAYS USE rm -i. You can specify

multiple files.

rm -R dir-name

Will remove the directory dir-name recursively.

rm -rf dir-name

rmdir dir-name

Will remove the directory dir recursively, ignoring non-existent files and will

never prompt for anything. BE CAREFUL USING THIS COMMAND! You can

specify multiple directories.

Will remove the directory dir-name, if it's empty. This command can only remove

empty directories.

mkdir dir-name

Create a directory dir-name.

mkdir -p dir-name/dir-name

Create a directory hierarchy. Create parent directories as needed, if they don't

exist. You can specify multiple directories.

touch filename

Create a file filename, if it doesn't exist, otherwise change the timestamp of the

file to current time.

File/directory permissions and groups

Command

Utility

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chmod <specification> filename

Change the file permissions. Specifications = u user, g group, o other, + add

permission, - remove, r read, w write,x execute.

chmod -R <specification> dir-

name

Change the permissions of a directory recursively. To change permission of

a directory and everything within that directory, use this command.

chmod go=+r myfile

chmod a +rwx myfile

chmod go -r myfile

Add read permission for the owner and the group.

Allow all users to read, write or execute myfile.

Remove read permission from the group and others.

chown owner1 filename

Change ownership of a file to user owner1.

chgrp grp_owner filename

Change primary group ownership of file filename to group grp_owner.

chgrp -R grp_owner dir-name

Change primary group ownership of directory dir-name to group grp_owner

recursively. To change group ownership of a directory and everything within

that directory, use this command.

Section 1.3: Hello World

Type the following code into your terminal, then press Enter :

echo "Hello World"

This will produce the following output:

Hello World

Section 1.4: Basic Linux Utilities

Linux has a command for almost any tasks and most of them are intuitive and easily interpreted.

Getting Help in Linux

Command

Usability

man <name>

Read the manual page of <name>.

man <section> <name>

Read the manual page of <name>, related to the given section.

man -k <editor>

man -K <keyword>

apropos <editor>

help

help <name>

info <name>

dpkg -l

Output all the software whose man pages contain <editor> keyword.

Outputs all man pages containing <keyword> within them.

Output all the applications whose one line description matches the word editor.

When not able to recall the name of the application, use this command.

In Bash shell, this will display the list of all available bash commands.

In Bash shell, this will display the info about the <name> bash command.

View all the information about <name>.

Output a list of all installed packages on a Debian-based system.

dpkg -L packageName

Will list out the files installed and path details for a given package on Debian.

dpkg -l | grep -i <edit>

Return all .deb installed packages with <edit> irrespective of cases.

less /var/lib/dpkg/available Return descriptions of all available packages.

whatis vim

List a one-line description of vim.

<command-name> --help

Display usage information about the <tool-name>. Sometimes command -h also

works, but not for all commands.

User identification and who is who in Linux world

Command

hostname

Display hostname of the system.

Usability

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hostname -f Displays Fully Qualified Domain Name (FQDN) of the system.

passwd

whoami

who

w

last

Change password of current user.

Username of the users logged in at the terminal.

List of all the users currently logged in as a user.

Display current system status, time, duration, list of users currently logged in on system and other

user information.

Who recently used the system.

last root When was the last time root logged in as user.

lastb

chmod

Shows all bad login attempts into the system.

Changing permissions - read,write,execute of a file or directory.

Process related information

Command

top

ps

List all processes sorted by their current system resource usage. Displays a continually updated

display of processes (By default 3 seconds). Use q key to exit top.

List processes currently running on current shell session

Usability

ps -u root List all of the processes and commands root is running

ps aux

List all the processes by all users on the current system

Section 1.5: Searching for files by patterns in name/contents

A common and task of someone using the Linux Command Line (shell) is to search for files/directories with a

certain name or containing certain text. There are 2 commands you should familiarise yourself with in order to

accomplish this:

Find files by name

find /var/www -name '*.css'

This will print out the full path/filename to all files under /var/www that end in .css. Example output:

/var/www/html/text-cursor.css

/var/www/html/style.css

For more info:

man find

Find files containing text

grep font /var/www/html/style.css

This will print all lines containing the pattern font in the specified file. Example output:

font-weight: bold;

font-family: monospace;

Another example:

grep font /var/www/html/

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This doesn't work as you'd hoped. You get:

grep: /var/www/html/: Is a directory

You need to grep recursively to make it work, using the -R option:

grep -R font /var/www/html/

Hey nice! Check out the output of this one:

/var/www/html/admin/index.php: echo '<font color=red><b>Error: no dice</b></font><br/>';

/var/www/html/admin/index.php: echo '<font color=red><b>Error: try again</b></font><br/>';

/var/www/html/style.css: font-weight: bold;

/var/www/html/style.css: font-family: monospace;

Notice that when grep is matching multiple files, it prefixes the matched lines with the filenames. You can use the -

h option to get rid of that, if you want.

For more info:

man grep

Section 1.6: File Manipulation

Files and directories (another name for folders) are at the heart of Linux, so being able to create, view, move, and

delete them from the command line is very important and quite powerful. These file manipulation commands allow

you to perform the same tasks that a graphical file explorer would perform.

Create an empty text file called myFile:

touch myFile

Rename myFile to myFirstFile:

mv myFile myFirstFile

View the contents of a file:

cat myFirstFile

View the content of a file with pager (one screenful at a time):

less myFirstFile

View the first several lines of a file:

head myFirstFile

View the last several lines of a file:

tail myFirstFile

Edit a file:

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vi myFirstFile

See what files are in your current working directory:

ls

Create an empty directory called myFirstDirectory:

mkdir myFirstDirectory

Create multi path directory: (creates two directories, src and myFirstDirectory)

mkdir -p src/myFirstDirectory

Move the file into the directory:

mv myFirstFile myFirstDirectory/

You can also rename the file:

user@linux-computer:~$ mv myFirstFile secondFileName

Change the current working directory to myFirstDirectory:

cd myFirstDirectory

Delete a file:

rm myFirstFile

Move into the parent directory (which is represented as ..):

cd ..

Delete an empty directory:

rmdir myFirstDirectory

Delete a non-empty directory (i.e. contains files and/or other directories):

rm -rf myFirstDirectory

Make note that when deleting directories, that you delete ./ not / that will wipe your whole filesystem.

Section 1.7: File/Directory details

The ls command has several options that can be used together to show more information.

Details/Rights

The l option shows the file permissions, size, and last modified date. So if the root directory contained a dir called

test and a file someFile the command:

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user@linux-computer:~$ ls -l

Would output something like

-rw-r--r-- 1 user users 70 Jul 22 13:36 someFile.txt

drwxrwxrwx 2 user users 4096 Jul 21 07:18 test

The permissions are in format of drwxrwxrwx. The first character represents the file type d if it's a directory -

otherwise. The next three rwx are the permissions the user has over the file, the next three are the permissions the

group has over the file, and the last three are the permissions everyone else has over the file.

The r of rwx stands for if a file can be read, the w represents if the file can be modified, and the x stands for if the

file can be executed. If any permission isn't granted a - will be in place of r, w, or x.

So from above user can read and modify someFile.txt but the group has only read-only rights.

To change rights you can use the chmod ### fileName command if you have sudo rights. r is represented by a

value of 4, w is represented by 2, and x is represented by a 1. So if only you want to be able to modify the contents

to the test directory

Owner rwx = 4+2+1 = 7

Group r-x = 4+0+1 = 5

Other r-x = 4+0+1 = 5

So the whole command is

chmod 755 test

Now doing a ls -l would show something like

drwxr-xr-x 2 user users 4096 Jul 21 07:20 test

Readable Size

Used in conjunction with the l option the h option shows file sizes that are human readable. Running

user@linux-computer:~$ ls -lh

Would output:

total 4166

-rw-r--r-- 1 user users 70 Jul 22 13:36 someFile.txt

drwxrwxrwx 2 user users 4.0K Jul 21 07:18 test

Hidden

To view hidden files use the a option. For example

user@linux-computer:~$ ls -a

Might list

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.profile

someFile.txt

test

Total Directory Size

To view the size of the current directory use the s option (the h option can also be used to make the size more

readable).

user@linux-computer:~$ ls -s

Outputs

total 4166

someFile.txt test

Recursive View

Lets say test directory had a file anotherFile and you wanted to see it from the root folder, you could use the R

option which would list the recursive tree.

user@linux-computer:~$ ls -R

Outputs

.:

someFile.txt test

./test:

anotherFile

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Chapter 2: Detecting Linux distribution

name and version

Section 2.1: Detect what debian-based distribution you are

working in

Just execute lsb_release -a.

On Debian:

$ lsb_release -a

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