Installing Lynis

In this quick tutorial, we’re going to take a look at how we can append multiline strings to a file using the tools provided by our command shell.

For simplicity we’ll use the same set of test data in all the examples:

Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

The commands used in this tutorial were tested in Bash but should work in other POSIX-compliant shells as well, unless specified otherwise.

2. echo

We can redirect the output of echo and append it to our file using the redirection operator >>. A new line is inserted automatically when the file doesn’t exist and is not empty.

Therefore a naive solution to our problem would be to call echo twice, once for each line that we need to append:

echo Lorem ipsum dolor sit amet, consectetur adipiscing elit, >> target.txt
echo sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. >> target.txt

Let’s further simplify this and use a oneliner by explicitly inserting the newline character \n. We use the -e argument to force evaluation, which is required when we execute the statement within a script:

echo -e Lorem ipsum dolor sit amet, consectetur adipiscing elit,\\nsed do eiusmod \
tempor incididunt ut labore et dolore magna aliqua. >> target.txt

In the above example, we have to explicitly escape the \ with another \. However, we can avoid this by surrounding our string with double quotes, which is regarded as best practice:

echo -e "Lorem ipsum dolor sit amet, consectetur adipiscing elit,\nsed do eiusmod \
tempor incididunt ut labore et dolore magna aliqua." >> target.txt

It’s important to note that the echo command has one serious drawback. Many shells provide their own version of echo. Consequently, implementations are not always POSIX-compliant and can differ between shells.

3. printf

Let’s now take a look at the printf command. This command works the same in every POSIX-compliant shell and can be used in the same way as echo:

printf "Lorem ipsum dolor sit amet, consectetur adipiscing elit,\nsed do eiusmod \
tempor incididunt ut labore et dolore magna aliqua." >> target.txt

Furthermore, the printf command is more advanced and can be used to format strings as well.

It’s similar to the C-function that goes by the same name. For example, we can use a C-style string format like this:

printf "%s\n%s" "Lorem ipsum dolor sit amet, consectetur adipiscing elit," \
"sed do eiusmod tempor incididunt ut labore et dolore magna aliqua."

More information about formatting strings can be found in the comprehensive man pages.

4. cat

There are solutions to our problem that are less obvious.

For example, we can use the cat command for appending lines to a file. Normally, we use this command to concatenate files and print their contents to the standard output.

However, if we omit the file argument, cat will read input from the standard input. Then we can use cat to append text:

cat << EOF >> target.txt
Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
EOF

In this example, << EOF means that we want cat to read from the standard input until it encounters a line only containing the text EOF (end of file). Likewise, the output of cat is written to target.txt in the same way as in previous examples, using the >> redirection operator.

5. tee

Simply put, the tee command takes standard input and copies it to standard output, also making copies of it in zero or more files. We can use tee in a similar way to how we used cat previously.

For example, we can tell tee to append (-a) standard input to our file until EOF is encountered:

tee -a target.txt << EOF
Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
EOF

6. Conclusion

In this quick tutorial, we looked at how we can use default shell commands to append multiline strings to a file.

We began by looking at the echo and printf commands which are the most obvious solutions. Then, we showed how we can achieve similar results using two less common approaches using the cat and tee commands.

The post Linux Commands for Appending Multiple Lines to a File appeared first on Tech Chronicles.

xz -d ubuntu-mate-18.04.2-beta1-desktop-armhf+raspi-ext4.img.xz

cd Download

sudo dd bs=1m if=ubuntu-mate-18.04.2-beta1-desktop-armhf+raspi-ext4.img of=/dev/rdisk1 conv=sync

sudo apt update
sudo apt upgrade

The post How to Install Ubuntu Mate on Raspberry Pi 2 or 3 appeared first on Tech Chronicles.

This post describes how to obtain Linux Privilege Escalation through SUDO abuse.

The tool can be used by pentesters, system admins, CTF players, students, System Auditors and trolls :).


INTRO
**WARNING: SUDO_KILLER is part of the KILLER project. SUDO_KILLER is still under development and there might be some issues, please create an issue if you found any. **
Other tool will be added to the KILLER project in the coming months so stay tuned up.

Overview
SUDO_KILLER is a tool that can be used for privilege escalation on linux environment by abusing SUDO in several ways. The tool helps to identify misconfiguration within sudo rules, vulnerability within the version of sudo being used (CVEs and vulns) and the use of dangerous binary, all of these could be abused to elevate privilege to ROOT.
SUDO_KILLER will then provide a list of commands or local exploits which could be exploited to elevate privilege. It is worth noting that the tool does not perform any exploitation on your behalf, the exploitation will need to be performed manually and this is intended.

Features

Some of the checks/functionalities that are performed by the tool:

• Misconfigurations
• Dangerous Binaries
• Vulnerable versions of sudo – CVEs
• Dangerous Environment Variables
• Credential Harvesting
• Writable directories where scripts reside
• Binaries that might be replaced
• Identify missing scripts

What version 2 of SK includes:

• New checks and/or scenarios:

1. CVE-2019-14287 – runas
2. No CVE yet – sudoedit – absolute path
3. CVE-2019-18634 – pwfeedback
4. User Impersonation
5. list of users in sudo group

• Performance improved
• Bugs corrected (checks, export, report,…)
• Continous improvement of the way output presented
• New videos will be added soon
• Annonying password input several time removed
• New functionality: offline mode – ability to extract the required info from audited system and run SK on host.
• Testing environment : A docker to play with the tool and different scenarios, you can also train on PE.

Usage

Example Online mode

./sudo_killer.sh -c -e -r report.txt -p /tmp

Example Offline mode
Run extract.sh on system to be audited/victim machine. Copy the output from /tmp/sk_offline.txt on the system to be audited/victim machine to your host.

• Note: Three checks are missing in the offline mode, still in dev… coming soon…

Run SK with the below parameter:

./sudo_killer.sh -c -i /path/sk_offline.txt

Optional arguments

• -c : include CVE checks with respect to sudo version
• -i : import (offline mode) from extract.sh
• -e : include export of sudo rules / sudoers file
• -r : report name (save the output)
• -p : path where to save export and report
• -s : supply user password for sudo checks (not recommended ++except for CTF)
• -h : help

CVEs check
To update the CVE database : run the following script ./cve_update.sh

Providing password (Important)
If you need to input a password to run sudo -l then the script will not work if you don’t provide a password with the argument -s.

How to run SK on the targetted/audited machine
If you are on a machine that has internet connection, just git clone the tool and run it. If you are on a machine that does not have internet, then git clone on your host, compress the tool (tar) then transfert the compressed file via http/smb (apache web server / python simplehttpserver / smb server / nc) then uncompressed the file on the targeted system and enjoy!

Notes
**NOTE : sudo_killer does not exploit automatically by itself, it was designed like this on purpose but check for misconguration and vulnerabilities and then propose you the following (if you are lucky the route to root is near!) :

• a list of commands to exploit
• a list of exploits
• some description on how and why the attack could be performed

Why is it possible to run “sudo -l” without a password?
By default, if the NOPASSWD tag is applied to any of the entries for a user on a host, he or she will be able to run “sudo -l” without a password. This behavior may be overridden via the verifypw and listpw options.
However, these rules only affect the current user, so if user impersonation is possible (using su) sudo -l should be launched from this user as well.
Sometimes the file /etc/sudoers can be read even if sudo -l is not accessible without password.

Docker – Vulnerable testing environment
**IMPORTANT: The recommended way to test the tool is to use the docker image created on purpose for the testing. The image contained several vulnerabilities and misconfigurations related to the usage of SUDO.
Everything is tested from the Docker container available on Docker Hub !**

A Docker image is available on Docker Hub and automatically re-built at each update: https://hub.docker.com/r/th3xace/sudo_killer_demo . It is initially based on official debian:jessie Docker image (debian:jessie).

1. Pull SUDO_KILLER_DEMO Docker Image from the docker hub (This version maybe a bit more up-to-date):
   

   service docker start
   docker pull th3xace/sudo_killer_demo
   docker run --rm -it th3xace/sudo_killer_demo

2. Build locally from Dockerfile :
   

   service docker start
   git clone https://github.com/TH3xACE/SUDO_KILLER.git
   cd SUDO_KILLER
   docker build -t th3xace/sudo_killer_demo .
   docker run --rm -it th3xace/sudo_killer_demo

Note: It is important to note that the docker is just an environment that can be used to play with the tool since it contains several vulns to exploit. The tool is meant to be used on its own.

Demos
Several videos are provided below with different scenarios of exploitation.

Disclaimer
This script is for Educational purpose ONLY. Do not use it without permission. We are not liable for any damages caused by direct or indirect use of the information or functionality provided by these programs. The author or any Internet provider bears NO responsibility for content or misuse of these programs or any derivatives thereof. By using these programs you accept the fact that any damage (dataloss, system crash, system compromise, etc.) caused by the use of the script is not our responsibility.

Download SUDO_KILLER

The post SUDO_KILLER – A Tool To Identify And Exploit Sudo Rules’ Misconfigurations And Vulnerabilities Within Sudo appeared first on Tech Chronicles.

Do you prefer terminal emulators over GUI? But there are times when the terminal’s decent styling seems boring. In such cases, you look for more options to customize the terminal just like we do while choosing Linux distros.

If that’s the case, your wait is over as we bring the list of best terminal emulators for Linux that you can use to refresh your monotonous daily work. Along with the styling, you can also turn the single terminal into a multigrid, observing the activity of each terminal simultaneously.

Before you hop on the list, if you’re not familiar with a terminal emulator, let’s first understand what the terminal emulator is.

What is A Terminal Emulator?

A terminal emulator is a software similar to other GUIs applications with functionality to enable communication with your host computer. Let’s not confuse between the Terminal and Terminal Emulator. Terminal represents a piece of hardware, i.e., keyboard/monitor, while the Terminal emulator mimics a terminal through which a user gives a command to perform an action.

Terminal Emulator is a GUI application program that allows windows to take input and display output to the user in text format. Multiple terminal window programs can be included in the system.

Moving forward, let’s look at the best terminal emulators available. We’ve compiled the list based on various parameters such as color support, fonts, customization, lightweight, etc.

Top 10 Linux Terminal Emulators

1. Terminator

Terminator is the first non-default Linux terminal emulator that I tried and am still relying upon it. Terminator first introduced me to the better arrangement of terminals in a grid-like structure.

The best part that I like about terminator is that it lets you open multiple terminals either in vertical or horizontal mode and monitor the activity of each terminal at the same time.

Key highlighting features of Terminator:

• Multigrid-like structure
• Save multiple layouts and profiles
• Terminal reordering using drag and drop
• Third-party plugins

The default and classic emulator always restrict you to single screen monitoring; however, you can open a new tab or new terminal. But multiple terminals in a separate window give more control and comfort.

Terminator is inspired by gnome-multi-term and much of the behavior is borrowed from GNOME terminal. Moreover, you can also number the terminal and create a group of the terminal.

How to install?

You can run the command below to install the Terminator.

sudo apt install terminator

Note: All the given commands are based on Debian-based Linux distros. You can replace the command with your running distros package manager. This applies to all the installation instructions mentioned ahead in this article.

If you find any error like “unable to locate package”, then you need to add terminator PPA into your package manager repository by running the command:

sudo add-apt-repository ppa:gnome-terminator

2.  Terminology

The name may look similar to terminator but terminology stands way apart from the Terminator. Terminology uses the elementary toolkit to give cutting edge design to the terminal user interface.

Key highlighting features of terminology:

• Understand the full file path, URL links, and email address
• Local file display
• Configuration panel
• Display progress bar for downloads

Terminology is the most stylish and powerful emulator that also offers various pre-installed themes and wallpaper.

Using Enlightenment Foundation Libraries (EFL), Terminology works in X11 and Wayland windowing system and allows the video engine to run inside the terminal.

Another feature that will excite you is the lighting effect from the corner side while pressing the backspace keypad and glittering rectangular cursor.

To add more comfortability, Terminology also layouts the control panel with buttons to open and modify the behavior of the terminal.

How to install?

For quick installation of Terminology, you can run the command:

sudo apt install terminology

If you find any error, you can check out the list of dependencies from here that you need to install.

3. Cool Retro Term

If you’re a 90s’ kid and want to dig into your past where you had big back tv with flickering cathode screen, you would definitely love the cool retro term Linux emulator.

The cool retro term is mainly focused on simulating the style of the 90s cathode ray screen with a color variant. The visual look is seamlessly attractive with an outwardly raised concave screen.

Key highlighting features of Cool Retro Term:

• Old Cathode display
• Customizable, and reasonably lightweight
• Vintage visual settings

The typing cursor also ignites with yellow flash during typing commands, and the flickering line runs from top to bottom.

The cool retro term comes in various visual settings such as Default Amber, IBM DOS, Monochrome Green, Vintage, and Futuristic. It uses the QTermWidget terminal widget that also powers the ubuntu-terminal-app.

The cool retro term is also available for macOS. You can download it from here and follow the instructions as given for each Linux distro.

How to install?

For quick installation of cool retro term, you can run the command:

sudo apt install cool-retro-term

If you find errors like “Unable to locate the package,” you can get the package or AppImage of cool-retro-term from here.

4. KDE – Konsole

Konsole is the default terminal emulator for the KDE desktop environment. Hence, it uses KDE Framework, QT library, and xcb windowing system.

Key highlighting features of Konsole:

• Multi-language
• Bookmark Tab
• Multiple profiles with its own configuration
• Multi-tab for each window

The unique feature that Konsole offers is the native languages. If you love your local language, you can switch to your own choice of primary language such as Hindi, Punjabi, Arabic, Russian, etc. Konsole also provides the facility for default fallback language.

If you want to save your current location path, you can also bookmark the tab and store it in the folder.

But if you want to open multiple terminals to form grid structure, you may find it hard as KDE lacks to split view in left/right or top/bottom simultaneously. However, you can open multiple tabs in each window terminal.

How to install?

For a quick installation of Konsole, you can run the command:

sudo apt install konsole

5. Tilix

Tilix has one of the best default stylings, which may look similar to GNOME. But Tilix is way better with the menu button available to open terminal right or down to form the grid structure.

Key highlighting features of Tilix:

• Multi-session creation
• Custome titles
• Background image
• Process completion notification

Tilix allows creating a single or group of a session window with each having its own configurations. You can also save the current session and load from the system.

You can also create multiple panels by splitting the terminal vertically or horizontally.

How to install?

For quick installation of Tilix, you can run the command:

sudo apt install tilix

Tilix is mostly available in every Linux distros repository. But if you find any difficulty, you can check out the instructions given here.

6.  Guake

I find Guake very amazing as it allows me to run the instant command without hiding my current application window. Guake is one of the best drop-down Linux terminal emulators for the GNOME desktop environment.

There are also other drop-down terminal emulators such as Yakuake, part of KDE family, and Tilda, but they have minimal customization. Guake is highly inspired from the Quake emulator.

Key highlighting features of Guake:

• Instant access to a terminal with a single keystroke
• Autoconfigure and script execution at the login

You can swiftly pull the terminal from the top bar by pressing a single keypad. F12 is the default keystroke which you can change later. Terminal stacks over the current application instead of replacing it with new windows.

Moreover, you can also open multiple terminals and reset the color of the focused window.

How to install?

For quick installation of Guake, you can run the command:

sudo apt install guake

If you’re unable to install it, you can directly get the source code from the git repository from here and follow the installation guide.

7. GNOME

Ubuntu and its derivatives feature the GNOME desktop environment that comes with default GNOME terminal emulator. The default styling includes a decent green text hostname and light grey background.

Key highlighting features of GNOME:

• Custom cursor and font style
• Multi-tab and Fullscreen mode
• Script execution on startup
• Audible notification

Apart from the general appearance settings, you can also create various profiles with specific customized setting values. You can also perform multiple tasks using personalized shortcuts.

You can also customize the default terminal window size and zoom in or out to change the text size.

GNOME adds fluency to work with text as it understands the hyperlinks and email addresses, which redirects to the corresponding application to open.

How to install?

For quick installation of GNOME terminal, you can run the command:

sudo apt install gnome-terminal

8. Xfce

Xfce desktop environment is known for its lightweight experience that ships with the Xfce4-terminal emulator. Xfce emulator is mainly focussed on running over the old hardware devices.

Key highlighting features of Xfce4-terminal:

• Export output in a plain text file
• Change terminal title

Xfce4-terminal allows opening multiple tabs but is restricted to the individual terminal at a time. You need to use a mouse pointer to switch between tabs to monitor the multiple terminal actions at once.

Xfce emulator is based on the Vte terminal widget library, like gnome-terminal. Similarly, Xfce does not provide many options to customize, except terminal preferences that include general and appearance settings.

How to install?

For quick installation of Xfce, you can run the command:

sudo apt install xfce4-terminal

If you find any difficulty, you can download the tarball source from here.

9. Alacritty

Alacritty is considered to be the fastest terminal emulator that uses your GPU to optimize the speed.

Alacritty is a cross-platform, performance focussed and simplest terminal emulator. Being the fastest, some people may find it the best emulator, but it also lags to offer the style customization options.

Key highlighting features of Alacritty:

• Cross-platform
• GPU accelerated
• Colored emojis

Another thing that you may dislike about the Alacritty is third party tool dependency. Installing Alacritty is a lengthy process that may initially force you to stay on the same emulator rather than struggle with the installation.

How to install?

If you’re using Debian-based Linux distro, you can install the alacritty using snapd application package.

sudo apt update
sudo apt install snapd
sudo snap install alacritty --classic

For other Linux distros, you can follow the command given here, or you can download the pre-built binaries from here.

10. Tilda

Tilda is also a drop-down emulator based on GTK with no border window. You can press the default F12 or customized keystroke to open the terminal that pulls out from the top.

Key highlighting features of Tilda:

• Dropdown
• Highly configurable
• Toggle search bar
• Auto-hide terminal

Tilda is limited to work only on Xorg-based desktops, and it does not support Wayland; hence doesn’t work on Ubuntu 17.10 onwards.

How to install?

For quick installation of Tilda, you can run the command:

sudo apt install tilda

If you find any difficulty, you can download the pre-built binaries or follow instructions given here.

So the list of top ten emulators ends here, but not the list of terminal emulators. You can also try other terminal emulators available such as Lilyterm, Tilda, eterm, roxterm, etc.

The post 10 Best Linux Terminal Emulators [2020 Edition] appeared first on Tech Chronicles.

New Linux converts coming from the Windows world may find working with the command line to be somewhat intimidating. However, it’s not that difficult to use. All you need to get started with the command line is to learn a few basic commands.

While most Linux distributions are user-friendly and come with an easy to use graphical interface, knowing how to use the command line can be very useful. The command line gives you more power over your system and access to features that are not available through a graphical interface.

In this article, we’ll go through some of the most common Linux commands that are used on a daily basis by the Linux system administrators.

Getting Information About the Command

Memorizing command options is usually not necessary and may be a waste of time. Usually, if you are not using the command frequently, you can easily forget its options.

Most commands have a --help option which prints a short message about how to use the command and exits:

command_name --help

Almost all Linux commands are distributed together with man pages. A man or manual page is a form of documentation that explains what the command does, examples of how you run the command, and what arguments it accepts.

The man command is used to display the manual page of a given command.

man command_name

man cd

To navigate the man pages, use the Arrow, Page Up and Page Down keys. You can also press Enter key to move one line at a time, the Space bar to move to the next screen, and the b key to go one screen back. To exit the man page, press the q key.

Navigating the File System

In Linux, every file and directory is under the root directory, which is the first or top-most directory in the directory tree. The root directory is referred to by a single leading slash /.

When navigating the file system on operating on files, you can use either the absolute or the relative path to the resource.

The absolute or full path starts from the system root /, and the relative path starts from your current directory.

Current Working Directory (pwd command)

The current working directory is the directory in which the user is currently working in. Each time you interact with your command prompt, you are working within a directory.

Use the pwd command to find out what directory you are currently in:

pwd

The command displays the path of your current working directory:

/home/linuxize

Changing directory (cd command)

The cd (“change directory”) command is used to change the current working directory in Linux and other Unix-like operating systems.

When used without any argument, cd will take you to your home directory:

cd

To change to a directory, you can use its absolute or relative path name.

Assuming that the directory Downloads exists in the directory from which you run the command, you can navigate to it by using the relative path to the directory:

cd Downloads

You can also navigate to a directory by using its absolute path:

cd /home/linuxize/Downloads

Two dots (..), one after the other, are representing the parent directory or, in other words, the directory immediately above the current one.

Suppose you are currently in the /usr/local/share directory, to switch to the /usr/local directory (one level up from the current directory), you would type:

cd ../

To move two levels up use:

cd ../../

To change back to the previous working directory, use the dash (-) character as an argument:

cd -

If the directory you want to change to has spaces in its name, you should either surround the path with quotes or use the backslash () character to escape the space:

cd Dir\ name\ with\ space

Working with Files and Directories

Listing directory contents (ls command)

The ls command is used to list information about files and directories within a directory.

When used with no options and arguments, ls displays a list in alphabetical order of the names of all files in the current working directory:

ls

To list files in a specific directory, pass the path to the directory as an argument:

ls /usr

The default output of the ls command shows only the names of the files and directories. Use the -l to print files in a long listing format:

ls -l /etc/hosts

The output includes the file type, permissions, number of hard links, owner, group, size, date, and filename:

-rw-r--r-- 1 root root 337 Oct  4 11:31 /etc/hosts

The ls command doesn’t list the hidden files by default. A hidden file is any file that begins with a period (.).

To display all files including the hidden files, use the -a option:

ls -a ~/

Displaying file contents (cat command)

The cat command is used to print the contents of one or more files and to merge (concatenate) files by appending the contents of one file to the end of another file.

To display the contents of a file on the screen, pass the file name to cat as an argument:

cat /etc/hosts

Creating files (touch command)

The touch command is used to update the timestamps on existing files and directories as well as to create new, empty files.

To create a file, specify the file name as an argument:

touch file.txt

If the file already exists, touch will change the file last access and modification times to the current time.

Creating directories (mkdir command)

In Linux, you can create new directories (also known as folders) using the mkdir command.

To create a directory, pass the name of the directory as the argument to the command:

mkdir /tmp/newdirectory

mkdir can take one or more directory names as its arguments.

When providing only the directory name, without the full path, it will be created in the current working directory.

To create parent directories use the -p option:

mkdir -p Projects/linuxize.com/src/assets/images

The command above creates the whole directory structure.

When mkdir is invoked with the -p option, it creates the directory only if it doesn’t exist.

Creating symbolic links (ln command)

A symbolic link (or symlink) is a special type of file that points to another file or directory.

To create a symbolic link to a given file, use the ln command with the -s option, the name of the file as the first argument and the name of the symbolic link as the second argument:

ln -s source_file symbolic_link

If only one file is given as an argument ln creates a link to that file in the current working directory with the same name as the file it points to.

Removing files and directories (rm command)

To remove files and directories use the rm command.

By default, when executed without any option, rm doesn’t remove directories. It also doesn’t prompt the user for whether to proceed with the removal of the given files.

To delete a file or a symlink, use the rm command followed by the file name as an argument:

rm file.txt

rm accepts one or more file or directory names as its arguments.

The -i option tells rm to prompt the user for each given file before removing it:

rm -i file.txt

rm: remove regular empty file 'file.txt'? 

Use the -d option to remove one or more empty directories:

rm -d dirname

To remove non-empty directories and all the files within them recursively, use the -r (recursive) option:

rm -rf dirname

The -f option tells rm never to prompt the user and to ignore nonexistent files and arguments.

Copying files and directories (cp command)

The cp command allows you to copy files and directories.

To copy a file in the current working directory, use the source file as a first argument and the new file as the second:

cp file file_backup

To copy a file to another directory, specify the absolute or the relative path to the destination directory. When only the directory name is specified as a destination, the copied file will have the same name as the original file.

cp file.txt /backup

By default, if the destination file exists, it will be overwritten.

To copy a directory, including all its files and subdirectories, use the -R or -r option:

cp -R Pictures /opt/backup

Moving and renaming files and directories (mv command)

The mv command (short from move) is used to rename and move and files and directories from one location to another.

For example to move a file to a directory you would run:

mv file.txt /tmp

To rename a file you need to specify the destination file name:

mv file.txt file1.txt

The syntax for moving directories is the same as when moving files.

To move multiple files and directories at once, specify the destination directory as the last argument:

mv file.tx1 file1.txt /tmp

Installing and Removing Packages

A package manager is a tool that allows you to install, update, remove, and otherwise manage distro-specific software packages.

Different Linux distributions have different package managers and package formats.

Only root or user with sudo privileges can install and remove packages.

Ubuntu and Debian (apt command)

Advanced Package Tool or APT is a package management system used by Debian-based distributions.

There are several command-line package management tools in Debian distributions with apt and apt-get being the most used ones.

Before installing a new package first, you need to update the APT package index:

apt update

The APT index is a database that holds records of available packages from the repositories enabled in your system.

To upgrade the installed packages to their latest versions run:

apt upgrade

Installing packages is as simple as running:

apt install package_name

To remove an installed package, enter:

apt remove package_name

CentOS and Fedora (dnf command)

RPM is a powerful package management system used by Red Hat Linux and its derivatives such as CentOS and Fedora. RPM also refers to the rpm command and .rpm file format.

To install a new package on Red Hat based distributions, you can use either yum or dnf commands:

dnf install package_name

Starting from CentOS 8 dnf replaced yum as the default package manager. dnf is backward compatible with yum.

To upgrade the installed packages to their latest versions, type:

dnf update

Removing packages is as simple as:

dnf remove package_name

File Ownership and Permissions

In Linux, access to the files is managed through the file permissions, attributes, and ownership. This ensures that only authorized users and processes can access files and directories.

In Linux, each file is associated with an owner and a group and assigned with permission access rights for three different classes of users:

• The file owner.
• The group members.
• Everybody else.

There are three permissions types that apply to each class:

• The read permission.
• The write permission.
• The execute permission.

This concept allows you to specify which users are allowed to read the file, write to the file, or execute the file.

To view the file owner and permissions, use the ls -l command.

Changing permissions (chmod command)

The chmod command allows you to change the file permissions. It works in two modes, symbolic and numeric.

When using the numeric mode, you can set the permissions for the owner, group, and all others. Each write, read, and execute permissions have the following number value:

• r (read) = 4
• w (write) = 2
• x (execute) = 1
• no permissions = 0

The permissions number of a specific user class is represented by the sum of the values of the permissions for that group.

For example, to give the file’s owner read and write permissions and only read permissions to group members and all other users you would run:

chmod 644 filename

Only root, the file owner, or user with sudo privileges can change the permissions of a file.

To recursively operate on all files and directories under a given directory, use the chmod command with the -R, (–recursive) option:

chmod -R 755 dirname

Be extra careful when recursively changing the files’ permissions.

Changing ownership (chown command)

The chown command allows you to change the user and group ownership of a given file, directory, or symbolic link.

To change the owner of a file, use the chown command followed by the user name of the new owner and the target file:

chown username filename

To change both the owner and the group of a file invoke the chown command followed by the new owner and group separated by a colon (:) with no intervening spaces and the target file:

chown username:groupname filename

Use the -R (--recursive) option, to recursively operate on all files and directories under the given directory:

chown -R username:groupname dirname

Elevate privileges (sudo command)

The sudo command allows you to run programs as another user, by default the root user. If you spend a lot of time on the command line, sudo is one of the commands that you will use quite frequently.

Using sudo instead of login in as root is more secure because you can grant limited administrative privileges to individual users without them knowing the root password.

To use sudo, simply prefix the command with sudo:

sudo command

Managing Users and Groups

Linux is a multi-user system, which means that more than one person can interact with the same system at the same time. Groups are used to organize and administer user accounts. The primary purpose of groups is to define a set of privileges such as reading, writing, or executing permission for a given resource that can be shared among the users within the group.

Creating users (useradd and passwd Commands)

The useradd command allows you can create new users.

To create a new user account use the useradd command followed by the username:

useradd newuser

Once the user is created, set the user password by running the passwd command:

passwd newuser

Removing users (userdel Command)

In Linux, you can delete a user account using the userdel command.

To delete a user account named pass the user name to the userdel command:

userdel newuser

Use the -r (–remove) option to remove the user’s home directory and mail spool:

userdel -r newuser

Managing groups (groupadd and groupdel Command)

To create a new group use the groupadd command followed by the group name:

groupadd mygroup

To remove a group use the groupdel command with the group name as argument:

groupdel mygroup

Adding users to groups (usermod Command)

To add an existing user to a group, use the usermod command followed by the -G option and the name of the group:

usermod -a -G sudo linuxize

Conclusion

We have covered some of the most used Gnu/Linux commands.

Although you can perform most of the development and system-related tasks using a graphical interface, the command line makes you more productive and able to get more done in less time.

The post Basic Linux Commands appeared first on Tech Chronicles.

The cat command is one of the most widely used commands in Linux. The name of the cat command comes from its functionality to concatenate files. It can read and concatenate files, writing their contents to the standard output. If no file is specified or if the input file name is specified as a single hyphen (-) it reads from the standard input.

Cat is most commonly used to display the contents of one or multiple text files, combine files by appending the contents of one file to the end of another file, and create new files.

In this tutorial, we will show you how to use the cat command through practical examples.

Cat Command Syntax

Before going into how to use the cat command, let’s start by reviewing the basic syntax.

The cat utility expressions take the following form:

cat [OPTIONS] [FILE_NAMES]

• OPTIONS – cat options. Use cat --help to view all available options.
• FILE_NAMES – Zero or more file names.

Displaying File Contents

The most basic and common usage of the cat command is to read the contents of files.

For example, the following command will display the contents of the /etc/issue file in the terminal:

cat /etc/issue

 

Redirect Contents of File

Instead of displaying the output to stdout (on the screen) you can redirect it to a file.

The following command will copy the contents of file1.txt to file2.txt using the (>) operator :

cat file1.txt > file2.txt

If the file2.txt file doesn’t exist, the command will create it. Otherwise, it will overwrite the file.

Use the (>>) operator to append the contents of file1.txt to file2.txt :

cat file1.txt >> file2.txt

Same as before, if the file is not present, it will be created.

Print Line Numbers

To display contents of a file with line numbers, use the -n option:

cat -n /etc/lsb-release

1	DISTRIB_ID=Ubuntu
2	DISTRIB_RELEASE=18.04
3	DISTRIB_CODENAME=bionic
4	DISTRIB_DESCRIPTION="Ubuntu 18.04.1 LTS"

Suppress Repeated Empty Lines

Use the -s option to omit the repeated empty output lines:

cat -s file.txt

Display TAB characters

The -T option allows you to visually distinguish between tabs and spaces.

cat -T /etc/hosts

127.0.0.1^Ilocalhost
127.0.1.1^Iubuntu1804.localdomain

The TAB characters will be displayed as ^I.

Display End of Lines

To display the invisible line ending character use the -e argument:

cat -e /etc/lsb-release

DISTRIB_ID=Ubuntu$
DISTRIB_RELEASE=18.04$
DISTRIB_CODENAME=bionic$
DISTRIB_DESCRIPTION="Ubuntu 18.04.1 LTS"$

The Line endings will be displayed as $.

Concatenating Files

When passing two or more file names as arguments to the cat command the contents of the files will be concatenated. cat reads the files in the sequence given in its arguments and displays the file’s contents in the same sequence.

For example, the following command will read the contents of file1.txt and file2.txt and display the result in the terminal:

cat file1.txt file2.txt

You can concatenate two or more text files and write them to a file.

The following command will concatenate the contents of file1.txt and file2.txt and write them to a new file combinedfile.txt using the (>) operator :

cat file1.txt file2.txt > combinedfile.txt

If the combinedfile.txt file doesn’t exist, the command will create it. Otherwise, it will overwrite the file.

To concatenate the contents of file1.txt and file2.txt and append the result to file3.txt to use the (>>) operator:

cat file1.txt file2.txt >> file3.txt

If the file is not present, it will be created.

When concatenating files with cat, you can use the same arguments as shown in the previous section.

Creating Files

Creating small files with cat it often easier than opening a text editor such as nano, Vim, Sublime Text or Visual Studio Code.

To create a new file, use the cat command followed by the redirection operator (>) and the name of the file you want to create. Press Enter, type the text and once you are done, press the CRTL+D to save the file.

In the following example, we are creating a new file named file1.txt:

cat > file1.txt

If a file named file1.txt is present, it will be overwritten. Use the ‘>>’ operator to append the output to an existing file.

cat >> file1.txt

Conclusion

The cat command can display, combine and create new file.

If you have any questions or feedback, feel free to leave a comment.

The post Cat Command in Linux appeared first on Tech Chronicles.