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Introduction

Symbolic links, also known as symlinks, are a fundamental part of Linux file system, and they allow users to create shortcuts to files or directories. A symbolic link is a file that points to another file or directory, and it allows users to access a file or directory without having to use its full path. However, sometimes a symbolic link can become broken or outdated, which can cause issues for system or user. In this article, we will explain how to find and identify broken symlinks in Linux, and provide some examples of how to fix them.

What is a Broken Symlink?

A broken symlink is a symbolic link that points to a file or directory that no longer exists. When a user tries to access a file or directory through a broken symlink, they will receive an error message indicating that file or directory cannot be found. Broken symlinks can occur for various reasons, such as file or directory being deleted or renamed, or symlink being created incorrectly.

Why are Broken Symlinks a Problem?

Broken symlinks can cause issues for system or user. For example, if a broken symlink is used in a script, it may cause script to fail or produce unexpected results. Additionally, broken symlinks can take up disk space, as they still exist as files on system even if they are not pointing to anything.

How to Find Broken Symlinks in Linux

To find broken symlinks in Linux, we can use find command with -type l and -xtype l options. -type l option specifies that we are searching for symbolic links, and -xtype l option specifies that we are searching for broken symbolic links. Here is command to find broken symlinks in current directory and its subdirectories −

find . -xtype l

This command will find all broken symlinks in current directory and its subdirectories and display their names.

We can also restrict search to a specific directory by replacing “.” in command with path to directory. For example, to find broken symlinks in /home/user directory, we can use following command −

find /home/user -xtype l

This command will find all broken symlinks in /home/user directory and its subdirectories and display their names.

In addition to displaying names of broken symlinks, we can also print out additional information, such as target of symlink and size of symlink file, by using -ls option. Here is an example command that displays names, targets, and sizes of broken symlinks in current directory and its subdirectories −

find . -xtype l -ls

This command will display a list of broken symlinks, their targets, and their sizes.

How to Fix Broken Symlinks in Linux

Once we have identified broken symlinks on our system, we can either delete them or fix them. To delete a broken symlink, we can use rm command followed by name of symlink. For example, to delete a broken symlink named “broken_link”, we can use following command −

rm broken_link

This command will delete broken symlink from file system.

To fix a broken symlink, we need to update symlink to point to a valid file or directory. To do this, we can use ln command with -sf options. -s option specifies that we are creating a symbolic link, and -f option specifies that we want to overwrite any existing file or directory with same name as symlink. Here is an example command that fixes a broken symlink named “broken”. To fix a broken symlink, we need to update symlink to point to a valid file or directory. To do this, we can use ln command with -sf options. -s option specifies that we are creating a symbolic link, and -f option specifies that we want to overwrite any existing file or directory with same name as symlink. Here is an example command that fixes a broken symlink named “broken_link” and points it to a valid file called “valid_file” −

ln -sf valid_file broken_link

This command will update broken symlink to point to valid file, and -f option will overwrite old symlink if it already exists.

We can also fix broken symlinks in bulk by using find command in conjunction with xargs command. find command can be used to find all broken symlinks, and xargs command can be used to pass list of broken symlinks to ln command to fix them. Here is an example command that fixes all broken symlinks in current directory and its subdirectories −

This command will find all broken symlinks in current directory and its subdirectories, and pass list of broken symlinks to ln command to fix them. readlink command is used to get target of each symlink, and -f option is used to get full path to target. {} placeholder is used to represent each broken symlink in list.

Conclusion

In conclusion, broken symlinks can cause issues for system or user, but they can be easily found and fixed using commands provided in this article. By using find command, we can identify all broken symlinks on our system, and by using ln command, we can fix them or delete them if necessary. It is important to regularly check for broken symlinks on our systems to ensure that they do not cause any issues and take up unnecessary disk space.

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How To Install And Configure Davinci Resolve In Linux

If you are a content creator, especially a video editor, then you have heard about DaVinci Resolve. DaVinci Resolve is known for its color correction capabilities in large film studios and comes with a powerful video and audio editor and composer, like Adobe After Effects, making it a go-to creative software among Linux creators. Unlike other creative software, DaVinci Resolve supports the Linux platform, so you don’t need any windows API translation layer like wine to install DaVinci Resolve.

Download Linux Binaries

Go to the DaVinci Resolve release page and download the latest version. At the time of writing, the latest version is version 18. DaVinci Resolve comes in two versions: free and paid. Select and download the Linux binaries and save them in your download folder.

Install Required Drivers

DaVinci Resolve is heavily dependent on GPU processing. If you have a recent Intel or AMD APU, then your integrated GPU may run DaVinci Resolve on your device. In most cases, you need an Nvidia GPU to run this software. Install the latest Nvidia drivers and CUDA for your Nvidia GPU in your Linux machine.

Install the Latest Nvidia Driver In Ubuntu

For Ubuntu-based distributions, it is very easy to install GPU drivers. Run these commands for rebooting to install the Nvidia GPU for you.

sudo

apt

search nvidia-driver

sudo

apt update

sudo

apt upgrade

sudo

apt

install

[

driver_name

]

Install the Latest Nvidia Driver in Debian

For Debian-based distributions, you have to do something more than run some commands. Open the “/etc/apt/sources.list” file:

sudo

nano

etc

apt

sources.list

Add this line in the chúng tôi file. If it’s already present, append the contrib and non-free component.

sudo

apt update

sudo

apt

install

nvidia-driver firmware-misc-nonfree

To install Cuda, you only need to run one command:

sudo

apt

install

nvidia-cuda-dev nvidia-cuda-toolkit

After installation, reboot your device so that the changes can take effect.

sudo

systemctl reboot Install the Latest Nvidia Driver in Fedora

To install the Nvidia driver in Fedora Linux, you first need to enable the RPM fusion repository.

sudo

dnf

update https:

download1.rpmfusion.org

nonfree

fedora

rpmfusion-nonfree-release-$

(

rpm

-E

fedora

)

.noarch.rpm

Detect the Nvidia GPU and install the required drivers.

sudo

dnf

install

akmod-nvidia

After installation, reboot your machine and you are good to go.

sudo

reboot Build a Deb Package

The DaVinci Resolve Linux build was released to run on CentOS, a RedHat-owned distribution. Therefore, If you are using Fedora or another RedHat distribution, you don’t need to follow the build step.

For Debian and Ubuntu-based distributions, you have to convert the DaVinci Resolve .run file into a .deb file.

To make this conversion possible, download and extract the MakeResolveDeb script.

Create a folder and copy the DaVinci Resolve Installer and MakeResolveDeb script into the folder.

Before the conversion, install some required dependencies to build and run DaVinci Resolve flawlessly.

sudo

apt

install

libssl1.1 ocl-icd-opencl-dev fakeroot xorriso

Run the following command to convert your .run file to a .deb file, assuming that you put both the script and .run installer into the same folder.

makeresolvedeb

.sh DaVinci_Resolve_

_Linux.run

It is quite an intensive process, so give your machine some time to extract and build the .deb package for you. When completed, you will be greeted with a .deb file ready to be installed.

Installing Deb Package

Installing a .deb file is really easy in Debian and Ubuntu derivatives. Run this command to install the package:

DaVinci Resolve Free vs. Paid

The DaVinci Resolve free version comes with all the basic features you need to edit your video, make motion graphics, color correct and edit your sounds.

All the studio features are required if you are working on a huge project, like filmmaking and documentaries. To make simple YouTube videos, the free version is enough for most users.

If you buy any Blackmagic gadgets, you get the studio version free of cost. If you are a professional video editor, consider buying the gadgets you may need.

Video Transcode to Use in Davinci Resolve

In the free version of DaVinci Resolve, the H264 codec is not supported. Therefore, if you record video using this codec, you have to transcode the video to another format that DaVinci Resolve supports. To transcode our video, we are using FFmpeg.

FFmpeg is a very powerful video transcoding and processing library and has many customization options. You can read the documentation to customize FFmpeg. To install it on your device, run the following command:

sudo

apt update

sudo

apt

install

ffmpeg

To edit your video inside DaVinci Resolve, you have to convert it to .mov format.

ffmpeg

-i

chúng tôi

-vcodec

dnxhd

-acodec

pcm_s16le

-s

1920x1080

-r

30000

1001

-b:v 36M -pix_fmt yuv422p

-f

mov chúng tôi the above command, it’s assumed your input file is “input.mp4” and the output file name is “output.mov.” You can change the names according to your preference.

To convert .mkv to .mp4, run the following command.

ffmpeg

-i

chúng tôi

-map

-vcodec

dnxhd -acodec:

pcm_s16le -acodec:

pcm_s16le

-s

1920x1080

-r

30000

1001

-b:v 36M -pix_fmt yuv422p

-f

mov chúng tôi Up OBS Studio for Davinci Resolve

If you want to edit your screen recordings using DaVinci Resolve and don’t want to transcode your recorded file every time you want to edit, then you have to change some settings in your OBS application.

Switch to the recording tab and change the output type to the custom output option (FFmpeg). Select “MOV” as the container format and “mpeg4” as a video encoder. In the audio encoder option, select the “pcm_s16le” option. You can refer to the settings below and make changes in your OBS software accordingly.

Save the settings and restart the OBS software. You can test if the settings are working or not by recording a little clip and importing it into your DaVinci Resolve software.

Transcode for Online Upload and Save Space

You can see that when we transcode the files to edit in DaVinci Resolve, the sizes are very big – sometimes hundreds of gigabytes. Therefore, editing and uploading the rendered file of a few hundred gigabytes takes a very long time. Even if you want to store the files on your hard disk, those sizes are very huge compared to their length.

To fix this issue, we are using FFmpeg to transcode and compress our file. Run the following command in your terminal:

ffmpeg

-i

chúng tôi

-vf

yadif -codec:v libx264

-crf

-bf

-flags

+cgop -pix_fmt yuv420p -codec:a aac

-strict

-2

-b:a 384k -r:a

48000

-movflags

faststart output.mp4

“input.mov” is your .mov file from DaVinci Resolve, and “output.mp4” is your output .mp4 file. You can change these names to your preference.

You can change the compression and output quality by adjusting the -crf flag. By default, I set it to 1, the highest quality. You can set this flag up to 25 for maximum compression. It also reduces video quality when -crf is a very high number.

Frequently Asked Questions Is DaVinci better than Premier?

It is about personal choice. If you are familiar with Premier, and your editing workflow revolves around Adobe software, then it is better to use Premier than Resolve. If you are a newbie and want to learn DaVinci Resolve, then you are good to go. If you are an M1 Mac owner, then DaVinci Resolve runs better in Apple M1 Macs.

Is 8GB RAM enough for DaVinci Resolve?

You need at least 16 GB of RAM to run DaVinci Resolve smoothly on your device. In addition to RAM, you need a powerful graphic card with 4GB or more VRAM to make your workflow smooth. I recommend that you invest in a desktop rather than a laptop.

Hrishikesh Pathak

Developer and writer. Write about linux and web.

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How To Create An Online Dictionary With Dico In Linux

Dico is a modern implementation of the traditional DICT protocol. It aims to create a fully modular dictionary server software that you can host almost anywhere. This tutorial shows how you can install and use Dico as your local “online” dictionary server in Linux.

Alternative: you can also install the SDCV dictionary app in the Linux terminal.

What Is an Online Dictionary and Why Use One?

Dictionary (DICT) servers are Internet programs that load and serve word definitions from an internal file. Unlike web dictionaries, DICT servers can be incredibly lightweight and flexible to changes, making it attractive for users that want to maintain their own dictionary at home.

Aside from that, modern DICT servers are also fully compatible with GNU Emacs, so you can create a Dico server, link it with GNU Emacs and load word definitions from inside the editor.

Lastly, DICT servers are also simple and easy to implement. Hosting one can be a good and fun starting point if you are a beginner at deploying Internet services.

Good to know: once you have your feet wet deploying server software, a good next step would be hosting your own Email server.

Installing GNU Dico

Run the following command to obtain GNU Dico’s dependencies.

sudo

apt

install

wget

gcc

make

m4-doc python3 libltdl-dev libdico2 zlib1g-dev

Download the GNU Dico source archive from the developer’s website:

Extract the program archive in your current working directory:

tar

xvJf .

dico-

2.11

.tar.xz

Go inside the program’s directory.

dico-

2.11

Run Dico’s initial configuration script:

configure

Start the program’s compilation process:

make

Install the program in your system’s “/usr/local/bin” directory:

sudo

make

install

Obtaining an Online Dictionary Database

Once you have installed the GNU Dico binary, download a dictionary database. It contains all the definitions that the program will serve once it is up and running.

One of the easiest ways to get a dictionary database is through the GNU Collaborative International Dictionary of English (GCIDE). It’s a free and open source collection of English words and definitions that spans back to 1913.

Download GCIDE from the maintainer’s website:

wget

ftp:

ftp.gnu.org

gnu

gcide

gcide-

0.53

.tar.xz

Extract the archive using tar:

tar

xvJf .

gcide-

0.53

.tar.xz

Copy the archive to your machine’s “/usr/local/share/” directory:

sudo

-rv

gcide-

0.53

usr

local

Configuring and Running GNU Dico

At this point, your system has a basic GNU Dico installation. For example, you can run dico in your terminal, and it will give you a basic prompt.

However, you still need to configure some of its settings to make it work properly for your machine.

Go to your “/usr/local/etc” directory:

usr

local

etc

Create the GNU Dico configuration file:

sudo

touch

dicod.conf

Open your new configuration file using your favorite text editor:

sudo

nano

dicod.conf

Add the following lines of code, a version of the default conf file that I have modified to work with GCIDE.

capability

(

mime,xversion

)

; timing

yes

; pidfile

var

run

dicod

dicod.pid; module-load-path

(

"/usr/local/lib/dico"

)

; load-module gcide; database

{

name

"gcide"

; handler

"gcide dbdir=/usr/local/share/gcide-0.53 suppress-pr"

; languages-from

"en"

; languages-to

"en"

;

}

user dicod; max-children

; inactivity-timeout

; server-info

<<EOT This is a Dico server. EOT

;

Save your configuration file by pressing Ctrl + O, then Ctrl + X.

Test your GNU Dico installation:

sudo

dicod

--foreground

Run an instance of the Dico console program by running dico on a separate terminal.

Type .open localhost to connect to the local Dico instance.

Test your new Dico server by sending any English word to the console prompt.

Configure GNU Dico to Autostart During Bootup

You can create a systemd service for GNU Dico, allowing you to easily manage your online dictionary and run it without a dedicated command line.

Create a systemd service file:

touch

personal-dicod.service

Open your new service file using your favorite text editor:

nano

personal-dicod.service

Add the following lines of code inside your service file:

[

Unit

]

Description

=A basic GNU Dico Daemon Service

[

Service

]

ExecStart

usr

local

bin

dicod

-f

--stderr

[

Install

]

WantedBy

=multi-user.target

Copy your service file to the systemd services directory:

sudo

personal-dicod.service

etc

systemd

system

Create the directory where dicod will store its pidfile:

sudo

mkdir

run

dicod

sudo

chown

-R

dicod:dicod

run

dicod

Reload systemd to apply your new configuration:

sudo

systemctl daemon-reload

Start your GNU Dico service by running the following commands:

sudo

systemctl

enable

personal-dicod.service

sudo

systemctl start personal-dicod.service

Tip: if you intend on running GNU Dico on a public network, secure your Linux server from malicious actors.

Linking GNU Dico to GNU Emacs

Aside from using the GNU Dico console, you can also integrate your new dictionary server to external applications. For example, easily link your Dico server with GNU Emacs by using the “dictionary.el” package.

To install the package, press Alt + X, then type “package-install.”

Type “dictionary” in the command buffer prompt.

After that, press Alt + X, then type “customize-variable.”

Type “dictionary-server” in the new buffer prompt.

Select the text box beside the “Dictionary Server” label and type localhost.

You can search your dictionary server by pressing Alt + X, then typing “dictionary-search” in the command buffer prompt.

FYI: Emacs is more than just a dictionary browser. Learn how you can also use it to create beautiful LaTeX documents without knowing any TeX code.

Frequently Asked Questions Dicod immediately terminates whenever I run it.

While this can be due to a number of issues, the most common cause for this is a misconfigured PID file. You can fix this by making sure that the dicod user and group exists in your system: sudo groupadd dicod && sudo useradd -s /usr/sbin/nologin -d /var/lib/dicod -g dicod dicod.

Also double check your “dicod.conf” file for any additional errors by running: dicod -t.

Is it possible to use a different online dictionary with GNU Dico?

Yes. However, you also need to make sure that Dico is loading the new dictionary’s module and database block in its “dicod.conf” file. For example, to use the chúng tôi database, you need to download a copy of its database files and load its module in your Dico configuration file.

Image credit: Unsplash. All alterations and screenshots by Ramces Red.

Ramces Red

Ramces is a technology writer that lived with computers all his life. A prolific reader and a student of Anthropology, he is an eccentric character that writes articles about Linux and anything *nix.

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How To Install Openrazer On Linux

One of the things that’s most frustrating about building a new computer for Linux is peripherals, especially for gamers who are looking for lots of functionality out of their peripherals. If you have Razer peripherals, you may be in luck, because the OpenRazer project has a solution for you. Here we go over how to install OpenRazer on Linux.

Getting Started

The first place you should go is the project’s chúng tôi page. You can see what devices are supported and learn more about the installation process. It’s fairly simple, but it does take a bit of time and planning.

Note: I have a Razer Basilisk Essential, which is in the process of being supported, but I’ll still demonstrate the process.

Installing OpenRazer

First, add the user you log in as to the plugdev group. This ensures you will have control over pluggable devices, like mice and keyboards. To do that, simply run the following command:

sudo

gpasswd

-a

$USER

plugdev

After that, you can follow the specific instructions for your distro that are listed on the page.

Arch Linux

For Arch users, openrazer is in the AUR, which is quite convenient. They suggest using pacaur to install in order to avoid dependency loops.

All Other Officially Supported Distros

All other officially supported distros should get their packages from the OpenSUSE build service. There are commands available for you to use, and they vary based on your distro. For Fedora, I’ll be running these commands:

sudo

dnf

install

openrazer-meta

For Ubuntu, run these commands:

sudo

apt update

sudo

apt

install

openrazer-meta

For OpenSuse, which seems to be the best supported, run these commands:

zypper refresh zypper

install

openrazer-meta

You can find the commands for your distro there.

For Community-Supported Distros

There are various communities that have stepped up and worked out different ways to support OpenRazer on their distros. You can reference the installation instructions on their website. Some distros like Solus and Void Linux have made it very simple.

Once you have OpenRazer installed, restart your computer, and you should be able to then install one of the graphical front ends listed on their website, which are Polychromatic, RazerGenie, razerCommander, and Snake.

Troubleshooting General

Make sure you add your user to the plugdev group. Some distros might not have it, but it’s a really important step that allows your user to control those devices.

Also, if you’re having trouble with a device, make sure it’s on the supported devices list. It sounds simple, but if your particular variation of a device is not supported, the device won’t work. OpenRazer will pick up that it’s a Razer device, but it won’t know how to talk to it. Take my Basilisk Essential, for example. The Basilisk is supported, and I bought the Basilisk Essential thinking it would be the same thing. Big mistake.

Fedora

There is a bug specifically with Fedora that makes it install the wrong kernel headers. To counteract that, install the kernel-devel package before you do anything else by running this command:

sudo

dnf

install

kernel-devel

Hopefully, with the help of OpenRazer, you can get the best out of your Razer peripherals on your Linux system. If your Linux system is running slow, find the cause here. Also, learn how to use the Hosts file to access websites in Linux.

John Perkins

John is a young technical professional with a passion for educating users on the best ways to use their technology. He holds technical certifications covering topics ranging from computer hardware to cybersecurity to Linux system administration.

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How To Find The Length Of Sequence Vector In R?

A sequence vector is created by using the sequence of numbers such as 1 to 15, 21 to 51, 101 to 150, -5 to 10. The length of this type of vectors can be found only by using the length function.

For example, if we have a sequence vector say X then the length of X can be found by using the command given below −

length(X) Example 1

To find the length of sequence vector in R, use the code given below −

x1<-c(1:51,57:200,201:213) x1 Output

If you execute the above given code, it generates the following output −

[1] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 [19] 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 [37] 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 57 58 59 [55] 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 [73] 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 [91] 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 [109] 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 [127] 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 [145] 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 [163] 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 [181] 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 [199] 204 205 206 207 208 209 210 211 212 213

To find the length of sequence vector in R, add the following code to the above code −

x1<-c(1:51,57:200,201:213) length(x1) Output

If you execute all the above given codes as a single program, it generates the following output −

[1] 208 Example 2

To find the length of sequence vector in R, use the code given below −

x2<-c(14:-50,7:48,23:98,21:-10) x2 Output

If you execute the above given code, it generates the following output −

[1] 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 -1 -2 -3 [19] -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14 -15 -16 -17 -18 -19 -20 -21 [37] -22 -23 -24 -25 -26 -27 -28 -29 -30 -31 -32 -33 -34 -35 -36 -37 -38 -39 [55] -40 -41 -42 -43 -44 -45 -46 -47 -48 -49 -50 7 8 9 10 11 12 13 [73] 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 [91] 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 23 [109] 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 [127] 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 [145] 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 [163] 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 [181] 96 97 98 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 [199] 6 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10

To find the length of sequence vector in R, add the following code to the above code −

x2<-c(14:-50,7:48,23:98,21:-10) length(x2) Output

If you execute all the above given codes as a single program, it generates the following output −

[1] 215 Example 3

To find the length of sequence vector in R, use the code given below −

x3<-c(25:-100,1:78,35:-10,40:-5) x3 Output

If you execute the above given code, it generates the following output −

[1] 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 [16] 10 9 8 7 6 5 4 3 2 1 0 -1 -2 -3 -4 [31] -5 -6 -7 -8 -9 -10 -11 -12 -13 -14 -15 -16 -17 -18 -19 [46] -20 -21 -22 -23 -24 -25 -26 -27 -28 -29 -30 -31 -32 -33 -34 [61] -35 -36 -37 -38 -39 -40 -41 -42 -43 -44 -45 -46 -47 -48 -49 [76] -50 -51 -52 -53 -54 -55 -56 -57 -58 -59 -60 -61 -62 -63 -64 [91] -65 -66 -67 -68 -69 -70 -71 -72 -73 -74 -75 -76 -77 -78 -79 [106] -80 -81 -82 -83 -84 -85 -86 -87 -88 -89 -90 -91 -92 -93 -94 [121] -95 -96 -97 -98 -99 -100 1 2 3 4 5 6 7 8 9 [136] 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 [151] 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 [166] 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 [181] 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 [196] 70 71 72 73 74 75 76 77 78 35 34 33 32 31 30 [211] 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 [226] 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 [241] -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 40 39 38 37 36 [256] 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 [271] 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 [286] 5 4 3 2 1 0 -1 -2 -3 -4 -5

To find the length of sequence vector in R, add the following code to the above code −

x3<-c(25:-100,1:78,35:-10,40:-5) length(x3) Output

If you execute all the above given codes as a single program, it generates the following output −

[1] 296 Example 4

To find the length of sequence vector in R, use the code given below −

x4<-c(-50:25,5:61,69:151) x4 Output

If you execute the above given code, it generates the following output −

[1] -50 -49 -48 -47 -46 -45 -44 -43 -42 -41 -40 -39 -38 -37 -36 -35 -34 -33 [19] -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 [37] -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 [55] 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 [73] 22 23 24 25 5 6 7 8 9 10 11 12 13 14 15 16 17 18 [91] 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 [109] 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 [127] 55 56 57 58 59 60 61 69 70 71 72 73 74 75 76 77 78 79 [145] 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 [163] 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 [181] 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 [199] 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151

To find the length of sequence vector in R, add the following code to the above code −

x4<-c(-50:25,5:61,69:151) length(x4) Output

If you execute all the above given codes as a single program, it generates the following output −

[1] 216 Example 5

To find the length of sequence vector in R, use the code given below −

x5<-c(-5:100,9:79,21:-21) x5 Output

If you execute the above given code, it generates the following output −

[1] -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 [19] 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 [37] 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 [55] 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 [73] 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 [91] 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 9 10 [109] 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 [127] 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 [145] 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 [163] 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 21 20 19 [181] 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 [199] 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14 -15 -16 -17 [217] -18 -19 -20 -21

To find the length of sequence vector in R, add the following code to the above code −

x5<-c(-5:100,9:79,21:-21) length(x5) Output

If you execute all the above given codes as a single program, it generates the following output −

[1] 220

Preventing Bash Fork Bombs In Linux

Introduction

Bash Fork Bomb is a type of denial of service (DoS) attack that can crash or freeze a Linux system by overwhelming its resources. attack uses a malicious script that creates a large number of child processes, causing system to run out of available resources, such as memory or CPU time. These child processes then spawn more child processes, and cycle continues until system is unable to respond.

Preventing Bash Fork Bombs in Linux is essential for system administrators to ensure stability and availability of their systems. In this article, we will explore what a Bash Fork Bomb is, how it works, and some methods to prevent it.

What is a Bash Fork Bomb?

A Bash Fork Bomb is a type of denial-of-service (DoS) attack that exploits fork() system call in Linux. Fork() is used to create a new process by duplicating calling process. A Bash Fork Bomb is created by a malicious script that recursively calls itself, creating a large number of child processes. child processes then call themselves, and cycle continues, creating an exponential growth of processes until system crashes or freezes.

Here’s an example of a Bash Fork Bomb −

This is a one-liner command that recursively calls a function named “:”. function pipes its output to another call of same function, and ampersand (&) sends process to background. This creates a child process that is then duplicated and creates another child process, and cycle continues until system crashes or freezes.

How does a Bash Fork Bomb Work?

A Bash Fork Bomb works by recursively calling a function that creates child processes. Each child process creates more child processes, and cycle continues until system runs out of available resources. When a new process is created using fork(), it duplicates parent process, including its memory and file descriptors. new process is then independent of parent process and can execute its own code. This allows Bash Fork Bomb to create an exponential growth of child processes, overwhelming system’s resources.

Preventing Bash Fork Bombs in Linux

There are several methods to prevent Bash Fork Bombs in Linux. These methods involve limiting number of processes, setting resource limits, and configuring system settings.

Limit number of processes − One way to prevent Bash Fork Bombs is to limit number of processes that can be created. This can be done by setting a maximum number of processes that can be created per user or system-wide. maximum number of processes can be set using ulimit command.

To set a maximum number of processes for a user, use following command −

To set a maximum number of processes system-wide, edit chúng tôi file and add following lines −

Set resource limits − Another way to prevent Bash Fork Bombs is to set resource limits for processes. Resource limits define maximum amount of resources that a process can use, such as CPU time, memory, and disk space. These limits can be set using ulimit command or by editing chúng tôi file.

To set a maximum amount of CPU time for a process, use following command −

To set a maximum amount of memory for a process, use following command −

To set a maximum amount of disk space for a process, use following command −

To set resource limits system-wide, edit chúng tôi file and add following lines −

Configure system settings − Linux has several system settings that can be configured to prevent Bash Fork Bombs. These settings include setting a maximum number of processes, maximum amount of memory, and maximum amount of CPU time that can be used by all processes.

To set a maximum number of processes system-wide, edit chúng tôi file and add following line −

To set a maximum amount of memory system-wide, edit chúng tôi file and add following line −

To set a maximum amount of CPU time system-wide, edit chúng tôi file and add following line −

Additional Methods for Preventing Bash Fork Bombs in Linux

Use Process Accounting − Process accounting is a Linux feature that tracks system resources used by each process. By using process accounting, system administrators can monitor and limit resources used by each process, which can help prevent Bash Fork Bombs.

To enable process accounting, use following command −

sudo apt-get install acct

Once installed, process accounting can be enabled by adding following line to /etc/default/acct file −

ENABLE_ACCT=1

Use cgroups − Control Groups (cgroups) is a Linux feature that allows system administrator to limit resources used by processes. Cgroups provide a more fine-grained approach to resource management than methods described above. By using cgroups, system administrators can set limits on CPU usage, memory usage, and other system resources.

To use cgroups, install cgroup-tools package using following command −

sudo apt-get install cgroup-tools

Once installed, cgroups can be configured by creating a configuration file in /etc/cgconfig.d directory. For example, to limit CPU usage of all processes in user group “webapps” to 50%, create a configuration file named “webapps.conf” with following content −

group webapps { cpu { cpu.shares = 512; } }

Use a process supervisor − A process supervisor is a program that manages and monitors execution of other programs. By using a process supervisor, system administrators can limit number of processes that can be created and monitor resource usage of each process. Some popular process supervisors for Linux include systemd, Upstart, and supervisord.

Conclusion

Bash Fork Bombs are a serious threat to stability and availability of Linux systems. Preventing Bash Fork Bombs in Linux is essential for system administrators to ensure smooth operation of their systems. Limiting number of processes, setting resource limits, and configuring system settings are some methods to prevent Bash Fork Bombs. By implementing these methods, system administrators can protect their systems from this type of denial-of-service attack.

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