I recently upgraded Firefox to the latest build.

Then, my geckodriver binary stopped working in Python.

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firefox --version

Mozilla Firefox 71.0



python --version

Python 3.8.0



/bin/geckodriver --version

geckodriver 0.24.0

The main problem, I had an outdated Geckodriver version (from the distro repo)

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sudo pacman -R geckodriver

/bin/geckodriver --version

bash: /bin/geckodriver: No such file or directory

Find the latest version

https://github.com/mozilla/geckodriver/releases/

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cd /opt

sudo wget https://github.com/mozilla/geckodriver/releases/download/v0.26.0/geckodriver-v0.26.0-linux64.tar.gz



sudo tar -xzvf geckodriver.tar.gz && rm -f geckodriver.tar.gz



sudo chmod +x geckodriver



sudo chmod 755 geckodriver



sudo cp geckodriver /bin/geckodriver

Geckordriver should be updated to the latest version:

geckodriver --version
geckodriver 0.26.0

Docker doesn’t come with “stock” repos on CentOS, some variations of alias programs are installations like podman.

These lack many of the core commands of the “real” Docker.

Here is a guide to install Docker Latest Version on CentOS.

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yum clean all -y

yum update -y

yum upgrade -y



dnf config-manager --add-repo=https://download.docker.com/linux/centos/docker-ce.repo



DOCKERVERSION=$(dnf list docker-ce --showduplicates | \

sort -r | \

grep "docker-ce.x86_64" -m1 | \

sed -e 's/docker\-ce\.x86\_64//g' -e 's/docker\-ce\-stable//g' | \

tr -d [:space:])



echo "Installing docker-ce-$DOCKERVERSION"



# remove this line in auto environments

read -p "Does this look right? Ctrl C to stop."



dnf install containerd -y



dnf install docker-ce-$DOCKERVERSION -y



# if the above fails, try the latest compatible via

dnf --nobest install docker-ce-$DOCKERVERSION --nobest -y

As we all know, the shell builtin variable $RANDOM is a pseudo random number generator.

Today, we will be looking at some creative ways to generate psuedo random numbers, trying to use shell builtins as much as possible.

The Best Solution is shuf (not exactly builtin though)

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# Shuffle and return n'th line of range

shuf --head-count="1" --input-range="1-10000"

shuf -n1 -i1-10000

9523

Ways to generate various strings of numbers in BASH

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# Generate a number between 0 - 32767

echo $RANDOM

7469

$RANDOM Caveats

From the 2 above scenarios, we analyse the distribution of the digits and find out the frequency of each value in order to see how random they really are:

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# Count the frequency of numbers in a 10000 samples

# cut -c1 chops the first digit from our variable



for i in $(seq 1 1000); do

    RNUMS+=($(cut -c1 <<< $RANDOM))

done



### OR



while [[ $COUNTER -le 1000 ]]; do

     RNUMS+=($(cut -c1 <<< $RANDOM))

     COUNTER=$COUNTER+1

done



# show RNUMS array length, should be 1000

echo ${#RNUMS[@]}

Now, we want to test the frequency of each digit:

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for n in ${RNUMS[@]}; do

    case $n in

        1 ) ((ones++))

            ;;

        2 ) ((twos++))

            ;;

        3 ) ((three++))

            ;;

        4 ) ((fours++))

            ;;

        5 ) ((fives++))

            ;;

        6 ) ((sixes++))

            ;;

        7 ) ((sevens++))

            ;;

        8 ) ((eights++))

            ;;

        9 ) ((nines++))

            ;;

        0 ) ((zeros++))

            ;;

    esac

done



echo $ones $twos $threes $fours $fives $sixes $sevens $eights $nines $zeros

Strangely, the output expected should be ~100, ~100, ~100…

However, the output is totally different:

330 367 108 22 41 28 30 42 33

Creative Ways To Generate Bad Random Numbers In Bash

The second digit from $RANDOM$RANDOM

cut -c2 <<< $RANDOM$RANDOM

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# cut the 2nd digit from RANDOMRANDOM

# $RANDOM's minimum value is 1 therefore the second digit should always be there

# Do not use this value on its own though, as it clearly is not random

while [[ $COUNTER -le 1000 ]]; do

     RNUMS+=($(cut -c2 <<< $RANDOM$RANDOM))

     COUNTER=$COUNTER+1

done

# frequency test

111 114 92 97 86 87 89 95 105 125



# again

120 100 108 93 100 97 78 83 97 125



# CLEARLY NOT RANDOM

A digit from $(date +%N)

cut -c9 <<< $(date +%N)

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# Print the time in nanoseconds of the current moment

# Do not use this value on its own though, as it clearly is not random

date +%N

277936336

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while [[ $COUNTER -le 1000 ]]; do

     RNUMS+=($(cut -c9 <<< $(date +%N)))

     COUNTER=$COUNTER+1

done

# frequency test

103 89 105 92 102 104 100 106 91 109

# DECENTLY RANDOM

A digit from cksum <<< $RANDOM$RANDOM

cut -c2 <<< $(cksum <<< $RANDOM$RANDOM)

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# Checksum $RANDOM$RANDOM

echo $(cksum <<< $RANDOM$RANDOM)

277936336

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while [[ $COUNTER -le 1000 ]]; do

     RNUMS+=($(cut -c2 <<< $(cksum <<< $RANDOM$RANDOM)))

     COUNTER=$COUNTER+1

done

# frequency test

128 123 91 78 101 95 85 86 92 122

# again

124 111 110 79 82 91 100 103 84 117

# and again

126 118 104 92 101 85 88 87 86 114

# CLEARLY NOT RANDOM!

A digit from cksum <<< $(($RANDOM*$RANDOM))

cut -c2 <<< $(cksum <<< $(($RANDOM*$RANDOM)))

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# Checksum $RANDOM x $RANDOM

while [[ $COUNTER -le 1000 ]]; do

     RNUMS+=($(cut -c2 <<< $(cksum <<< $(($RANDOM*$RANDOM)))))

     COUNTER=$COUNTER+1

done

# and analysis

112 127 107 103 88 84 106 85 81 108

126 106 97 99 85 99 88 83 105 113

# CLEARY NOT RANDOM!

Shuf 1-10

shuf -n1 -i1-10

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# Shuffle 1-10

while [[ $COUNTER -le 1000 ]]; do

     RNUMS+=($(shuf -n1 -i1-10))

     COUNTER=$COUNTER+1

done

# and analysis

95 107 76 93 113 88 116 109 110

101 95 116 100 107 109 83 91 103

# GREAT RANDOM NUMBER GENERATOR

The Fibonacci sequence is a mathematical sequence of numbers such that the result is the sum of the previous two numbers in the sequence starting at x=0 and y=1. Hence,

z = x + y

We can write a script to calculate this function in bash or shell commands.

First, I needed to visualize the idea:

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x + y = z

z + y = z2

To help us figure this out we need to see what happens after the first iteration to work out how to change our variables and then send them through a loop.

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x=0

y=1

z=0

# first time

z=$(( x + y ))

echo $z

Output~:$ 1

After the first time the sequence happens we need to add “x and y” again. On the second run z should be increased too. So how do we assign them?

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# when we add x + y, then z became 1

# but now we need to to be replace y and then x for the second run.

# We can build a small tree to see what's happening



x   y   z

0 + 1 = 1

1 + 1 = 2

1 + 2 = 3

2 + 3 = 5

3 + 5 = 8

5 + 8 = 13

8 + 13= 21



# the z comes from nowhere else but the result of what we are about to do

# but we now know what we need to use in the second run, third run, and so on.

# We should make x now become y

x=$y



# and then y become z! $y needs to be give its value to x right

# before we give $y a new value from $z

y=$z

Now, how do we loop it? We can use a while loop. This while loop simply checks if $x is true. Whenever $x has a value, it will run. Hence, it will run forever.

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y=1

while true; do

  let z=x+y

  echo $z

  x=$y

  y=$z

done

Here’s the result:

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[[email protected] ~]$ y=1

[[email protected] ~]$ while true; do

>   let z=x+y

>   echo $z

>   x=$y

>   y=$z

> done

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34

55

89

144

233

377

610

987

1597

2584

4181

6765

10946

17711

28657

46368

75025

121393

196418

317811

514229

832040

1346269

2178309

3524578

5702887

9227465

14930352

24157817

39088169

63245986

102334155

165580141

267914296

433494437

701408733

1134903170

1836311903

2971215073

4807526976

7778742049

12586269025

20365011074

32951280099

53316291173

86267571272

139583862445

225851433717

365435296162

591286729879

956722026041

1548008755920

2504730781961

4052739537881

6557470319842

10610209857723

17167680177565

27777890035288

44945570212853

72723460248141

117669030460994

190392490709135

308061521170129

498454011879264

806515533049393

1304969544928657

2111485077978050

3416454622906707

5527939700884757

8944394323791464

14472334024676221

23416728348467685

37889062373143906

61305790721611591

99194853094755497

160500643816367088

259695496911122585

420196140727489673

679891637638612258

1100087778366101931

1779979416004714189

2880067194370816120

4660046610375530309

7540113804746346429

-6246583658587674878

1293530146158671551

-4953053512429003327

-3659523366270331776

-8612576878699335103

6174643828739884737

-2437933049959450366

3736710778780434371

1298777728820984005

5035488507601418376

6334266236422402381

-7076989329685730859

-742723093263328478

-7819712422949059337

-8562435516212387815

2064596134548104464

-6497839381664283351

-4433243247116178887

7515661444929089378

3082418197812910491

-7848664430967551747

-4766246233154641256

5831833409587358613

1065587176432717357

6897420586020075970

7963007762452793327

-3586315725236682319

4376692037216111008

790376311979428689

5167068349195539697

5957444661174968386

-7322231063339043533

-1364786402164075147

-8687017465503118680

8394940206042357789

-292077259460760891

8102862946581596898

7810785687120836007

-2533095440007118711

5277690247113717296

2744594807106598585

8022285054220315881

-7679864212382637150

342420841837678731

-7337443370544958419

-6995022528707279688

4114278174457313509

-2880744354249966179

1233533820207347330

-1647210534042618849

-413676713835271519

-2060887247877890368

-2474563961713161887

-4535451209591052255

-7010015171304214142

6901277692814285219

-108737478489928923