UNIX random devices and utilities

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23
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2answers
13k views

How can I populate a file with random data?

How can I create a new file and fill it with 1 Gigabyte worth of random data? I need this to test some software. I would prefer to use /dev/random or /dev/urandom.
19
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4answers
6k views

Why does dd from /dev/random give different file sizes?

I am running the following command on an ubuntu system: dd if=/dev/random of=rand bs=1K count=2 However, every time I run it, I end up with a file of a different size. Why is this? How can I ...
17
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3answers
1k views

Run commands at random

I want to run one of the two commands C1 and C2 at random. How do I do that on commandline (bash)? Will appreciate if a one-liner is possible.
16
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2answers
1k views

Why writing to /dev/random does not make parallel reading from /dev/random faster?

Typically reading from /dev/random produces 100-500 bytes and blocks, waiting for an entropy to be collected. Why doesn't writing information to /dev/random by other processes speed up reading? ...
11
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4answers
6k views

Why can't tr read from /dev/urandom on OSX?

A colleague suggested creating a random key via the following command: tr -dc A-Za-z0-9_\!\@\#\$\%\^\&\*\(\)-+= < /dev/urandom | head -c 32 | xargs It gave me the error: tr: Illegal byte ...
11
votes
4answers
806 views

Shuffle file randomly with some additional constraints

I have a huge music playlist and, while some artists have many albums, others have just one song. I wanted to sort the playlist so the same artist won't play twice in a row, or his songs won't end up ...
11
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4answers
3k views

Tool for measuring entropy quality?

Is there a tool available for Linux systems that can measure the "quality" of entropy on the system? I know how to count the entropy: cat /proc/sys/kernel/random/entropy_avail And I know that some ...
10
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3answers
7k views

Reading from /dev/random does not produce any data

I often use the command cat /dev/urandom | strings --bytes 1 | tr -d '\n\t ' | head --bytes 32 to generate pseudo-random passwords. This doesn't work with /dev/random. Specifically cat ...
9
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4answers
13k views

Generate random numbers in specific range

After googling a bit I couldn't find a simple way to generate with a shell command a random number included in a specific range, between a minimum and a maximum. I read about /dev/random, ...
8
votes
1answer
3k views

Writing /dev/random to file?

If you ran the following, what would happen? cat /dev/random > ~/randomFile # don't run Would it be written until the drive runs out of space, or would the system see a problem with this and ...
8
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2answers
2k views

Adding “random number entropy” for GPG keys?

In the following video: Linux HOWTO: Secure Your Data with PGP, Part 2, you are shown how to create a key pair with gpg. At about 1:50, the instructor says the following: While the key is being ...
7
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1answer
1k views

Is /dev/random data a psuedo-random AES cypher, and where does the entropy come from?

My current understanding of an entropy pool is that it gathers truly random bits of data at a slow rate. I'd like to know how Unix & Linux collect entropy, and how that entropy is used by ...
7
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2answers
2k views

RSA 2048 keypair generation: via openssl 0.5s via gpg 30s, why the difference?

RSA 2048 keypair generation: via openssl 0.5s via gpg 30s, why the difference There are several programs which can gerate RSA public/private keypairs GnuPG/OpenPGP for instance has a wizzard being ...
7
votes
3answers
913 views

Lightweight utility/program to run a command after a random delay

I need to randomize the time before a given command starts. I realize it's relatively trivial to do this within a script, or to write a "wrapper" script to do this, but I'm wondering if anyone knows a ...
7
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2answers
2k views

Create random data with dd and get “partial read warning”. Is the data after the warning now really random?

I create a 1TB file with random data with dd if=/dev/urandom of=file bs=1M count=1000000. Now I check with kill -SIGUSR1 <PID> the progress and get the following: 691581+0 Datensätze ein ...
7
votes
1answer
174 views

/usr/bin/random using a lot of CPU

Using QNX 6.4.1, there is a command called pidin times that shows information about processes. I think it means PID INformation. Among other things, you can see how much CPU a process has used since ...
6
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2answers
3k views

dd if=/dev/random is 'randomly' bottlenecked with BIG time lags, but I have no idea why

I get wildly different real times when I run the following command. dd if=/dev/random bs=1k count=1 It doesn' happen for if=/dev/null, nor does it happen for if=/dev/urandom I've run it 500 ...
6
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2answers
1k views

What keeps draining entropy?

If I do watch cat /proc/sys/kernel/random/entropy_avail I see that my systems entropy slowly increases over time, until it reaches the 180-190 range at which point it drops down to around 120-130. The ...
6
votes
1answer
250 views

Can you explain the entropy estimate used in random.c

/dev/random uses the timings of kernel interupts to add to the entropy pool. The amount of entropy in the pool is tracked in a variable named entropy_count. Here is the relevant snippet of code from ...
5
votes
5answers
588 views

Sources of Entropy for Linux

Let's say I want a gigabyte or so of random data from /dev/random, suitable for a one-time pad (so /dev/urandom is out.) How do I seed my /dev/random with enough entropy to do this? I am looking for ...
5
votes
1answer
385 views

How to copy a file several times into randomly choosen paths within the filesystem?

I have a filesystem and a special file foo. I would like the script to choose several times (5,10 or 100) random paths to folders within this filesystem and to copy the file foo into each of them. ...
5
votes
1answer
74 views

What does this command actually cause?

Once while talking with my friend I was trying to joke that we might stand a better chance of completing our project if we just run loads of random programs and expect one of them to solve our ...
5
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2answers
535 views

How to determine which processes are using how much entropy from /dev/urandom

Doing fuser -v /dev/urandom tells me which processes currently have /dev/urandom open, but only that. Is there any was to determine anything about how much entropy each one is using up over time? ...
4
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2answers
405 views

random permutation of lines of text

If I have a file with following content: 0001 0002 0003 0004 0132 0137 0138 0141 How can I get a random permutation of them in bash?
4
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4answers
430 views

How to fill a file with a stream from /dev/urandom with a specified number of lines ?

I am trying to fill a file with a sequence of random 0 and 1s with a user-defined number of lines and number of characters per line. the first step is to get a random stream of 0 and 1s: cat ...
4
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2answers
261 views

Generating file with ASCII numbers using /dev/urandom?

How can I generate 10 MB files from /dev/urandom filled with: ASCII 1s and 0s ASCII numbers between 0 and 9
4
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5answers
4k views

Fast Way to Randomize HD?

I've read about how to make hard drives secure for encryption, and one of the steps is to write random bits to the drive, in order to make the encrypted data indistinguishable from the rest of the ...
4
votes
1answer
206 views

measure amount of data read from /dev/random

background I have written a collection of bash scripts (most of them in German only yet but if you are interested; download the archive not the single scripts) which help users create high-quality ...
3
votes
2answers
107 views

How to quickly generate (insecure) GPG keys?

I'd like to automate generating at least two GPG keys for testing and demonstration purposes in a virtual machine. Because of this context I want to make sure the key generation is fast, ideally not ...
3
votes
2answers
37 views

Decreasing or emptying the entropy pool?

I work with virtual machines a lot, and they seem to generally be low on entropy (no mouse or other entropy-generating inputs). A bug with my software has surfaced, and I think it's due to running out ...
3
votes
2answers
440 views

Why doesn't `head -c 2 /dev/hwrng` work?

I have an Atmel 97SC3201 in my computer and set the following in the kernel: CONFIG_HW_RANDOM_TPM CONFIG_TCG_TPM CONFIG_TCG_ATMEL /dev has tpm0 and hwrng, but running this command returns the ...
3
votes
1answer
721 views

How to debug random reboots, with no kernel panic, of an embedded system?

I have two aValue RPC-10W1 embedded systems that reboots by themselves after 1-2 hours. Facts: The board will reboot within a time span of 1 to 2½ hours. The issue is present on two identical ...
3
votes
1answer
525 views

Debian Jessie - Random freezes

I have a fresh installation of Debian Jessie, with Cinnamon and Gnome. I run it on a decent computer with the following specs: Athlon II x3, 6GB DDR2, 2GB SWAP (swapiness minimum), 600GB SATA HDD ...
3
votes
1answer
40 views

How random is the pseudo random number generators on live boot disks? Is there a way to seed it?

I know that random number generators on computers are only pseudo-random, but are the PRNGs on Live Boot USB or DVDs even less random? Is there a way to seed them after booting? Specifically curious ...
2
votes
2answers
136 views

How to generate a random string in a profile alias?

I have an alias in my server's /etc/profile which generates a random directory on command, like this: alias rdir="mkdir -p ./`cat /dev/random | tr -cd 'a-z0-9' | head -c 8`/" But it turns out this ...
2
votes
2answers
60 views

How can I shuffle pages from a pdf file in a random order?

I would like to shuffle the pages of a pdf document in a random order. How can this be done?
2
votes
4answers
450 views

Overwriting a Disk

Should I use: find / -type f -exec shred -uvz -nX or just good old dd if=/dev/urandom of=/dev/sda Is one faster or more secure than the other?
2
votes
1answer
555 views

Use the raspberry pi as a source of entropy for /dev/random

I'm trying to see if I can use my raspberry pi's hardware RNG as a source of entropy for /dev/random. Mostly to see if I can get it to work and find yet another use for this nifty little device. Of ...
2
votes
2answers
198 views

Feeding /dev/random with disk reads etc

Is there any way to feed /dev/random with sufficient entropy? The data doesn't have to be truly random, i.e. I can append time of day with pid and add 27 to it, it doesn't matter I just want to make ...
2
votes
1answer
160 views

Low(?) entropy available on Arch Linux?

I just had some problems to get Pidgin with OTR running, because Pidgin hung on every attempt to generate my private key. This rather old blog post pointed me into the right direction (or rather ...
2
votes
1answer
313 views

rngd - multiple instances from init script

On Ubuntu >=12.04, what is the most correct/prettiest way to get rngd to run in multiple instances using an init script? The current one only accepts one random source, so multiple instances are ...
2
votes
3answers
105 views

gpg key generation on Tails live cd - why so quick?

I just used gpg2 --gen-key to generate a 2048 bit RSA key pair on an OS running on a live cd (Tails). This happened much faster than I expected. When I have done this before on a regular machine it ...
2
votes
1answer
342 views

Changing the hostname on a Linux Mint desktop to a random value at boot time

When changing the hostname to a random set of alphanumeric characters on a machine running Linux Mint(17.1 Rebecca, Cinnamon 64-bit) I encounter some problems. The following script changes the ...
2
votes
1answer
98 views

What entropy sources are used by the Linux kernel?

man 4 random has a very vague description of Linux kernel entropy sources: The random number generator gathers environmental noise from device drivers and other sources into an entropy ...
2
votes
1answer
59 views

What is the correct available entropy on UNIX systems?

I have three questions related to entropy on UNIX systems: I check entropy on Linux using: cat /proc/sys/kernel/random/entropy_avail. Is this the standard place with information about available ...
1
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2answers
1k views

random number needed

I need a command line script that will generate a random integer between 1 and 6. I'm using Ubuntu with bash. I was working on this a couple of months ago using 'bc', but never got it to work ...
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3answers
1k views

How can I randomize file names in a given directory?

Ok, this may sound like an odd request but it really has a good purpose! I have a Panasonic Plasma TV with an SD card slot, via which I can display a slideshow of JPEG photos. This is useful for ...
1
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2answers
25 views

Randomly copy certain amount of certain file type from one directory into another

Sometimes I have a folder full of jpg's and I need to randomly choose 8 or so of them. How could I automate this so my account randomly chooses 8 jpg's from the folder and copies them to another ...
1
vote
2answers
47 views

Creating a device similar to /dev/random from a script

I am writing a program for which I will create a script to generate test data in a specific format. How can I create a /dev/myprogram device that would work similar to /dev/random (preferably in ...
1
vote
2answers
100 views

Randomize arguments ( that hold color codes) from an array

I have the array (shown below) with arguments that hold color codes. The intended purpose of my script is to randomize those arguments when the user inputs "scriptname randoms Text" so that every time ...