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Need to generate a file with random data. /dev/[u]random doesn't exist.


 
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Top Forums Shell Programming and Scripting Need to generate a file with random data. /dev/[u]random doesn't exist.
# 1  
Old 08-16-2013
Need to generate a file with random data. /dev/[u]random doesn't exist.

Need to use dd to generate a large file from a sample file of random data. This is because I don't have /dev/urandom.

I create a named pipe then:

Code:
dd if=mynamed.fifo do=myfile.fifo bs=1024 count=1024

but when I cat a file to the fifo that's 1024 random bytes:

Code:
cat randomfile.txt > mynamed.fifo;

the dd command exits writing only 1024 (Likely the EOF thing). so I never get my 1MB file. How do I get around this? How do I ensure it generates the random data file without closing dd? Is there something else I need to pass?

Cheers,
DH

Last edited by Scott; 08-16-2013 at 01:05 PM.. Reason: Code tags, please.
# 2  
Old 08-16-2013
Why not just read/write the first 1MB from file(randomfile.txt) to another file:
Code:
head -c1MB randomfile.txt > test.txt

# 3  
Old 08-16-2013
What system doesn't have /dev/urandom? What languages do you have available?

How about this? When dd quits, it should kill the while-loop too. No named pipe needed.

Code:
while true
do
        cat inputfile
done | dd bs=1024 count=1024 > outputfile

# 4  
Old 08-19-2013
Could you use openssl to generate your random file directly, e.g. for 1Mb file use:

Code:
$ openssl rand 1048576 > myfile.fifo

This User Gave Thanks to Chubler_XL For This Post:
# 5  
Old 08-22-2013
Thanks very much all for the replies. Really appreciate it. The place to run this for me would be even in basic shells like the Linux, Solaris, AIX etc 'maintenance' / 'recovery' shells.

So things like Perl or openssl won't work as required libraries won't be loaded in those simple recovery shells.

Corona688:
That's a good option there but unfortunately it didn't work fully or I should say it DID work partially. The loop continued to run even though the dd command ended / stopped.

Cheers,
DH

Last edited by Devyn; 08-22-2013 at 06:49 PM..
# 6  
Old 08-22-2013
How about just using dd to append to file each time:

Code:
$ dd if=randomfile1.txt of=myfile.fifo oflag=append conv=notrunc
$ dd if=randomfile2.txt of=myfile.fifo oflag=append conv=notrunc
$ dd if=randomfile1.txt of=myfile.fifo oflag=append conv=notrunc

# 7  
Old 08-22-2013
Thinking laterally, a long shot, but worth a try...

Not sure why you need to use 1024 for block size, but my dd command will accept a bs of 1048576 so...
Code:
dd if=mynamed.fifo of=myfile.fifo bs=1048576 count=1


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