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

Shell Programming and Scripting
1

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:

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:

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

2

Why not just read/write the first 1MB from file(randomfile.txt) to another file:

head -c1MB randomfile.txt > test.txt
3

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.

while true
do
        cat inputfile
done | dd bs=1024 count=1024 > outputfile
4

Could you use openssl to generate your random file directly, e.g. for 1Mb file use:

$ openssl rand 1048576 > myfile.fifo
1 Like
5

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

6

How about just using dd to append to file each time:

$ 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

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...

dd if=mynamed.fifo of=myfile.fifo bs=1048576 count=1
8

Hey Guy's,

I haven't tried the conv= or the oflag= . I'll give these a spin and see how they work. Need to first check if they're universally available. Tried seek= and count= as well. That seemed to do the job.

Cheers,
DH