(most probably) OT: /dev/random and /dev/urandom

[Michele Dondi]

I apologize in advance for posting this question that I feel is most
probably OT (if it actually is OT). I have this small script:

#!/usr/bin/perl

use strict;
use warnings;

$/=\0x100_000;
open my $fh, '<:raw', '/dev/urandom' or die $!;
print scalar <$fh>;

__END__

If I run it I get:

# ./foo.pl | wc -c
1048576
# ./foo.pl | wc -c
1048576
# ./foo.pl | wc -c
1048576
# ./foo.pl | wc -c
1048576

[ad libitum]

If I change /dev/urandom to /dev/random, then I get:

# ./foo.pl | wc -c
89
# ./foo.pl | wc -c
89
# ./foo.pl | wc -c
89
# ./foo.pl | wc -c
82
# ./foo.pl | wc -c
^[[A

["hangs", had to press CTRL-C]

FWIW I'm running a 2.6.3 kernel. May something be wrong with my system
or am I doing this *in perl* the wrong way?!?


TIA,
Michele

 

[Anno Siegel]

I apologize in advance for posting this question that I feel is most
probably OT (if it actually is OT). I have this small script:

#!/usr/bin/perl

use strict;
use warnings;

$/=\0x100_000;
open my $fh, '<:raw', '/dev/urandom' or die $!;
print scalar <$fh>;

__END__

If I run it I get:

# ./foo.pl | wc -c
1048576

....as expected.

[...]

If I change /dev/urandom to /dev/random, then I get:

# ./foo.pl | wc -c
89

That behavior is wrong. The only difference in /dev/urandom and /dev/random
is that random may block when it runs out of entropy while urandom continues
to deliver random data of lower quality. Stick to urandom until the other
can be repaired.

Anno