Code:
# dd if=/dev/random of=/dev/sd1c &
dd: /dev/random: Input/output error
0+0 records in
0+0 records out
0 bytes transferred in 0.000 secs (0 bytes/sec)
#
But "dd if=/dev/urandom of=/dev/sd1c &" works fine. Is /dev/random not supposed to be used or something?