If you don’t want or can’t use shred, it’s possible to use dd to erase the content of a partition.
Quick and unsafe method
The first method is to write 0 on all sectors of the disk in a single pass:
# dd if=/dev/zero of=/dev/sdX bs=512 conv=notruncSlow and moderately safe method
The second method, a bit more secure than the previous one, is to fill sector with data from the kernel pseudorandom number generator:
# dd if=/dev/urandom of=/dev/sdX bs=512 conv=notruncSlow and safe method
Pretty much the same method then the previous one, but this time we will make multiple pass (here 8) :
# for n in `seq 8`; do dd if=/dev/urandom of=/dev/sdX bs=512 conv=notrunc; done