You can dod alogos of scub command to wipe disk securely on Linux / Unix system. The syntax is as follows to wipe a /dev/sda (warning be careful with device name. Always keep backups. Data once wiped can not be recovered):
# scrub -p dod /dev/sda
scrub: using DoD 5220.22-M patterns scrub: please verify that device size below is correct! scrub: scrubbing /dev/sda 399717171200 bytes (~372GB) scrub: random |........