You can use
shred for files or partitions/hard drives:
sudo if required to gain administrative privileges.
For a partition:
shred -vfz -n 10 /dev/sdXZ
For a drive:
shred -vfz -n 10 /dev/sdX
Note! Substitute "X" and "Z" with the adequate number or letter for partition/drive
For a file:
shred -v -u -n 2 -z moo.txt
$ shred -v -u -n 2 -z moo.txt
shred: moo.txt: pass 1/3 (random)...
shred: moo.txt: pass 2/3 (random)...
shred: moo.txt: pass 3/3 (000000)...
shred: moo.txt: removing
shred: moo.txt: renamed to 0000000
shred: 0000000: renamed to 000000
shred: 000000: renamed to 00000
shred: 00000: renamed to 0000
shred: 0000: renamed to 000
shred: 000: renamed to 00
shred: 00: renamed to 0
shred: moo.txt: removed
-f, --force change permissions to allow writing if necessary
-n, --iterations=N overwrite N times instead of the default (3)
--random-source=FILE get random bytes from FILE
-s, --size=N shred this many bytes (suffixes like K, M, G accepted)
-u, --remove truncate and remove file after overwriting
-v, --verbose show progress
-x, --exact do not round file sizes up to the next full block;
this is the default for non-regular files
-z, --zero add a final overwrite with zeros to hide shredding
--help display this help and exit
--version output version information and exit
If FILE is -, shred standard output.