Run dolphin file manager as root
Some system files are visible in mac finder only when it opened with root privileges.
kdesu dolphin
Change Password Of dmg files
hdiutil chpass <dmg_file_name>
Secure Delete Deleted Files
Warning! It’s critically important that you include the freespace portion of that command. If you don’t, diskutil will happily start securely erasing the entire disk, instead of just the free space!
# diskutil list
diskutil secureErase freespace 1 /dev/disk3s4
Check how fast is your mac write data to its disk
time dd if=/dev/zero bs=1024k of=tstfile count=1024
Secure Delete Files / Folders
srm <file_name>
srm -r <folder_name>