Надежно удалить файл в Ubuntu?

Thanks to @GZBK for pointing me to the wipe package.

For future readers in this thread, I want to quote several parts of wipe's man page.

Journaling filesystems (such as Ext3 or ReiserFS) are now being used by default by most Linux distributions. No secure deletion program that does filesystem-level calls can sanitize files on such filesystems, because sensitive data and metadata can be written to the journal, which cannot be readily accessed. Per-file secure deletion is better implemented in the operating system.

So if you're using a journaled fie system, then any 3rd party secure deletion program will not be as secure as you may be lead to believe. Kernel-level secure deletion routines have more direct access to the disk and may be able to bypass some of these limitations. But even for kernels...

Be aware that harddisks are quite intelligent beasts those days. They transparently remap defective blocks. This means that the disk can keep an albeit corrupted (maybe slightly) but inaccessible and unerasable copy of some of your data. Modern disks are said to have about 100% transparent remapping capacity. You can have a look at recent discussions on Slashdot.

I hereby speculate that harddisks can use the spare remapping area to secretly make copies of your data. Rising totalitarianism makes this almost a certitude. It is quite straightforward to implement some simple filtering schemes that would copy potentially interesting data. Better, a harddisk can probably detect that a given file is being wiped, and silently make a copy of it, while wiping the original as instructed.

So if you are handling highly sensitive information then you should treat the hardware of your hard disk as malicious, and only pass data to the disk in fully encrypted form by using full disk encryption in the OS. Furthermore, when discarding a drive with sensitive data on it, you should ensure that it has been properly physically destroyed (many companies offer hard drive shredding services) rather than relying on software wipes.

Update

As pointed out by GZBK in comments below, this information appears to be out of date. In particular, it appears that the man page for wipe hasn't been updated since 2006.