Badblocks: non-destructive read-write mode

With the -n flag ("non-destructive read-write mode"), badblocks does the following sequence in every iteration:

1. read data
2. write test pattern (test pattern is ~0 (0xffff in 32-bit int))
3. read test pattern
4. compare test pattern
5. write data

It will try to write back the original data when terminated with the following signals:

• SIGHUP
• SIGINT
• SIGPIPE
• SIGTERM
• SIGUSR1
• SIGUSR2

Killing it with SIGKILL is dangerous because you have, at best, 3/4 chance of corrupting your disk (the only safe state to SIGKILL is when it does read data).