Some implementations of dd will print progress information when they receive SIGINFO (a non-standard signal not supported on all platforms). Check your documentation and/or run a test with another dd (perhaps reading from a neverending file to an unfillable sink):

Code:

dd if=/dev/zero of=/dev/null bs=1

From another terminal, grab the pid (make sure it's the correct instance of dd), and send the signal.

Code:

kill -INFO pid

If dd prints progress info without dying, then you can use it safely on your long-running dd.

Or, if you're the daring sort, just kill your long-running dd with kill -INT pid. Before exiting, it will print the number of bytes written. You can then resume with the larger blocksize suggested by Scrutinizer, using the skip and seek operands (you'll have to do a little arithmetic to figure out how many complete new-size blocks were written and need to be skipped in both the source and target).

If the blocksize uses a suffix (in 1M, that would be the letter M), be very careful to use the correct multiplier. M is usually 2^20 bytes (1,048,576), not 10^6 (1,000,000). Similar traps await at other magnitudes (kilo, giga).

Are you feelin' lucky?

Regards,
Alister

---------- Post updated at 02:00 PM ---------- Previous update was at 01:51 PM ----------

I don't use Linux much, but that's good to know. Thanks. If the system supports it, it responds to SIGINFO as well (which is the signal used by *BSD dd).

Probably the wisest choice for now.

Regards,
Alister