Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and other Un*x-like operating systems. It only takes a minute to sign up.
Sign up to join this community
I am using dd to do a network transfer of a disk image to an sd card on my BeagleBone.
Using pkill -USR1 -n -x dd in an ssh connection to this BeagleBone gives me a status update of the transfer process, which is great. I am just curious how it is actually working so I can use it effectively in the future.
After reading man pkill it still didn't totally explain how pkill -USR1 -n -x dd is working to give me this very useful status update.
This is behavior specific to dd. From the dd man page:
Sending a USR1 signal to a running 'dd' process makes it print I/O statistics to standard error and then resume copying.
$ dd if=/dev/zero of=/dev/null& pid=$! $ kill -USR1 $pid; sleep 1; kill $pid 18335302+0 records in 18335302+0 records out 9387674624 bytes (9.4 GB) copied, 34.6279 seconds, 271 MB/s
-USR1 tells pkill to send the USR1 signal. -n and -x are just filters to make sure you send to the right process (-n sends to the newest process and -x means the process must be named exactly dd)
