Problem using dd within bash script

[Sebastian Rückerl]

Hello,

Lately I am playing around with some bash scripting that involves dd.

Everything seems to work fine as long as I am not trying to interrupt this 
process (using CTRL-C).
Only in this case everything just freezes for some time (for about 1 minute the 
terminal is blocked) even if I try to kill it from another terminal using its 
pid. This includes that all further CTRL-C are just printed to the terminal and 
nothing happens.

My workaround now is to manage all the signal handling on my own. This seems to 
work if my only goal was not to have the terminal beeing somehow not 
responsive, but it does not kill the dd. (Which can still be seen using ps ax | 
grep dd) Anyways dd is somehow interrupted (but not killed totally) as it no 
longer responds to kill -USR1.

my current solution is:
----------
#!/bin/bash

# some more things are done in the first place, not related to the dd

dd if=$1 of=$2 bs=4M &
dd_pid=$!

control_c (){
        echo "Aborting due to interrupt. Disk will most likely be useless."
        kill -9 $dd_pid
        exit 1
}

# trap keyboard interrupt (control-c)
trap control_c SIGINT

while   ps | grep " $dd_pid "
do
        # get some status information
        kill -USR1 $dd_pid
        sleep 3
done

wait $dd_pid
ret=$?
# do some more error handling and continue with the script.
------------

the whole script is executed as root. $1 is a file (image of sd-card), $2 is 
the path to the sd-card (e.g. /dev/sdc)

Can those (still somehow running) dd instances do any harm? Or are they just 
waiting for something before they can be destroyed?


Thank you for every answer that helps to clearify it all.

Cheers,
Sebastian

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