exited on signal 11 (core dumped)

[meimi]

Hello,
  I find out the following lines in /var/log/messages:
May  9 13:03:52 pang /kernel: pid 48170 (rsync), uid 0: exited on signal 11 (core dumped)

This line appear whenever I tried to update ports. I know rsync is a program for file transfer, 
but what does the error mean?
and why does the error occur?

Thanks
meimi