The task is (pardon the screen/text grab)

3376 jstateson	20	0 29696	-3808	3284 S	0.0	0.1	0:00.03 -bash
3407 boinc	30	10 78.8G	79014	36014 S	0.0 10.0	0:00.00 ../../projects/setiathome.berkeley.edu/setiathome_x41p_V0.98bl_x86_64-pc-linux-gnu_cuda90

so, the owner of task 3407 is "boinc" and I own 3376

using sudo kill -9 3407 has no effect when that task is "hung"

can I log in as "boinc" to terminate it? Is there a password?
Maybe it is hung so bad it cant receive the terminate signal.
Is there another way to terminate?

The task is (pardon the screen/text grab)

3376 jstateson	20	0 29696	-3808	3284 S	0.0	0.1	0:00.03 -bash
3407 boinc	30	10 78.8G	79014	36014 S	0.0 10.0	0:00.00 ../../projects/setiathome.berkeley.edu/setiathome_x41p_V0.98bl_x86_64-pc-linux-gnu_cuda90

so, the owner of task 3407 is "boinc" and I own 3376

using sudo kill -9 3407 has no effect when that task is "hung"

can I log in as "boinc" to terminate it? Is there a password?
Maybe it is hung so bad it cant receive the terminate signal.
Is there another way to terminate?

$ sudo reboot

If a sigkill is not working, it isn't a BOINC issue. Are you sure that the reaper (launchd PID 1) is able to run? It may take the O/S a while to get to it.

If you can't kill it as sudo, then you won't be able to kill it as boinc. - Unless I have completely misunderstood how Linux works.

The task is (pardon the screen/text grab)

3376 jstateson	20	0 29696	-3808	3284 S	0.0	0.1	0:00.03 -bash
3407 boinc	30	10 78.8G	79014	36014 S	0.0 10.0	0:00.00 ../../projects/setiathome.berkeley.edu/setiathome_x41p_V0.98bl_x86_64-pc-linux-gnu_cuda90

so, the owner of task 3407 is "boinc" and I own 3376

using sudo kill -9 3407 has no effect when that task is "hung"

can I log in as "boinc" to terminate it? Is there a password?
Maybe it is hung so bad it cant receive the terminate signal.
Is there another way to terminate?

$ sudo reboot

If a sigkill is not working, it isn't a BOINC issue. Are you sure that the reaper (launchd PID 1) is able to run? It may take the O/S a while to get to it.

I think that is what happened - the O/S was unable to respond. This was a 4 core system with 10 GPUs and as the motherboard had only 6 slots I had to used splitters. I was even getting periodic messages from nVidia that it had "lost" a GPU or two when reporting fan speeds. I am back to a single GPU for each slot and no problems. It did work good for a long time with 8 but when I added the last pair of gtx1060 and a second splitter all hell broke lose. It was difficult to determine which board had the problem as they had the same name "gtx1060" and I had to stop the fan with my finger and check the fan speed report to identify which board I was testing. On rare occasions i have seen windows 10 task manager unable to terminate a task but usually I don't have to manually reboot windows when this happens as it reboots itself within a second or two after a blue screen. This was the first time kill -9 did not work which I did not expect.