Thread: Why does the prior level change in this case.

I need to undertand why the following works the way it does.

When I do something like

cat < /dev/zero | grep "f" > /dev/null &

And then exit the bash shell, I see the following on top

Code:

 PID USERNAME PRI NICE  SIZE   RES STATE    WAIT     TIME    CPU COMMAND
 4372 cd    64    0  164M  146M sleep    biowai  84:25  8.01% grep
 5664 _postfix   2    0  820K  884K sleep    select  86:57  0.00% qmgr

Now I do the same thing again. Ie

cat < /dev/zero | grep "f" > /dev/null &

But instead of exiting, I kill the bash session. Which in turn logs me out. When this happens, 2 minutes later, I see

Code:

  PID USERNAME PRI NICE  SIZE   RES STATE    WAIT     TIME    CPU COMMAND
 4372 cd    -5    0  164M  146M sleep    biowai  84:25  8.01% grep
 5664 _postfix   2    0  820K  884K sleep    select  86:57  0.00% qmgr

Ie, the PRI changes from 64 to -5 and as a result, the system starts to slow. What would trigger such behavior?

The priority is a dynamic value. You shouldn't expect it to remain the same every time you look at it. It's part of the scheduling algorithm.