# 9.2 Process Priorities

We want to discover the amount of CPU cores within the server we are working on. And we want to fully use each CPU core of the server. 

### Check Number of Cores
To determine the number of cores using, we can use the file ```/proc/cpuinfo``` and the ```grep``` command:
```bash
[greater@rhcsa ~]$ grep -c processor /proc/cpuinfo 
```

Now we want to use these CPU cores completely. We can use 1 CPU core completely with the ```sha1sum /dev/zero &``` command twice. So we would need to start this command double the amount of times to the amount of CPU cores in the server.

Go ahead and start two ```sha1sum /dev/zero &``` commands for each CPU core.
```bash
[greater@rhcsa ~]$ sha1sum /dev/zero &
```

Verify that you have all the background jobs running that you expected (two for every core in your system).
```bash
[greater@rhcsa ~]$ jobs
```

Inspect the CPU usage (as a percentage) of all your ```sha1sum``` processes, using the ```ps``` and ```grep``` commands. What do you notice?
```bash
[greater@rhcsa ~]$ ps u | grep sha1shum
-bash: psgrep: command not found
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
student+  1322  0.0  0.1 115392  2068 pts/0    Ss   23:43   0:00 -bash
student+  1349  100  0.0 116604  1128 pts/0    R    23:44   2:42 sha1sum /dev/zero
student+  1350 99.6  0.0 116604  1128 pts/0    R    23:44   2:39 sha1sum /dev/zero
student+  1353  0.0  0.0 151036  1728 pts/0    R+   23:46   0:00 ps u
```

### Check CPU 
You should notice that the cpu usage on both process is almost the same.

Use the killall  command to terminate all your sha1sum processes.
```bash
[greater@rhcsa ~]$ killall sha1sum
```

Start two ```sha1sum /dev/zero &``` commands for each of your cores, but give exactly one of them a nice level of 10.
```bash
[greater@rhcsa ~]$ sha1sum /dev/zero &
```
```bash
[greater@rhcsa ~]$ sha1sum /dev/zero &
```
```bash
[greater@rhcsa ~]$ nice -n10 sha1sum /dev/zero &
```
```bash
[greater@rhcsa ~]$ ps -o pid,pcpu,nice,comm $(pgrep sha1sum)
  PID %CPU  NI COMMAND
 1359 93.3   0 sha1sum
 1360 97.7   0 sha1sum
 1361	 6  10 sha1sum
```

### Nice and Renice
Use the renice command to set the nice level of the sha1sum with a nice level of 10 down to 5. The PIO should still be visible in the output of the previous step. Did this work? Why not?
```bash
[greater@rhcsa ~]$ renice -n 5 1361
```

As a non-privileged user, you’re not allowed to do a renice.

Using the sudo and renice commands, set the nice level for  the process you identified  in the previous step to -10.
```bash
[greater@rhcsa ~]$ sudo renice -n 5 1361
```

Start the top command as root, then use top to lower the nice level for the sha1sum
process using the most CPU back down to 0. What do you observe afterwards?

Press r to enter renice mode, then enter the PIO you identified, or press Enter if the offered default PIO is the one you want.
 Enter 0, then press Enter.
All sha1sum commands are again using an (almost) equal amount of CPU.
 Important: clean up by exiting top and killing all your sha1sum processes.
 
 
 **Extras**. One liner to start double the amount of commands to each core. Replace the "echo core" text with the command you want to start.
 
 Neat way of one liner (used by most, understood by fewer):
 ```bash
 COMMAND='echo core'; AMOUNT_PER_CORE="2"; CORES=$(grep -c processor /proc/cpuinfo); 
 CORES=$(($CORES*$AMOUNT_PER_CORE)) COUNT="0"; while [ $COUNT -lt $CORES ]; do $COMMAND; 
 COUNT=$(($COUNT+1)); done
 ```
 
 Quick and dirty (one liner on the go):
 ```bash
 COUNT="0"; while [ $COUNT -lt $(grep -c processor /proc/cpuinfo) ]; do echo core;
 echo core; COUNT=$(($COUNT+1)); done
 ```