Linux: add vCPUs to a vm/virtual machine

Add the additional CPU from the hypervisor then:

From CLI:

1. Check to see how many cpusa are shoowing up. CPU count will start at 0.

lscpu

2. Scan for missing CPUs

echo 1 | tee /sys/devices/system/cpu/cpu*/online

3. Add CPUs

Add all:
echo 1 | tee /sys/devices/system/cpu/cpu*/online
or
for a in /sys/devices/system/cpu/cpu*/online; do echo "1" > "$a"; done

Add one at a time:
echo 1 > /sys/devices/system/cpu/cpu2/online

4. Additionally: Tak a cpu offline

echo 1 > /sys/devices/system/cpu/cpu2/offline