Can't increase cpu cores on VBox vm

Question

I imported a virtual machine from another host (the original host is using VirtualBox 5.0.16 and the new host is using VirtualBox 6.1.12). This virtual machine is installed with RHEL 4 32-bit version and had only 1 core.

After importing it from another host I tried to increase the CPU cores to 6 cores since the new host has more core. I enabled "Nested Vt-x/AMD-V", "PAE/NX", and "I/O APIC" in the machine's settings.

After starting the VM, I checked the CPU using "cat /proc/cpuinfo" but it only displayed 1 core:

$ cat /proc/cpuinfo 
processor : 0 
vendor_id : Genuinelntel 
cpu family : 6 
model : 85 
model name : Intel(R) Xeon(R) Silver 4214 CPU 2.20GHz
stepping : 7 
cpu MHz : 2193.857 
cache size : 16896 KB 
fdiv_bug : no
hlt_bug : no
fOOf_bug : no
coma_bug : no
fpu : yes 
fpu_exception : yes 
cpuid level : 22
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht nx rdtscp constant_tsc pni popcnt 
bogomips : 4396.31 

While dmidecode type 4 doesn't show anything

$ dmidecode -t4
# dmidecode 2.9
SMBIOS 2.5 present.

I tried to use CPU hotplug and it still doesn't work.

Here's the info of the VM

Answer 1

This source suggests there's a package called kernel-smp that you'd need.