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.