How to check size of memory, HDD and vCPU ?

Memory

[user@host ~]$ cat /proc/meminfo
MemTotal:        4057244 kB
MemFree:         1139004 kB

...

vCPU

[user@host ~]$ grep processor /proc/cpuinfo
processor       : 0
processor       : 1

Disk info

[user@host ~]$ df -h --total

See the last line of output for total size.

In case you created Physical volume groups, you must use :

[user@host ~]$ pvdisplay