The dmidecode command gives you all informations available about your memory.
With the special parameter “-t 16”, you can see the maximum (physical) memory that your server can have:
$ dmidecode -t 16 # dmidecode 2.8 SMBIOS 2.4 present. Handle 0x1000, DMI type 16, 15 bytes Physical Memory Array Location: System Board Or Motherboard Use: System Memory Error Correction Type: Multi-bit ECC Maximum Capacity: 32 GB Error Information Handle: Not Provided Number Of Devices: 8
Here we can see that our server can handle up to 32Gb
Check empty memory slots
To know which physical slots are used or available use the “-t 17” flag.
dmidecode -t 17 | grep Size
Size: 2048 MB
Size: 2048 MB
Size: No Module Installed
Size: No Module Installed
Size: No Module Installed
Size: No Module Installed
Size: No Module Installed
Size: No Module Installed