Why Is the Memory of an ECS Obtained by Running the free Command Inconsistent with the Actual Memory?
After an ECS is created, run the free -m command to view the ECS memory. The query result is less than the memory configured during ECS creation.
An example is provided as follows:
For example, you set memory to 4,194,304 KB (4,096 MB) when creating the ECS. After the ECS is created, run the free -m command to view its memory. The command output is as follows:
[root@localhost ~]# free -m total used free shared buff/cache available Mem: 3790 167 3474 8 147 3414 Swap: 1022 0 1022
The memory in the command output is 3790 MB, which is less than the configured 4096 MB.
Run the dmidecode -t memory command to check the actual memory configured for the ECS. The command output is as follows:
[root@localhost ~]# dmidecode -t memory # dmidecode 3.0 Getting SMBIOS data from sysfs. SMBIOS 2.8 present. Handle 0x1000, DMI type 16, 23 bytes Physical Memory Array Location: Other Use: System Memory Error Correction Type: Multi-bit ECC Maximum Capacity: 4 GB Error Information Handle: Not Provided Number Of Devices: 1 Handle 0x1100, DMI type 17, 40 bytes Memory Device Array Handle: 0x1000 Error Information Handle: Not Provided Total Width: Unknown Data Width: Unknown Size: 4096 MB Form Factor: DIMM Set: None Locator: DIMM 0 Bank Locator: Not Specified Type: RAM Type Detail: Other Speed: Unknown Manufacturer: QEMU Serial Number: Not Specified Asset Tag: Not Specified Part Number: Not Specified Rank: Unknown Configured Clock Speed: Unknown Minimum Voltage: Unknown Maximum Voltage: Unknown Configured Voltage: Unknown
The memory in the command output is the same as that configured during ECS creation.
When the OS is started, related devices are initialized, which occupies memory. In addition, when the kernel is started, it also occupies memory. The memory occupied by kdump can be set. Unless otherwise specified, do not change the memory size occupied by kdump.
The command output of free -m shows the available memory of the ECS, and that of dmidecode -t memory shows the hardware memory.
Therefore, the memory obtained by running the free -m command is less than the memory configured for the ECS. This is a normal phenomenon.
Physical servers also have this issue.