How can the physical RAM size be determined in Linux programatically?

On the command line this can be found out using the 'free' utility and 'cat /proc/meminfo'. What would be the different ways to find out the physical RAM size in Linu开发者_C百科x programatically from a :

1. Userspace Application
2. Kernel Module

What API calls are available ?

#include <unistd.h>

long long physical_mem_bytes = (long long) sysconf (_SC_PHYS_PAGES) * sysconf (_SC_PAGESIZE);

Other than the command line ulimit, I don't know of a way of finding maximum memory for an individual process.

Programmatically, Linux won't tell you the actual physical size. Instead you should read this info from SMBIOS with, e.g.,

sudo dmidecode -t memory | fgrep -ie 'size:'

This will give you results like the following (from a box with 4 RAM banks, only 2 installed):

Maximum Memory Module Size: 16384 MB
Maximum Total Memory Size: 65536 MB
Installed Size: 2048 MB (Single-bank Connection)
Enabled Size: 2048 MB (Single-bank Connection)
Installed Size: Not Installed
Enabled Size: Not Installed
Installed Size: 2048 MB (Single-bank Connection)
Enabled Size: 2048 MB (Single-bank Connection)
Installed Size: Not Installed
Enabled Size: Not Installed
Size: 2048 MB
Size: No Module Installed
Size: 2048 MB
Size: No Module Installed

Add the reported sizes (or Enabled Sizes, but some BIOSes empirically don't report that) to get (in this case) 4096 MB. (Extra points for code that automates the parsing and arithmetic, but you can probably do that in your head nearly as reliably.)

To check your computation, run

fgrep -e 'MemTotal:' /proc/meminfo

The value reported by /proc/meminfo should not be more than the value you compute from dmidecode. In this case, empirically I get

MemTotal:        3988616 kB

cat /proc/meminfo

specifically from memory, I got this result from what Jared said sudo dmidecode -t memory there you can read the specs for each individual memory slot, so you will read something like 2048MB, in my case I have 2 of these being 4gb, despite my non PAE kernel only shows about 3.3gb and all other applications wont say the real physical memory, only dmidecode, thx!