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Operating Systems Linux Red Hat Concept of free –m command in Linux Post 302758705 by sixstrings on Sunday 20th of January 2013 02:02:32 PM
Old 01-20-2013
Code:
             total       used       free     shared    buffers     cached
Mem:          3816       3569        247          0        118       2397
-/+ buffers/cache:       1053       2763
Swap:         3823         13       3810

ok, this is the output for my laptop.

The free command is used to display the amount of free and used memory on a system. The -m option tells free to print the output in MB.

My laptop has 4Gb currently.

Linux attempts to utilize all of the memory on the system and not leave any sitting idle, like some other operating systems have done over time. Memory will be used for the OS and applications, but the remainder will be used as "buffers and cache". The kernel will keep items in memory that are needed often or are predicted to be needed for faster access. The memory used for "buffers and cache" is available for applications or the OS to use. If required, it is quickly flushed and used.

To find the actual available memory on my system, take the last number on the Mem line (247) and add it to the last number on the Mem line (2397). So currently, I have about 3G of memory available.

Most of this information is available via the manpage and simple google searches. Take a look and you should have all of your questions answered.
 

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sg_get_mem_stats(3)					     Library Functions Manual					       sg_get_mem_stats(3)

NAME
sg_get_mem_stats, sg_get_swap_stats - get VM statistics SYNOPSIS
#include <statgrab.h> sg_mem_stats *sg_get_mem_stats(void); sg_swap_stats *sg_get_swap_stats(void); DESCRIPTION
Memory statistics are accessed through the sg_get_mem_stats function. It returns a pointer to a static sg_mem_stats. The sg_get_swap_stats returns returns swap statistics. It returns a pointer to a static sg_swap_stats. On the FreeBSD operating system elevated privileges are required to access the swap statistics. Making the program setgid kmem should be sufficient. Programs running as root will not have this problem. RETURN VALUES
The VM system calls can return a pointer to either a sg_mem_stats or a sg_swap_stats. typedef struct{ long long total; long long free; long long used; long long cache; }sg_mem_stats; total The total amount of memory in bytes. free The total free memory in bytes. used The total used memory in bytes. cache The amount of cache used in bytes. typedef struct{ long long total; long long used; long long free; }sg_swap_stats; total The total swap space in bytes. used The used swap in bytes. free The free swap in bytes. TODO
Add a function to hold open the file descriptor to the kernel memory structures. Doing this would allow the elevated privileges to be dropped early on. SEE ALSO
statgrab(3) WEBSITE
http://www.i-scream.org/libstatgrab/ i-scream $Date: 2005/04/25 11:25:45 $ sg_get_mem_stats(3)
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