Finding how much memory is available on Linux system may probably, not seem to be a complicated task. But do we really know how to extract this information correctly? I can assure you that this information is a little bit more difficult to find out, than it seems to be.
The information from ST06 is not accurate and if you want to check it out from OS level, you need to know exactly where to look.
The command for finding out the memory information is the free command:
free -m displays the memory in Mb, the free -g presents the results in gigabytes and if you add the “t” option, it will add also display the swap information:
Let’s have a look on the command and see what do the values displayed mean?
(1) => the amount of physical memory the server has
(2) => the amount of memory that is in use now
(3) => the amount of memory that is currently free
(4) => the amount of shared memory is currently used by the system
(5), (6) => the amount of cached memory that the kernel is using for filesystems buffers, etc …
(7) => the amount of memory that is really used
(8) => the amount of memory that can be free when the linux kernel will try to release it, if an application tries to allocate more that what it is free at (3). It is calculated from the values from the first line: free + buffers + cached (3) + (5) + (6)
Conclusion:
The amount of free memory from the second line cannot be considered entirely free, in case SAP and databases are running on that server, because some of the cached memory is already actively occupied by the SAP shared memory and database caches and these memory areas are needed by the applications.
So what amount of memory can be really considered available in case of need? That would be the Cached memory – Shared memory that is 2116 Mb.
This can also be calculated also from /proc/meminfo easily by the difference between Cached and Shmem 13114880 kb – 10946292 kb = 2118 Mb
Additional information:
1382721 – Linux: Interpreting the output of the command ‘free’