What do the changes in `free` output from 14.04 to 16.04 mean?
I noticed that the free
command reporting has changed somewhere between Trusty and Xenial. Here is what `free -m' shows on one of my Trusty computers:
$ free -m
total used free shared buffers cached
Mem: 7916 7645 271 99 455 1764
-/+ buffers/cache: 5426 2490
Swap: 24999 805 24194
Here is the equivalent on (a different) Xenial system:
$ free -m
total used free shared buff/cache available
Mem: 3553 1192 857 16 1504 2277
Swap: 3689 0 3689
The +/- buffers/cache line, which I mainly used to look at, is gone. How should I interpret the new numbers?
- Does Mem used/free include buffers and cache or not?
- Which numbers are the equivalent of the used and free numbers on the "+/- buffers/cache" line of the earlier version?
Solution 1:
Please consider the sample output I got from the free
command in my Ubuntu 12.04
:
total used free shared buffers cached
Mem: 8074640 6187480 1887160 377056 365128 2113156
-/+ buffers/cache: 3709196 4365444
Swap: 15998972 82120 15916852
The Mem used
(kb_main_used) field value is now calculated like this:
used = total - free - cached - buffers
Previously, it used to be:
used = total - free
This change was introduced in the following commit https://gitlab.com/procps-ng/procps/commit/6cb75efef85f735b72e6c96f197f358f511f8ed9
An intermediate value:
buffers_plus_cached = buffers (kb_main_buffers) + cached (kb_main_cached) = 365128 + 2113156 = 2478284
+/- buffers/cache value is calculated like this:
buffers = kb_main_used - buffers_plus_cached = 6187480 - 2478284 = 3709196
/
cache = kb_main_free + buffers_plus_cached = 1887160 + 2478284 = 4365444
The new buff/cache value is calculates like this:
buff/cache = kb_main_buffers+kb_main_cached = 365128 + 2113156 = 2478284
This is the same as the buffers_plus_cached
, used in previous versions, the difference is that previously it was used internally, and now its displayed directly, and the further calculated line, -/+ buffers/cache
has been removed
For more info, please check these commits, where these changes were introduced: https://gitlab.com/procps-ng/procps/commit/f47001c9e91a1e9b12db4497051a212cf49a87b1 https://gitlab.com/procps-ng/procps/commit/c9908b59712d1afd6b9bf7971ba1d8900ae5adb8
As of the new available
field, for Linux kernels older than 2.6.27, its value is the same as the free
value, but for the later versions of the Kernel, its a bit different:
Estimation of how much memory is available for starting new
applications, without swapping. Unlike the data provided by the
cache or free fields, this field takes into account page cache
and also that not all reclaimable memory slabs will be reclaimed
due to items being in use (MemAvailable in /proc/meminfo,
available on kernels 3.14, emulated on kernels 2.6.27+,
otherwise the same as free)
Courtesy: http://manpages.ubuntu.com/manpages/xenial/en/man1/free.1.html
So, the specific answer to your questions would be:
- The new version of
free
includes buffers/cache in the calculations ofMem used/free
values. - The
+/- buffers/cache
value that used to be there in previous versions offree
is now available as:-
-/+ buffers/cache
used
= CurrentMem used
column (Its calculation is detailed above) -
-/+ buffers/cache
free
is available as the more accurate value in the current new columnavailable
-
-/+ buffers/cache
N.B: The kb_*
variable names are the internal names used in the source code.