I'm using Ubuntu 17.04 in my laptop.

free -m command gave me the following output after i logged in to my PC and ran this command.

ubuntu@ubuntu-pc:~$ free -m
              total        used        free      shared  buff/cache   available
Mem:           3865        1527        1171         249        1167        1862
Swap:          2047           0        2047

How can i calculate the memory usage of Desktop environment(Unity) after deducting the buffer and cache.

Answers like this are bit confusing.


These tools show the memory usage of all running processes (for example when you are running Ubuntu with Unity, but no particular application program running).


I am also using

free -m  # Display the amount of memory in megabytes.

and I think the column 'used' is useful (no pun intended).

The output of free is explained in the manual

man free

DESCRIPTION free displays the total amount of free and used physical and swap memory in the system, as well as the buffers and caches used by the kernel. The information is gathered by parsing /proc/mem‐ info. The displayed columns are:


Total installed memory (MemTotal and SwapTotal in /proc/meminfo)


Used memory (calculated as total - free - buffers - cache)


Unused memory (MemFree and SwapFree in /proc/meminfo)


Memory used (mostly) by tmpfs (Shmem in /proc/meminfo, available on kernels 2.6.32, displayed as zero if not available)


Memory used by kernel buffers (Buffers in /proc/meminfo)


Memory used by the page cache and slabs (Cached and Slab in /proc/meminfo)


Sum of buffers and cache


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)


top will show the same (or almost the same) result (tested in 16.04 LTS), (but in older versions the output of top was more difficult to match to the output of free).

htop, more user friendly

You will get a similar result as 'used' with htop installed with

sudo apt install htop
  • Actually i have installed GNOME desktop environment in Ubuntu. By default unity is also there. I checked the memory usage of Unity without opening any other app after reboot and got 999 MB usage. Also in GNOME Wayland it was 1086 MB. Looks like these are such a huge memory utilization. So i just doubt if my calculations was right or not. Is this a normal utilization ? Please advice. – Rooney Nov 5 '17 at 12:45
  • These desktop environments need a lot of RAM and a fairly modern graphics chip/card to work well. If your hardware cannot perform well or you need the RAM for other purposes, you can try an Ubuntu community flavour with a lighter desktop environment, Lubuntu, Ubuntu Budgie, Ubuntu MATE or Xubuntu. – sudodus Nov 5 '17 at 12:53
  • Try them live and install the version that you like best. It is possible to install the desktop environments in the same Ubuntu system, but I think it is a bad idea, because it is very difficult to get a clean system after the testing. Instead test with live systems booted from USB and then install a separate system (dual boot) with the Ubuntu flavour you like best alongside the old system or replace the old system. – sudodus Nov 5 '17 at 12:53
  • free -m shows used 663 MiB directly after booting Ubuntu 17.10 Gnome with Wayland in my Intel NUC with simple Intel graphics. free -m shows used 270 MiB directly after booting Lubuntu 17.10 (64-bit, the 32-bit version needs less RAM) in my Toshiba laptop, also with simple Intel graphics. free -m shows used 1339 MiB in this computer (my production computer with an nvidia graphics card running Lubuntu with several tabs in Firefox plus Thunderbird and some terminal windows open). – sudodus Nov 5 '17 at 13:03
  • Okay, so i guess for me its better to switch to Lubuntu as i am using an old laptop with less amount of memory installed. – Rooney Nov 5 '17 at 13:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.