There are many ways to view memory usage information in Linux, but the most common methods which are available in most Linux distribution without requiring installation of additional applications are free and top.

Both free and top are command-line tools and can be run from the terminal.

Display memory usage information in Linux:

  1. Launch our preferred terminal application.
  2. Display basic memory usage information using free. 
    $ free
              total        used        free      shared  buff/cache   available
Mem:        2013428      999352      113610        6188      900376      842184
Swap:        969960         524      969436
  3. Display basic memory usage information using free in human readable format. 
    $ free -h
              total        used        free      shared  buff/cache   available
Mem:          1.9Gi       976Mi       111Mi       6.0Mi       879Mi       822Mi
Swap:         947Mi       0.0Ki       946Mi

    More options for free command: 

    $ free --help

Usage:
 free [options]

Options:
 -b, --bytes         show output in bytes
     --kilo          show output in kilobytes
     --mega          show output in megabytes
     --giga          show output in gigabytes
     --tera          show output in terabytes
     --peta          show output in petabytes
 -k, --kibi          show output in kibibytes
 -m, --mebi          show output in mebibytes
 -g, --gibi          show output in gibibytes
     --tebi          show output in tebibytes
     --pebi          show output in pebibytes
 -h, --human         show human-readable output
     --si            use powers of 1000 not 1024
 -l, --lohi          show detailed low and high memory statistics
 -t, --total         show total for RAM + swap
 -s N, --seconds N   repeat printing every N seconds
 -c N, --count N     repeat printing N times, then exit
 -w, --wide          wide output

     --help     display this help and exit
 -V, --version  output version information and exit

For more details see free(1).
  4. Display application memory usage using top. 
    $ top -n1 -o %MEM
top - 16:25:49 up 40 min,  2 users,  load average: 0.08, 0.23, 0.34
Tasks: 281 total,   1 running, 280 sleeping,   0 stopped,   0 zombie
%Cpu(s):  5.9 us, 17.6 sy,  0.0 ni, 76.5 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :   1966.2 total,    108.4 free,    975.9 used,    881.9 buff/cache
MiB Swap:    947.2 total,    946.7 free,      0.5 used.    822.1 avail Mem

   PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
  1511 user      20   0 2575320 203944  87640 S   0.0  10.1   0:44.31 gnome-shell
  1931 user      20   0  777408 119956  36288 S   0.0   6.0   0:03.91 gnome-software
  2385 user      20   0 1393488  99916  54312 S   0.0   5.0   1:04.11 rhythmbox
  2054 user      20   0 1043436  97064  44896 S   0.0   4.8   0:09.76 streamtuner2
  1745 user      20   0  803280  56900  45324 S   0.0   2.8   0:00.44 evolution-alarm
  1374 user      20   0  259016  54708  32968 S   0.0   2.7   0:15.65 Xorg
  1930 user      20   0  986610  45828  33144 S   0.0   2.3   0:04.31 gnome-terminal-
  1933 user      20   0  702652  39440  25932 S   0.0   2.0   0:00.31 seahorse
  1771 user      20   0  344420  37420  29520 S   0.0   1.9   0:03.53 vmtoolsd
  1788 user      20   0  750852  33624  28984 S   0.0   1.7   0:00.31 evolution-calen
  1589 user      20   0  628356  32944  27610 S   0.0   1.6   0:00.12 goa-daemon
  1801 user      20   0  695356  30780  27012 S   0.0   1.5   0:00.06 evolution-addre
  2341 user      20   0  518056  29224  22776 S   0.0   1.5   0:00.29 update-notifier
  1610 user      20   0  499596  28968  24656 S   0.0   1.4   0:00.12 evolution-sourc
   641 root      20   0  676140  27736  13008 S   0.0   1.4   0:03.15 snapd
   411 root      19  -1   58116  27384  25840 S   0.0   1.4   0:01.77 systemd-journal
  1553 user      20   0  295756  26080  16944 S   0.0   1.3   0:00.77 ibus-extension-
  1647 user      20   0  925768  25924  18964 S   0.0   1.3   0:00.48 gsd-media-keys
  1660 user      20   0  515152  24880  18260 S   0.0   1.2   0:00.28 gsd-color
  1640 user      20   0  369336  24764  18168 S   0.0   1.2   0:00.24 gsd-power
  1666 user      20   0  367312  24732  17764 S   0.0   1.2   0:00.31 gsd-xsettings
  1746 user      20   0  472812  23856  11652 S   0.0   1.2   0:00.25 tracker-store
  1638 user      20   0  366800  23796  17368 S   0.0   1.2   0:00.23 gsd-keyboard
  1557 user      20   0  218820  23624  17328 S   0.0   1.2   0:00.22 ibus-x11
  1576 user      20   0  518380  23408  20332 S   0.0   1.2   0:00.09 gnome-shell-cal
  1654 user      20   0  294528  23128  16672 S   0.0   1.1   0:00.22 gsd-wacom
  1652 user      20   0  218360  22776  16488 S   0.0   1.1   0:00.75 gsd-clipboard
   771 root      20   0  131004  21936  13820 S   0.0   1.1   0:00.31 unattended-upgr
  1752 user      39  19  519912  21832  14252 S   0.0   1.1   0:00.17 tracker-miner-f
  2034 root      20   0  389564  20808  17412 S   0.0   1.0   0:00.23 fwupd
  1592 user       9 -11 2217220  19200  15460 S   5.9   1.0   2:47.65 pulseaudio
   612 root      20   0   52112  18992  10972 S   0.0   0.9   0:00.23 networkd-dispat
   632 root      20   0  424316  18976  16120 S   0.0   0.9   0:00.51 NetworkManager
  1761 user      39  19  661240  18916  11748 S   0.0   0.9   0:00.15 tracker-miner-a
   835 whoopsie  20   0  331610  15532  13660 S   0.0   0.8   0:00.07 whoopsie
  1674 user      20   0  321672  15344  13440 S   0.0   0.8   0:00.02 gsd-datetime
  1382 user      20   0  583368  15296  12536 S   0.0   0.8   0:00.22 gnome-session-b
  1314 colord    20   0  257832  13772   8788 S   0.0   0.7   0:00.22 colord
  1698 user      20   0  367052  13392  11628 S   0.0   0.7   0:00.02 gsd-printer
   652 root      20   0  393988  12752  10204 S   0.0   0.6   0:00.18 udisksd
   684 root      20   0  182624  11972  10412 S   0.0   0.6   0:00.12 cups-browsed
   540 root      20   0  133576  11610  10264 S   0.0   0.6   0:02.97 vmtoolsd
  5. Display specific application memory usage using top
    $ top -n1 -o %MEM | grep rhythmbox
  2385 user      20   0 1393488  99916  54312 S   6.2   5.0   1:06.10 rhythmbox

    More options for top command: 

    $ top -help
  procps-ng 3.3.15
Usage:
  top -hv | -bcEHiOSs1 -d secs -n max -u|U user -p pid(s) -o field -w [cols]
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author: shakir
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