mjhjmtu

When in top, typing capital "E" cycles through different memory units (kb, mb, gb etc) in the total memory info:

While lower-case "e" does the same individual process lines:

From the manpage:

2c. MEMORY Usage
 This portion consists of two lines which may express values in kibibytes
 (KiB) through exbibytes (EiB) depending on the scaling factor enforced
 with the 'E' interactive command.

Version Information: top -version: procps-ng version 3.3.9 System: CentOS 7

There is a command-line option which does that:

-M : Detect memory units
 Show memory units (k/M/G) and display floating point values in the
 memory summary.

So it is sufficient to run top like that:

top -M

If -M does not work you can press E while already in top.

From man top (procps-ng version 3.3.9):

E :Extend-Memory-Scale in Summary Area
With this command you can cycle through the available summary area memory scaling which ranges from KiB (kibibytes or 1,024 bytes) through EiB (exbibytes or 1,152,921,504,606,846,976 bytes).

If you see a '+' between a displayed number and the following label, it means that top was forced to truncate some portion of that number. By raising the scaling factor, such truncation can be avoided.

You can also use htop. It's much cooler than top.

If you are using Debian or one of its derivatives, then you can install it using sudo apt-get install htop.

Edit: Here is a screenshot with a better color scheme:

top -M doesn't work on any of the Fedora, Debian or Ubuntu distros to my knowledge. I just tried it and it's not in the procps-ng package that provides top. There are many implementations of top so one needs to pay special attention to which they use.

In general it's best to use free with switching to get the amount of memory free on Linux.

procps vs. procps-ng

You might of noticed that on CentOS 5 & 6 as well as RHEL 5 & 6 that top -M appears to work. This is because those distros ship with the original version of procps. The project was forked and there is now another project procps-ng.

Some of the details as to why there was fork, from the Fedora Project's page.

excerpt

Old (legacy) procps tools had no updates for several years and that led to a massive code split caused by a local-only application of distribution specific patches, which were not merged upstream. The project became hardly maintainable since some of the newly written patches were incompatible with sources maintained by other distributors. A similar incompatibility could be noticed in the applications behavior and their command line switches. This inevitable update can be understood as an effort to unify the procps tools across all Linux distributions.

So to be clear, the forked project, procps-ng is what Debian, Fedora, Ubuntu, and other distros are using, the legacy project, which does support top -M is still in use of several of the longer term releases that don't keep up with the latest and greatest.

NOTE: I downloaded the latest version of procps-ng, "procps-ng version 3.3.9.1-14ef" and it too was lacking the -M switch.

$ ./top/top -version
 procps-ng version 3.3.9.1-14ef
Usage:
 lt-top -hv | -bcHiOSs -d secs -n max -u|U user -p pid(s) -o field -w [cols]

free

In running free with switches you can see the most likely reason as to why the lack of units feature is missing from procps-ng's implementation of top.

$ free -m
 total used free shared buffers cached
Mem: 7782 6506 1276 0 504 1726
-/+ buffers/cache: 4274 3507
Swap: 7823 1429 6394
[saml@greeneggs ~]$ free -k
 total used free shared buffers cached
Mem: 7969492 6663180 1306312 0 516948 1764780
-/+ buffers/cache: 4381452 3588040
Swap: 8011772 1463456 6548316

Rounding becomes problematic, so I believe, procps's implementation avoids the issue by not offering the ability.

htop

Does an OK job of showing aggregate memory usage.

atop

In my opinion a better tool for looking at memory.

nmon

Another useful tool is nmon for looking at system performance.

You can press the following keys:

• 
  e -- Change the scaling factor on the summary display


• 
  Shift+e -- Change the scaling factor on the task


• 
  Shift+w -- Save current settings

So the quick answer : depending on your linux distro, try either :

top -M

OR, after starting top, type capital E (then W to write the config).

One of those should work for nearly everybody (except Solaris, of course, where you'd be lucky to have top at all).

bonus tip : every time you start a top instance on a new install, type ExyzW to save colours and highlighting and units - what a relief!

On RHEL7
top
shift + e or CspsLK ON. You need " E " capital alphabet.

You will get in MiB, Gib, TiB, PiB, EiB. All these you can access.

And also you can you htop command which should be downlaoded and installed on rpm base system.

Thank you.
Sagar Dalvi