Documentation
The remaining Table of Contents
OVERVIEW
Operation
Linux Memory Types
1. COMMAND-LINE Options
2. SUMMARY Display
a. UPTIME and LOAD Averages
b. TASK and CPU States
c. MEMORY Usage
3. FIELDS / Columns Display
a. DESCRIPTIONS of Fields
b. MANAGING Fields
4. INTERACTIVE Commands
a. GLOBAL Commands
b. SUMMARY AREA Commands
c. TASK AREA Commands
1. Appearance
2. Content
3. Size
4. Sorting
d. COLOR Mapping
5. ALTERNATE-DISPLAY Provisions
a. WINDOWS Overview
b. COMMANDS for Windows
c. SCROLLING a Window
d. SEARCHING in a Window
e. FILTERING in a Window
6. FILES
a. PERSONAL Configuration File
b. ADDING INSPECT Entries
c. SYSTEM Configuration File
d. SYSTEM Restrictions File
7. STUPID TRICKS Sampler
a. Kernel Magic
b. Bouncing Windows
c. The Big Bird Window
d. The Ol' Switcheroo
8. BUGS, 9. SEE Also
Operation
When operating top, the two most important keys are the help (h
or ?) key and quit (`q') key. Alternatively, you could simply
use the traditional interrupt key (^C) when you're done.
When started for the first time, you'll be presented with these
traditional elements on the main top screen: 1) Summary Area; 2)
Fields/Columns Header; 3) Task Area. Each of these will be
explored in the sections that follow. There is also an
Input/Message line between the Summary Area and Columns Header
which needs no further explanation.
The main top screen is generally quite adaptive to changes in
terminal dimensions under X-Windows. Other top screens may be
less so, especially those with static text. It ultimately
depends, however, on your particular window manager and terminal
emulator. There may be occasions when their view of terminal
size and current contents differs from top's view, which is
always based on operating system calls.
Following any re-size operation, if a top screen is corrupted,
appears incomplete or disordered, simply typing something
innocuous like a punctuation character or cursor motion key will
usually restore it. In extreme cases, the following sequence
almost certainly will:
key/cmd objective
^Z suspend top
fg resume top
<Left> force a screen redraw (if necessary)
But if the display is still corrupted, there is one more step you
could try. Insert this command after top has been suspended but
before resuming it.
key/cmd objective
reset restore your terminal settings
Note: the width of top's display will be limited to 512
positions. Displaying all fields requires approximately 250
characters. Remaining screen width is usually allocated to any
variable width columns currently visible. The variable width
columns, such as COMMAND, are noted in topic 3a. DESCRIPTIONS of
Fields. Actual output width may also be influenced by the -w
switch, which is discussed in topic 1. COMMAND-LINE Options.
Lastly, some of top's screens or functions require the use of
cursor motion keys like the standard arrow keys plus the Home,
End, PgUp and PgDn keys. If your terminal or emulator does not
provide those keys, the following combinations are accepted as
alternatives:
key equivalent-keys
Left alt + h
Down alt + j
Up alt + k
Right alt + l
Home alt + ctrl + h
PgDn alt + ctrl + j
PgUp alt + ctrl + k
End alt + ctrl + l
The Up and Down arrow keys have special significance when
prompted for line input terminated with the <Enter> key. Those
keys, or their aliases, can be used to retrieve previous input
lines which can then be edited and re-input. And there are four
additional keys available with line oriented input.
key special-significance
Up recall older strings for re-editing
Down recall newer strings or erase entire line
Insert toggle between insert and overtype modes
Delete character removed at cursor, moving others left
Home jump to beginning of input line
End jump to end of input line
Linux Memory Types
For our purposes there are three types of memory, and one is
optional. First is physical memory, a limited resource where
code and data must reside when executed or referenced. Next is
the optional swap file, where modified (dirty) memory can be
saved and later retrieved if too many demands are made on
physical memory. Lastly we have virtual memory, a nearly
unlimited resource serving the following goals:
1. abstraction, free from physical memory addresses/limits
2. isolation, every process in a separate address space
3. sharing, a single mapping can serve multiple needs
4. flexibility, assign a virtual address to a file
Regardless of which of these forms memory may take, all are
managed as pages (typically 4096 bytes) but expressed by default
in top as KiB (kibibyte). The memory discussed under topic `2c.
MEMORY Usage' deals with physical memory and the swap file for
the system as a whole. The memory reviewed in topic `3. FIELDS /
Columns Display' embraces all three memory types, but for
individual processes.
For each such process, every memory page is restricted to a
single quadrant from the table below. Both physical memory and
virtual memory can include any of the four, while the swap file
only includes #1 through #3. The memory in quadrant #4, when
modified, acts as its own dedicated swap file.
Private | Shared
1 | 2
Anonymous . stack |
. malloc() |
. brk()/sbrk() | . POSIX shm*
. mmap(PRIVATE, ANON) | . mmap(SHARED, ANON)
-----------------------+----------------------
. mmap(PRIVATE, fd) | . mmap(SHARED, fd)
File-backed . pgms/shared libs |
3 | 4
The following may help in interpreting process level memory
values displayed as scalable columns and discussed under topic
`3a. DESCRIPTIONS of Fields'.
%MEM - simply RES divided by total physical memory
CODE - the `pgms' portion of quadrant 3
DATA - the entire quadrant 1 portion of VIRT plus all
explicit mmap file-backed pages of quadrant 3
RES - anything occupying physical memory which, beginning with
Linux-4.5, is the sum of the following three fields:
RSan - quadrant 1 pages, which include any
former quadrant 3 pages if modified
RSfd - quadrant 3 and quadrant 4 pages
RSsh - quadrant 2 pages
RSlk - subset of RES which cannot be swapped out (any quadrant)
SHR - subset of RES (excludes 1, includes all 2 & 4, some 3)
SWAP - potentially any quadrant except 4
USED - simply the sum of RES and SWAP
VIRT - everything in-use and/or reserved (all quadrants)
Note: Even though program images and shared libraries are
considered private to a process, they will be accounted for as
shared (SHR) by the kernel.
