linux - top (1)
NAME
top - display top CPU processes
SYNOPSIS
top [-] [d delay] [q] [S] [s] [i]
DESCRIPTION
top provides an ongoing look at processor activity in real
time. It displays a listing of the most CPU-intensive
tasks on the system, and can provide an interactive inter-
face for manipulating processes.
COMMAND-LINE OPTIONS
d Specifies the delay between screen updates. You can
change this with the s interactive command.
q This causes top to refresh without any delay. If the
caller has superuser priviledges, top runs with the
highest possible priority.
S Specifies cumulative mode, where each process is
listed with the CPU time that it as well as its dead
children has spent. This is like the -S flag to
ps(1). See the discussion below of the S interactive
command.
s Tells top to run in secure mode. This disables the
potentially dangerous of the interactive commands
(see below). A secure top is a nifty thing to leave
running on a spare terminal.
i Start top ignoring any idle or zombie processes. See
the interactive command i below.
FIELD DESCRIPTIONS
top displays a variety of information about the processor
state. The display is updated every 5 seconds by default,
but you can change that with the d command-line option or
the s interactive command.
uptime
This line displays the time the system has been up,
and the three load averages for the system. The load
averages are the average number of process ready to
run during the last 1, 5 and 15 minutes. This line
is just like the output of uptime(1).
processes
The total number of processes running at the time of
the last update. This is also broken down into the
number of tasks which are running, sleeping, stopped,
CPU states
Shows the percentage of CPU time in user mode, system
mode, niced tasks, and idle. (Niced tasks are only
those whose nice value is negative.) Time spent in
niced tasks will also be counted in system and user
time, so the total will be more than 100%.
Mem Statistics on memory usage, including total available
memory, free memory, used memory, shared memory, and
memory used for buffers.
Swap Statistics on swap space, including total swap space,
available swap space, and used swap space. This and
Mem are just like the output of free(1).
PID The process ID of each task.
USER The user name of the task's owner.
PRI The priority of the task.
NI The nice value of the task. Negative nice values are
lower priority.
SIZE The size of the task's code plus data plus stack
space, in kilobytes, is shown here.
RSS The total amount of physical memory used by the task,
in kilobytes, is shown here.
SHRD The amount of shared memory used by the task is shown
in this column.
ST The state of the task is shown here. The state is
either S for sleeping, D for uninterruptible sleep, R
for running, Z for zombies, or T for stopped or
traced.
TIME Total CPU time the task has used since it started.
If cumulative mode is on, this also includes the CPU
time used by the process's children which have died.
You can set cumulative mode with the S command line
option or toggle it with the interactive command S.
%CPU The task's share of the CPU time since the last
screen update, expressed as a percentage of total CPU
time.
%MEM The task's share of the physical memory.
COMMAND
The task's command name, which will be truncated if
tasks will only have the name of the program in
parentheses (for example, "(getty)").
INTERACTIVE COMMANDS
Several single-key commands are recognized while top is
running. Some are disabled if the s option has been given
on the command line.
^L Erases and redraws the screen.
h or ?
Displays a help screen giving a brief summary of com-
mands, and the status of secure and cumulative modes.
k Kill a process. You will be prompted for the PID of
the task, and the signal to send to it. For a normal
kill, send signal 15. For a sure, but rather abrupt,
kill, send signal 9. The default signal, as with
kill(1), is 15, SIGTERM. This command is not avail-
able in secure mode.
i Ignore idle and zombie processes. This is a toggle
switch.
n or #
Change the number of processes to show. You will be
prompted to enter the number. This overrides auto-
matic determination of the number of processes to
show, which is based on window size measurement. If
0 is specified, then top will show as many processes
as will fit on the screen; this is the default.
q Quit.
r Re-nice a process. You will be prompted for the PID
of the task, and the value to nice it to. Entering a
positve value will cause a process to be niced to
negative values, and lose priority. If root is run-
ning top, a negative value can be entered, causing a
process to get a higher than normal priority. The
default renice value is 10. This command is not
available in secure mode.
S This toggles cumulative mode, the equivalent of ps
-S, i.e., that CPU times will include a process's
defunct children. For some programs, such as compil-
ers, which work by forking into many seperate tasks,
normal mode will make them appear less demanding than
they actually are. For others, however, such as
shells and init, this behavior is correct. In any
case, try cumulative mode for an alternative view of
CPU use.
prompted to enter the delay time, in seconds, between
updates. Fractional values are recognized down to
microseconds. Entering 0 causes continuous updates.
The default value is 5 seconds. Note that low values
cause nearly unreadably fast displays, and greatly
raise the load. This command is not available in
secure mode.
NOTES
This proc-based top works by reading the files in the proc
filesystem, mounted on /proc. If /proc is not mounted,
top will not work.
%CPU shows the cputime/realtime percentage in the period
of time between updates. For the first update, a short
delay is used, and top itself dominates the CPU usage.
After that, top will drop back, and a more reliable esti-
mate of CPU usage is available.
The SIZE and RSS fields don't count the page tables and
the task_struct of a process; this is at least 12K of mem-
ory that is always resident. SIZE is the virtual size of
the process (code+data+stack).
Keep in mind that a process must die for its time to be
recorded on its parent by cumulative mode. Perhaps more
useful behavior would be to follow each process upwards,
adding time, but that would be more expensive, possibly
prohibitively so. In any case, that would make top's
behavior incompatible with ps.
SEE ALSO
ps(1), free(1), uptime(1), kill(1), renice(1).
BUGS
If the window is less than about 70x7, top will not format
information correctly.
AUTHOR
top was originally written by Roger Binns, based on Branko
Lankester's (lankeste@fwi.uva.nl) ps program. Robert
Nation (nation@rocket.sanders.lockheed.com) re-wrote it
significantly to use the proc filesystem, based on Michael
K Johnson's (johnsonm@sunsite.unc.edu) proc-based ps pro-
gram. Many changes were made, including secure and cumu-
lative modes and a general cleanup, by Michael Shields
(mjshield@nyx.cs.du.edu).