display and update information about
the top CPU processes
top displays the top processes on the
system and periodically updates this information. If standard output is an
intelligent terminal (see below) then as many processes as will fit on the
terminal screen are displayed by default. Otherwise, a good number of them
are shown (around 20). Raw CPU percentage is used to rank the processes. If
number is given, then the top
number processes will be displayed instead of the
top makes a distinction
between terminals that support advanced capabilities and those that do not.
This distinction affects the choice of defaults for certain options. In the
remainder of this document, an
terminal is one that supports cursor addressing, clear screen, and clear to
end of line. Conversely, a
terminal is one that does not support such features. If the output of
top is redirected to a file, it acts as if it were
being run on a dumb terminal.
The options are as follows:
- Display combined CPU statistics for all processors on a single line instead of one line per CPU.
- Use batch mode. In this mode, all input from the
terminal is ignored. Interrupt characters (such as
^C’ and ‘
^\’) still have an effect. This is the default on a dumb terminal, or when the output is not a terminal.
- Show command line arguments as well as the process itself.
- Show only count displays, then exit. A display is
considered to be one update of the screen. This option allows the user to
select the number of displays to be shown before
topautomatically exits. For intelligent terminals, no upper limit is set. The default is 1 for dumb terminals.
- Display only processes that contain string in their command name.
- Show process threads in the display. Normally, only the main process is shown. This option makes all threads visible.
- Do not display idle processes. By default,
topdisplays both active and idle processes.
- Use interactive mode. In this mode, any input is immediately read for processing. See the section on INTERACTIVE MODE for an explanation of which keys perform what functions. After the command is processed, the screen will immediately be updated, even if the command was not understood. This mode is the default when standard output is an intelligent terminal.
- Use non-interactive mode. This is identical to batch mode.
- Sort the process display area using the specified
field as the primary key. The field name is the name
of the column as seen in the output, but in lower case. The
OpenBSD version of
topsupports cpu, size, res, time, pri, pid, and command.
- Show only the process pid.
topto -20 so that it will run faster. This can be used when the system is being very sluggish to improve the possibility of discovering the problem. This option can only be used by root.
- Show system processes in the display. Normally, system processes such as the pager and the swapper are not shown. This option makes them visible.
- Set the delay between screen updates to time seconds. The value may be fractional, to permit delays of less than 1 second. The default delay between updates is 5 seconds.
- Show only those processes owned by user. This option currently only accepts usernames and will not understand UID numbers.
- Do not take the time to map UID numbers to usernames. Normally,
topwill read as much of the password database as is necessary to map all the user ID numbers it encounters into login names. This option disables all that, while possibly decreasing execution time. The UID numbers are displayed instead of the names.
Both count and number
fields can be specified as
infinite, indicating that
they can stretch as far as possible. This is accomplished by using any
proper prefix of the keywords
all. The default
for count on an intelligent terminal is, in fact,
The environment variable
TOP is examined
for options before the command line is scanned. This enables a user to set
his or her own defaults. The number of processes to display can also be
specified in the environment variable
-u are actually
toggles. A second specification of any of these options will negate the
first. Thus a user who has the environment variable
TOP set to “-I” may use the command
“top -I” to see idle processes.
top is running in
interactive mode, it reads commands from the terminal and
acts upon them accordingly. In this mode, the terminal is put in
CBREAK, so that a character will be processed as
soon as it is typed. Almost always, a key will be pressed when
top is between displays; that is, while it is
waiting for time seconds to elapse. If this is the
case, the command will be processed and the display will be updated
immediately thereafter (reflecting any changes that the command may have
specified). This happens even if the command was incorrect. If a key is
top is in the middle of updating the
display, it will finish the update and then process the command. Some
commands require additional information, and the user will be prompted
accordingly. While typing this information in, the user's erase and kill
keys (as set up by the command
stty(1)) are recognized, and a newline terminates the input.
These commands are currently recognized (^L refers to control-L):
- h | ?
- Display a summary of the commands (help screen).
- Redraw the screen.
- Update the screen.
- Reset any filters put in place by the ‘g’, ‘p’, and ‘u’ interactive commands, or their command line equivalents, or any process highlighting put in place by the ‘P’ interactive command.
- Toggle the display of CPU statistics.
- Toggle the display of process command line arguments.
- d count
- Show only count displays, then exit.
- Display a list of system errors (if any) generated by the last
- g string
- Display only processes that contain string in their command name. ‘g+’ shows all processes.
- Toggle the display of process threads.
- I | i
- Toggle the display of idle processes.
- k [-sig] pid
- Send signal -sig
TERMby default) to process pid. This acts similarly to the command kill(1).
- n|# count
- Show count processes.
- o field
- Sort the process display area using the specified
field as the primary key. Values are the same as for
-oflag, as detailed above.
- P pid
- Highlight a specific process, selected by pid. ‘P+’ removes process highlighting.
- p pid
- Show only the process pid. ‘p+’ shows all processes.
- r count pid
- Change the priority (the nice) of a list of processes to count for process pid. This acts similarly to the command renice(8).
- Toggle the display of system processes.
- s time
- Set the delay between screen updates to time seconds.
- u user
- Show only those processes owned by user. ‘u+’ shows processes belonging to all users.
The top few lines of the display show general information about the state of the system, including the three load average numbers, the hostname, the current time, the number of existing processes, the number of processes in each state (starting, running, idle, stopped, zombie, dead, and on processor), and a percentage of time spent in each of the processor states (user, nice, system, interrupt, and idle). It also includes information about physical and virtual memory allocation. The load average numbers give the number of jobs in the run queue averaged over 1, 5, and 15 minutes.
The remainder of the screen displays information about individual processes. This display is similar in spirit to ps(1) but it is not exactly the same. The following fields are displayed:
- The process ID.
- The name of the process's owner.
- Used instead of USERNAME if
- The current priority of the process.
- The nice amount (in the range -20 to 20).
- The total size of the process (the text, data, and stack segments).
- The current amount of resident memory.
- The current state (one of
onproc). On multiprocessor systems, this is followed by a slash and the CPU number on which the process is bound.
- A description of the wait channel the process is sleeping on if it's asleep.
- The number of system and user CPU seconds that the process has used.
- The raw percentage of CPU usage and the default field on which the display is sorted.
- The name of the command that the process is currently running. (If the process is swapped out, this column is enclosed by angle brackets.)
- User-configurable defaults for options.
- kernel memory
- physical memory
- used to map user ID to user
- kernel image
fstat(1), kill(1), netstat(1), ps(1), stty(1), systat(1), mem(4), iostat(8), pstat(8), renice(8), vmstat(8)
William LeFebvre, EECS Department, Northwestern University
As with ps(1), things can change while
collecting information for an update. The picture it gives is only a close
approximation to reality.