Before you learn how to configure your system, you should learn how to
gather essential system information. For example, you should know how to
find the amount of free memory, the amount of available hard drive space,
how your hard drive is partitioned, and what processes are running. This
chapter discusses how to retrieve this type of information from your Red Hat Enterprise Linux
system using simple commands and a few simple programs.
The ps ax command displays a list of current system
processes, including processes owned by other users. To display the
owner of the processes, along with the processes, use the command
ps aux. This list is a static list; in other words,
it is a snapshot of what was running when you invoked the command. If you
want a constantly updated list of running processes, use
top as described below.
The ps output can be long. To prevent it from
scrolling off the screen, you can pipe it through less:
You can use the ps command in combination with the
grep command to see if a process is running. For
example, to determine if Emacs is
running, use the following command:
The top command displays currently running processes
and important information about them including their memory and CPU
usage. The list is both real-time and interactive. An example of
top's output is provided as follows:
top - 14:01:42 up 9 days, 23:48, 4 users, load average: 0.10, 0.13, 0.07
Tasks: 96 total, 2 running, 94 sleeping, 0 stopped, 0 zombie
Cpu(s): 2.3% us, 0.3% sy, 0.0% ni, 95.4% id, 2.0% wa, 0.0% hi, 0.0% si
Mem: 645712k total, 613184k used, 32528k free, 176124k buffers
Swap: 1310712k total, 0k used, 1310712k free, 226136k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
10456 root 14 -1 31408 17m 4828 S 2.3 2.7 158:16.98 X
18110 root 16 0 3032 1052 840 R 0.7 0.2 0:00.07 top
1 root 16 0 3036 560 480 S 0.0 0.1 0:00.98 init
2 root 34 19 0 0 0 S 0.0 0.0 0:00.10 ksoftirqd/0
3 root 5 -10 0 0 0 S 0.0 0.0 0:00.07 events/0
4 root 5 -10 0 0 0 S 0.0 0.0 0:00.01 khelper
5 root 15 -10 0 0 0 S 0.0 0.0 0:00.00 kacpid
17 root 5 -10 0 0 0 S 0.0 0.0 0:00.00 kblockd/0
18 root 15 0 0 0 0 S 0.0 0.0 0:00.00 khubd
27 root 20 0 0 0 0 S 0.0 0.0 0:00.00 pdflush
28 root 15 0 0 0 0 S 0.0 0.0 0:01.96 pdflush
30 root 12 -10 0 0 0 S 0.0 0.0 0:00.00 aio/0
29 root 16 0 0 0 0 S 0.0 0.0 0:01.98 kswapd0
103 root 25 0 0 0 0 S 0.0 0.0 0:00.00 kseriod
173 root 23 0 0 0 0 S 0.0 0.0 0:00.00 scsi_eh_0
174 root 15 0 0 0 0 S 0.0 0.0 0:00.00 ahc_dv_0
177 root 20 0 0 0 0 S 0.0 0.0 0:00.00 scsi_eh_1 |
To exit top, press the [q] key.
Table 40-1 contains useful interactive
commands that you can use with top. For more
information, refer to the top(1) manual page.
| Command | Description |
|---|
| [Space] | Immediately refresh the display |
| [h] | Display a help screen |
| [k] | Kill a process. You are prompted
for the process ID and the signal to send to it. |
| [n] | Change the number of processes
displayed. You are prompted to enter the number. |
| [u] | Sort by user. |
| [M] | Sort by memory usage. |
| [P] | Sort by CPU usage. |
Table 40-1. Interactive top commands
If you prefer a graphical interface for top, you can
use the GNOME System Monitor. To start it
from the desktop, select (the main menu on the
panel) => => or type
gnome-system-monitor at a shell prompt (such as an
XTerm). Select the Process Listing tab.
The GNOME System Monitor allows you to search
for a process in the list of running process as well as to view all
processes, your processes, or active processes.
To learn more about a process, select it and click the More
Info button. Details about the process is displayed at
the bottom of the window.
To stop a process, select it and click End
Process. This function is useful for processes that have
stopped responding to user input.
To sort by the information in a specific column, click on the name of
the column. The column that the information is sorted by appears in a
darker gray color.
