Chapter 25: Gathering System Information

Sometimes you may need 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 Linux system using simple commands and a few simple programs.

System Processes

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 themselves, use the command ps aux. This list is a static list; in other words, it is a snapshot of what is running when you invoke the command.

If you want a constantly updated list of running processes, use the top command (as described later in this section).

The ps output can be long. To prevent it from scrolling off the screen, you can pipe it through less:

ps aux | 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:

ps ax | grep emacs

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 as follows:

  6:14pm up 2 days, 19:29, 5 users, load average: 0.10, 0.06, 0.07 71 processes: 68 sleeping, 2 running, 1 zombie, 0 stopped CPU states:  2.7% user,  0.5% system,  0.0% nice,  96.6% idle Mem:   256812K av,  252016K used,    4796K free,   97228K shrd,   43300K buff Swap:  265032K av,    1328K used,  263704K free                   86180K cached   PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME COMMAND 15775 joe        5   0 11028  10M  3192 S     1.5  4.2   0:46 emacs 14429 root      15   0 63620  62M  3284 R     0.5 24.7  63:33 X 17372 joe       11   0  1056 1056   840 R     0.5  0.4   0:00 top 17356 joe        2   0  4104 4104  3244 S     0.3  1.5   0:00 gnome-terminal 14461 joe        1   0  3584 3584  2104 S     0.1  1.3   0:17 sawfish     1 root       0   0   544  544   476 S     0.0  0.2   0:06 init     2 root       0   0     0    0     0 SW    0.0  0.0   0:00 kflushd     3 root       1   0     0    0     0 SW    0.0  0.0   0:24 kupdate     4 root       0   0     0    0     0 SW    0.0  0.0   0:00 kpiod     5 root       0   0     0    0     0 SW    0.0  0.0   0:29 kswapd   347 root       0   0   556  556   460 S     0.0  0.2   0:00 syslogd   357 root       0   0   712  712   360 S     0.0  0.2   0:00 klogd   372 bin        0   0   692  692   584 S     0.0  0.2   0:00 portmap   388 root       0   0     0    0     0 SW    0.0  0.0   0:00 lockd   389 root       0   0     0    0     0 SW    0.0  0.0   0:00 rpciod   414 root       0   0   436  432   372 S     0.0  0.1   0:00 apmd   476 root       0   0   592  592   496 S     0.0  0.2   0:00 automount

To exit top, press the q key.

Table 25-1 lists some of the more useful interactive commands that you can use with top.

Table 25-1: Interactive top Commands

Command	Description
Spacebar	Immediately refresh the display.
h	Display a help screen.
k	Kill a process. You will be prompted for the process ID and the signal to send to it.
n	Change the number of processes displayed. You will be prompted to enter the number.
u	Sort by user.
M	Sort by memory usage.
P	Sort by CPU usage.

If you prefer a graphical interface for top, you can use the GNOME System Monitor. To start the System Monitor from the desktop, click the Main Menu button and choose System Tools > System Monitor (or type gnome-system-monitor at a shell prompt from within the X Window System). Then select the Process Listing tab.

The GNOME System Monitor allows you to search for processes in the list of running process as well as 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 will be 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.

25-1. : GNOME System Monitor — Process Listing Tab

By default, the GNOME System Monitor does not display threads. To change this preference, choose Edit > Preferences, click the Process Listing tab, and select Show Threads. The preference also allows you to configure the update interval, what type of information to display about each process by default, and the colors of the system monitor graphs.