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If you have GNOME desktop available on your Linux system, System Monitor (gnome-system-monitor) is available to provide a more graphical way of displaying processes on your system. You sort processes by clicking columns. You can right-click processes to stop, kill, or renice them.

To start System Monitor from the GNOME desktop, press the Windows key and then type System Monitor and press Enter. Then select the Processes tab. Figure 6.2 shows an example of the System Monitor window, displaying processes for the current user in order by memory use.

FIGURE 6.2 Use the System Monitor window to view and change running processes.

By default, only running processes associated with your user account are displayed. Those processes are listed alphabetically at first. You can resort the processes by clicking any of the field headings (forward and reverse). For example, click the %CPU heading to see which processes are consuming the most processing power. Click the Memory heading to see which processes consume the most memory.

You can change your processes in various ways by right-clicking a process name and selecting from the menu that appears (see Figure 6.3 for an example).

Here are some of the things you can do to a process from the menu you clicked:

 Stop: Pauses the process so that no processing occurs until you select Continue Process. (This is the same as pressing Ctrl+Z on a process from the shell.)

 Continue: Continues running a paused process.

 End: Sends a Terminate signal (15) to a process. In most cases, this terminates the process cleanly.

 Kill: Sends a Kill signal (9) to a process. This should kill a process immediately, regardless of whether it can be done cleanly.FIGURE 6.3 Renice, kill, or pause a process from the System Monitor window.

 Change Priority: Presents a list of priorities from Very Low to Very High. Select Custom to see a slider bar from which you can renice a process. Normal priority is 0. To get better processor priority, use a negative number from –1 to –20. To have a lower processor priority, use a positive number (0 to 19). Only the root user can assign negative priorities, so when prompted you need to provide the root password to set a negative nice value.

 Memory Maps: Lets you view the system memory map to see which libraries and other components are being held in memory for the process.

 Open Files: Lets you view which files are currently being held open by the process.

 Properties: Lets you see other settings associated with the process (such as security context, memory usage, and CPU use percentages).

You can display running processes associated with users other than yourself. To do that, highlight any process in the display (just click it). Then, from the menu button (the button with three bars on it), select All Processes. You can modify processes you don't own only if you are the root user or if you can provide the root password when prompted after you try to change a process. Sometimes, you won't have the luxury of working with a graphical interface. To change processes without a graphical interface, you can use a set of commands and keystrokes to change, pause, or kill running processes. Some of those are described next.