Fedora Linux

? 'User Private Groups' in the Red Hat Linux 9 manual: http://www.redhat.com/docs/manuals/linux/RHL- 9-Manual/ref-guide/s1-users-groups-private-groups.html

4.9. Managing Processes

A process is a running instance of a program. If you run a program twice, two processes are created. In order to manage a Fedora system effectively, you must be able to monitor and control processes.

4.9.1. How Do I Do That?

Fedora provides multiple tools to monitor process activity and resource usage, modify process priority, and terminate processes.

Processes are identified by a Process ID (PID) number, which is sequentially assigned. There is a small set of information associated with each process, including:

nice

A value used to alter a process's scheduling priority, which determines how much CPU time the process receives. The actual priority assigned to a process is calculated based upon this factor, as well as how much CPU time the process has recently received and how many input/output (I/O) operations it has recently performed. This value is inherited by child processes.

parent process ID

The PID of the process that started the process. If the parent process disappears, this is replaced by 1 (the init process).

real user ID and effective user ID

The numeric user ID of the user actually running the program and the effective user running the program. These can be different only when the suid mechanism is active (see Lab 4.8, 'Control Access to Files '), although an effective user ID remains in effect when a suid program calls a non- suid program.

real group ID and effective group ID

The numeric group ID of the group actually running the program and the effective group running the program. These are similar to the real and effective user IDs in that they will be different only when the sgid mechanism is active.

umask

The permission mask received from the parent process.

tty

The terminal associated with the program (if applicable). This permits all programs on that terminal to receive a hangup signal (HUP) when the terminal connection is lost, which is the case when a telephone modem call is hung up, a terminal window is closed, or a remote access Telnet/SSH session is terminated. This value is inherited by child processes.

It's important to realize that at any particular point in time, most processes are sleeping while they wait for some resource to become available. That resource might be a mouse click, a keystroke, a network packet, some data from disk, or a particular time of day.

4.9.1.1. Monitoring process information graphically in GNOME

The menu item Applications>System Tools>System Monitor will run gnome-system- monitor and present the display shown in Figure 4-13.

Figure 4-13. GNOME System Monitor window

This display has two tabs:

Processes

Displays a table of current processes with information about each.

Resources

Displays scrolling graphs displaying CPU, memory, and swap usage.

By default, the Processes tab displays the name of the program executing, process status (Sleeping or Running), Virtual Memory (VM) size, percentage of CPU time, the SELinux Security Context, and the arguments used on the command line that started the process (including the command name).

The default display shows the most useful information about each process, but to configure the display to your liking, you can:

Add and remove fields

Select Edit>Preferences to view a list of available fields (columns) with a checkbox for each. Check or uncheck items to add them to or remove them from the list. Close this window when you are done editing the field list.

Reorder and resize columns

Drag column headings to rearrange the order in which they are displayed. To change a column width, click between it and an adjacent column, and then drag to the desired width.

Sort a column

Click on a column heading to select that column for the sort sequence. An arrow will appear in the header (as shown on the VM Size column in Figure 4-13 ); click on the heading again to toggle between ascending and descending sort order.

Filter by process type

The Show menu lets you select your own processes, all processes on the system, or just the active (running, not sleeping) processes.

To terminate a process, highlight it by clicking on it and then click the End Process button, type Alt-P, or right-click on the process and select End Process. If that doesn't cause the process to terminate within a few seconds, right-click on the process and select Kill Process (or highlight the process and type Ctrl-K).

You won't be able to terminate processes owned by other users (including system processes)