Chris Tyler - Fedora Linux

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. Click on the heading again to toggle between ascending and descending sort order.

Filter by process type

The pull-down menu at the bottom of the display enables you to choose whether to display all processes, system processes (such as servers), user processes for all users, or just your own processes.

To terminate a process, right-click on the process and select Send Signal→SIGTERM. If that doesn't cause the process to terminate within a few seconds, highlight the process and then click the Kill button in the lower-right corner of the window (right-click on the process and select Send Signal→SIGKILL).

Just like the GNOME System Monitor, the KSysGuard program can't terminate processes owned by other users (including system processes) when run by a normal user. To run the program as root :

# ksysguard

KSysGuard can monitor many aspects of system status in addition to the process table; it's also capable of monitoring remote systems. See the KSysGuard Manual for details (press F1 in the KSysGuard window).

A similar tool is available for character-mode displays, named top :

$ top

The output from top is shown in Figure 4-15 .

Like the graphical process monitors, top updates its display regularlyevery three seconds by default. You can customize the display using the controls shown in Table 4-15 .

Figure 4-15. Output from top

Table 4-15. Top customization options

To end a process, type k (for kill ). Type in the process ID and press Enter; top will prompt you for the signal to be used. Press Enter to accept the default (15). If the process does not terminate within a few seconds, repeat the procedure with the signal 9.

Instead of using top to continuously monitor information, you can use the ps (process status) command to display a snapshot of the process table at a particular point in time.

By default, ps shows only processes executed by you on the current terminal:

$ ps

PID TTY TIME CMD

14797 pts/1 00:00:00 bash

22962 pts/1 00:00:00 ps

This shows the process ID, terminal device ( pts/1 means /dev/pts/1 ), total amount of CPU time consumed (less than one second in this example), and the command executed. This information alone is rarely useful, so ps is almost always used with some arguments.

ps uses options to select the processes to be displayed. The most useful ones are:

-A-e

All (or everyone's) processes

-u user

Processes owned by user (which can be a username or numeric user ID)

Other options are used to control the output format:

-f

Displays full information, including the UID, PID, PPID, start time (STIME), terminal (TTY), total CPU time used (TIME), and command (CMD).

-F

Displays extra-full information: everything included in -f , plus the processor number of the CPU the program is running on (PSR) and the approximate kilobytes of RAM used (RSS).

Like ls , the ps command has dozens of options. The Fedora version of ps can use Unix System V syntax or BSD syntax, so many option letters have two meanings; the one that is used depends on whether the option is specified with or without a hyphen!

To see the full documentation for ps, view the manpage but be prepared to take some time; it's over 16 pages long!

You can terminate processes by command name or by PID. When you terminate a process by name, you save yourself the hassle of looking up the PID, but if there is more than one process of the same name running, you will kill them all.

To kill by command name:

$ killall xclock

If the process doesn't terminate within a few seconds, add the -KILL argument:

$ killall -KILL xclock

Note that this will kill only processes of that name that are owned by you ; you don't have permission to kill other users' processes unless you are root . You will see an error message if other users have a process of the same name running, but this will not affect the killing of the processes that you own.

To kill PID 48292:

$ kill 48292

Again, if that doesn't work within a reasonable period of time, add the -KILL argument:

$ kill -KILL 48292

The Linux kernel has only two basic functions for starting processes: fork( ) and exec( ) .

fork( ) makes an exact copy of the current process and starts it running. exec( ) replaces the currently running program with a new program, running in the same process. So to get a new program running, the shell uses fork( ) to create a child process (a copy of the shell) and then uses exec( ) to change the program running in the child process.

When a child process is created, a number of variables are inherited from the parent process, including the real and effective user IDs, the real and effective group IDs, the umask , the terminal, the current working directory, and the environment variables.

Processes are generally permitted to run on a CPU until their timeslice the amount of time allocated to them by the scheduling algorithmis over, at which point another process is scheduled to be run.

However, processes frequently give up the CPU early because they reach a point when they need a resource to continue; this is called blocking . This is often due to slow input/output operations; no matter how fast your disk drive is, the CPU is still faster, so when one process is waiting for disk data, another process can be executing.

The difference between your typing speed and your CPU speed is even greater; most people type six characters per second or less, so on a 3 GHz PC, the CPU will average at least 500 million operations between keystrokes.