Web site layout - 262 CHAPTER 16 TAKING CONTROL OF THE
262 CHAPTER 16 TAKING CONTROL OF THE SYSTEM With any luck, the process (and the program in question) will disappear. If it doesn t, the process you ve killed might be the child of another process that also must be killed. To track down the parent process, you need to configure topto add the PPID field, for the parent process ID, to its display. To add this field, type f, and then b. Press Enter to return to the process list. The PPID column will appear next to the process name on the right of the window. It simply shows the PID of the parent process. You can use this information to look for the parent process within the main list of processes. The trick here is to make sure that the parent process isn t something that s vital to the running of the system. If it isn t, you can safely kill it. This should have the result of killing the child process you uncovered prior to this. Caution If the PPID field in top displays a value of 1, that means the process doesn t have a parent process. In both the PPID and PID fields, you should always watch out for low numbers, particularly one-, two- or three-digit numbers. These are usually processes that started early on when Linux booted and that are essential to the system. Controlling Zombie Processes Zombie processes are those that are children of processes that have terminated. However, for some reason, they failed to take their child processes with them. Zombie processes are rare on most Linux systems. Despite their name, zombie processes are harmless. They re not actually running and don t take up system resources. However, if you want your system to be spick-and-span, you can attempt to kill them. In the top-right area of top, you can see a display that shows how many zombie processes are running on your system, as shown in Figure 16-3. Zombie processes are easily identified because they have a Z in the status (S) column within top s process list. To kill a zombie process, type k, and then type its PID. Then type 9, rather than accept the default signal of 15. Figure 16-3. You can see at a glance how many zombie processes are on your system by looking at the top right of top s display.