Summary

We've covered a lot of ground in this lesson, but at the same time, we've only scratched the surface. Unfortunately, there is too much to know about cron and at to fit into this 10-minute lesson. For more information, consult your local man pages. Understanding processes can be a bit difficult at first, but depending on your use of the system, you might never need to do much more than put a process into the background. If you use KDE exclusively, you'll find that processes work exactly as you might expect on any desktop operating system. In addition, you can easily open a shell prompt and use all of these commands and reference their man pages. You can also use your current X Window System help system.

The following is a quick review of what was discussed in this lesson:

• & The ampersand can be used to put a process into the background. Use this if you are running something that takes a long time to complete and that requires little or no user interaction.

• bg/fg The bg and fg commands can be used to move processes to and from background or foreground operation.

• ps To list all the processes that you are running on your system, use the ps command. You can also view processes that are controlled by other users, but you can't modify their priority or kill them.

• kill This command is used to send a signal to a process. Normally, this signal terminates the execution of the process. In other cases, it can cause a program to reread its configuration file or reinitialize itself.

• nohup Exiting a shell sends a SIGHUP (hangup) signal to all the running processes in that shell. To enable a process to continue running even after you log off, use the nohup command.

• nice/renice Every process on the computer has a priority that controls how much processor time a process gets in order to complete its task. Priorities range from -20 to 20, with the negative numbers being the higher priority.

• top The top command shows the amount of CPU time being used by the processes that are currently running on your system. The display continuously updates, so you can view how much CPU time new processes take as they are added to the system.

• at/crontab You can schedule commands to run at certain times on your system by using the at and crontab functions. You will want to check with your system administrator and read the appropriate man pages before attempting to do so.