Getting Started Guide 153 cally will not affect the other programs running on the system, whether they have been started by you or by another user. Multitasking in Linux is pre-emptive. This means that the Linux kernel controls which program is running, and can take back control or end a program that is not behaving properly. Many utilities are included with Linux to allow the root supe- ruser to review and manage all of the processes running on the Linux system. Examples include the Process Management tool on the KDE Utilities menu, and the commands ps, ktop, nice, and jobs. As an example, you can see the processes that are running on your Linux system by executing this command: ps aux See also daemon, kernel Multi-user Linux is a multi-user operating system. This means that you can create multiple user accounts, each with a separate home directory to contain user data, and each with distinct security access to the Linux system. By accessing Linux remotely via a serial connection (such as a modem or dumb terminal), or via a network connection (such as an Ethernet LAN), all of your user accounts can be in use at the same time. Linux allows each user to access the system and run programs simultaneously. Unlike some operating systems, you cannot use a Linux system unless you first log in using a valid username (and password, if defined for that user). Passwords Passwords are a key part of keeping your Linux system secure. Every user account on your system should have a password. This password must be entered after the username each time someone logs in to your Linux system. If another person obtains a user’s password, that person can log in and access or destroy all of the files in that user’s control. You can change your password at any time using the passwd command: passwd You are then prompted to enter a new password twice. Passwords should consist of at least five characters, including at least one numeric digit or punctuation mark to make the password harder to obtain by unauthorized users.