Concepts Glossary 154 Getting Started Guide If you are logged in as the root user, you can change any user’s password, for example, to disable a user’s account temporarily: passwd username For additional system security, OpenLinux uses a password system called shadow passwords, which allows the root user to set up requirements for each user, such as how long a password can be used before being changed, and how many characters the password must contain. See the passwd man page for details on using these features. See also login, users Permissions, File See Access Rights ping Command When you have established networking on your Linux system, the ping com- mand can be used to test your network connection. When you “ping” another computer, you should receive back a simple confirmation of the exchange of net- work data. Using ping shows that the network connection has been established. The ping command can be used with either an IP address or a domain name. For example, if you use a command like this one, using an IP address for a computer that want to check your connection to: ping 192.168.45.22 and you receive a response, then you know that the network is connected. If you use this command, with a domain name for the computer you want to check: ping chicago.xyzcorp.com and you receive a response, then you also know that the name resolution is also working. Root user The root user on a Linux system is the superuser or system administrator. When you log in as root, you can perform any task on your Linux system. This also poses a danger, however, because you could accidentally damage some files while working as root. For this reason, never log in as root unless you are going