Red Hat Enterprise Linux 5 Administration Unleashed

60CHAPTER 2Post-Installation ConfigurationThe SELinux mode can be changed at any time by selecting the System menu from the toppanel of the desktop and selecting Administration, SELinux Management or by executingthe system-config-selinux command. After starting the tool, click the SELinux tab.When a Linux system crashes, it is sometimes possible for the kernel to output a snapshot,or dump, of the system memory. This dump can be analyzed to try and determine thecause of the crash. Kdump can be enabled with the Setup Agent as shown in Figure 2.4.FIGURE 2.4Enabling KdumpIf Kdump is enabled, a small amount of system memory is reserved so that the dump can bewritten to it and then saved to disk before the system completely crashes. If you select toenable Kdump, specify how much memory to reserve for it. To enable or disable Kdumplater, execute the system-config-kdump command to start a graphical application for configuringit. Refer to Chapter 21, “Monitoring and Tuning the Kernel,” for details on Kdump.CAUTIONKdump does not currently work with the Visualization kernel. If your kernel versionends with the keyword xen, do not enable Kdump.The system time is a crucial component of a server or desktop computer whenever filesare shared or synchronized. The Date and Time screen in Figure 2.5 can be used to set thecorrect date and time and optionally configure a Network Time Protocol (NTP) server thatsynchronizes the system’s time with a time server. For more information about NTP, referto Chapter 19, “Explaining Other Common Network Services.”