Red Hat Enterprise Linux 5 Administration Unleashed

Saving Kernel Dumps for Analysis 435The Kexec program has command-line options in addition to the -l option to load a newkernel. Command-line options for all architectures can be found in Table 21.3. Additionalcommand-line options exist per architecture. Execute the kexec -h command to view alist of these arch-specific options.21TABLE 21.3 Command-Line Options for kexecCommand-Line Option Description-h Display list of command-line options with brief descriptions.-v Display the Kexec version.-f Force an immediate warm boot without calling shutdown.-x Do not bring down the network interfaces. Must be the lastoption specified.-l Load the specified kernel into the current loaded kernel.-p Load the new kernel for use on panic.-u Unload the currently loaded Kexec kernel.-e Execute the currently loaded Kexec kernel. The kexec -ecommand will reboot the system with the kernel loaded withthe -l command.-t=Provide the type of the kernel loaded with the -l option.--mem-min= Provide the lowest memory address to load code into.--mem-max= Provide the highest memory address to load code into.Reserving Memory for the Secondary KernelEven though Kdump is compiled into the kernel, you must enable it and configure a fewsettings such as how much memory to reserve for the second kernel booted with Kexecand where to save the kernel dump file.If Kdump is activated, when a crash occurs, Kexec is used to boot in to a second kernel.This second kernel captures the kernel dump file. This is possible because the first kernelreserves memory for the second kernel to boot. The second kernel can boot with very littlememory. Because the reserved memory is used to boot the second kernel, the memorycontents of the first kernel are still available for the second kernel to create the dump file.The amount of reserved memory is set as a kernel parameter in the boot loader configurationfile. For x86 and x86_64, edit the /etc/grub.conf file as root and append the followingto the end of the kernel line in the active boot stanza:crashkernel=128M@16MFor ia64 systems, edit /etc/elilo.conf as root and add the following to the end of theline starting with append in the active boot stanza:crashkernel=256M@256M