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44.6.3. IBM S/390 and IBM System z Systems

The IBM S/390 and IBM System z systems use z/IPL as the boot loader, which uses /etc/zipl.conf as the configuration file. Confirm that the file contains a section with the same version as the kernel package just installed:
[defaultboot] default=old target=/boot/
Notice that the default is not set to the new kernel. To configure z/IPL to boot the new kernel by default, change the value of the default variable to the name of the section that contains the new kernel. The first line of each section contains the name in brackets.
After modifying the configuration file, run /sbin/zipl as root to enable the changes.
Begin testing the new kernel by rebooting the computer and watching the messages to ensure that the hardware is detected properly.