Modifying the kernel command line parameters

To configure some of the features and capabilities used in this paper, like HiperSockets™, it is necessary to modify the kernel command line.

To modify the kernel command line in a KVM on Z release, the file /etc/zipl.conf must be modified. Use vi or a preferred text editor to open /etc/zipl.conf:

[root@kvmhost ~]# vi /etc/zipl.conf

Details about zipl.conf can be viewed using man zipl.conf. The zipl.conf file is organized into sections. The topmost section typically contains the default boot options that the system will use unless the user manually interrupts the normal boot process.

The default boot section is typically followed by one or more OS boot configs. Each boot config starts with bootid enclosed in square brackets ([ and ]). The following lines contain a number of key=value pairs describing attributes and settings used in this boot config. For readability, a key/value pair is normally placed on a separate line.

The kernel boot option modifications used in this paper are all made or added to the parameter= keyword. Keys can accept multiple values or other key=value pairs separated by spaces, as long as the entire set of values is enclosed with quotes.

After making changes or additions to the kernel boot parameter values, save and exit the file.

To apply the changes made to zipl.conf, use the following command:

[root@kvmhost ~]# zipl -V

The zipl command parses and applies the zipl.conf contents, making them available at the next system restart. Since the kernel command line options are only loaded at boot time, it is necessary to restart the system after any kernel command line changes.

After rebooting, the changes should be present in the active kernel command line. The following command can be used to check:

[root@kvmhost ~]# cat /proc/cmdline