BLS configuration snippets

6.18 LPAR mode z/VM guest KVM guest

Using Boot Loader Specification (BLS) snippets, you can add boot configurations to zipl without editing existing configuration files.

BLS snippets are provided as configuration files in a directory that is shared across all installed operating system instances. You add a boot configuration to zipl by adding a file with a BLS snippet to this directory, /boot/loader/entries by default.

Files that contain BLS snippets can have any name, but must have the file extension .conf. To avoid naming conflicts and to provide a hint about the content, a common naming convention includes the value of /etc/machine-id, the kernel version, and an operating system identifier in the name. For example, one such file might be /boot/loader/entries/22be12d5d204461a9da34f3c3fd30ff9-5.5.0-10.s390.conf.

Depending on your distribution, the Linux® installation process might create a file with a BLS snippet for you.

BLS options

Table 1 shows the subset of BLS options that are relevant to Linux on IBM® Z.

Table 1. BLS parameters and zipl equivalents
Option	Description	zipl configuration file equivalent
`title`	A meaningful identifier for the IPL configuration. BLS configuration file `title` specifications together with their zipl configuration file equivalents must be unique within the scope of a zipl command call. The title must be the first specification within a BLS configuration file.	Section name as specified within square brackets ([ ])
`version`	Specifies a version in human readable format. For example, use the output of the uname -r command. The processing order of BLS snippets is based on an alphanumeric assessment of the values of this parameter. The intention is to make the latest operating system version the default. This item is optional.	none
`linux`	Path to a Linux kernel.	image=
`initrd`	Path to an initial RAM disk. This item is optional.	ramdisk=
`options`	Kernel parameters. This item is optional.	parameters=

Snippet syntax

Lines start with an option keyword, followed by a blank, followed by a value. The first line must specify the title option. The configuration file can include empty lines and comment lines. Comment lines start with a number sign (#).

BLS snippet example

title Linux 5.5 test kernel
#This is a comment line and is ignored
version 5.5.0-10-test
linux /boot/22be12d5d204461a9da34f3c3fd30ff9/kernels/linux-5.5.0-10
initrd /boot/22be12d5d204461a9da34f3c3fd30ff9/initrds/ramfs-5.5.0-10.im
options dasd=0.0.a01b root=/dev/dasda cio_ignore=all,!condev

Complementing BLS snippets through a zipl configuration file

You must use a zipl configuration file to complement the specifications in a BLS snippet with the target= parameter. Use the default section of the zipl configuration file to set target=.

Depending on your distribution, zipl might be installed with a default configuration file at /etc/zipl.conf, with a content similar to the following example:

[defaultboot]
defaultauto
prompt=1
timeout=5
target=/boot
secure=auto

You can optionally specify the secure= option.