BLS configuration snippets

Red Hat Enterprise Linux 9.2 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/36851bb476df410181cc114154a8a524-4.18.0-80.el8.s390x.conf.

Red Hat® Enterprise Linux® creates 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. 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 5.14 kernel
version 5.14.0-127.el9.s390x
linux /boot/vmlinuz-5.14.0-127.el9.s390x
initrd /boot/initramfs-5.14.0-127.el9.s390x.img
options root=/dev/disk/by-path/ccw-0.0.6500-part1 rd.dasd=0.0.6500 cio_ignore=all,!condev rd.znet=qeth,0.0.bdf0,0.0.bdf1,0.0.bdf2,layer2=1,portno=0
id -20220720114512-5.14.0-127.el9.s390x

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

Optionally, you can specify the secure= option.