diff options
| author | Fiona Klute <fiona.klute@gmx.de> | 2025-06-23 13:38:01 +0200 |
|---|---|---|
| committer | Heinrich Schuchardt <heinrich.schuchardt@canonical.com> | 2025-06-28 13:03:19 +0200 |
| commit | 97d6a2e3fe619b50303f97d0eebafaf50f1f075d (patch) | |
| tree | 9ba5ddb7008f165e6635d23aae7a1f62b5147c00 | |
| parent | 359e3012921f2fc2d43f3c4e320a752173f82b82 (diff) | |
doc: mention that extlinux.conf can use environment in "append"
This option is very useful for A/B boot setups with read-only
filesystems: Letting U-Boot fill in the rootfs (and possibly related
parameters) allows keeping all boot parameters except the actual slot
selection in the extlinux.conf file, where they can be updated easily.
Signed-off-by: Fiona Klute <fiona.klute@gmx.de>
Cc: Tom Rini <trini@konsulko.com>
| -rw-r--r-- | doc/README.pxe | 3 | ||||
| -rw-r--r-- | doc/develop/distro.rst | 7 |
2 files changed, 9 insertions, 1 deletions
diff --git a/doc/README.pxe b/doc/README.pxe index 9fff2cd5ae9..ba189080e8c 100644 --- a/doc/README.pxe +++ b/doc/README.pxe @@ -178,7 +178,8 @@ devicetree-overlay <path> [...] - if this label is chosen, use tftp to retrieve kaslrseed - set this label to request random number from hwrng as kaslr seed. append <string> - use <string> as the kernel command line when booting this - label. + label. Environment variable references like ${var} are + substituted before boot. initrd <path> - if this label is chosen, use tftp to retrieve the initrd at <path>. it will be stored at the address indicated in diff --git a/doc/develop/distro.rst b/doc/develop/distro.rst index 1d2f9c4c32b..01efce40a29 100644 --- a/doc/develop/distro.rst +++ b/doc/develop/distro.rst @@ -92,6 +92,13 @@ That said, we have some differences to these documents, namely: * If ``-`` is passed as fdt argument and ``CONFIG_SUPPORT_PASSING_ATAGS`` is enabled, then no device tree will be used (legacy booting / pre-dtb kernel). +* The ``append`` string may use environment variables. For example, an + A/B boot setup could use ``append root=PARTLABEL=root_${bootslot}`` + to set the root filesystem to the right one for the selected slot, + assuming the ``bootslot`` environment variable is set before the + extlinux.conf file is processed, and the partition is labeled to + match. + See also doc/README.pxe under 'pxe file format'. One example extlinux.conf generated by the Fedora installer is:: |