NAME

       u-boot-update - program to generate u-boot menu files

SYNOPSIS

       u-boot-update

DESCRIPTION

       u-boot-update  is  a  tool  used to generate the menu files used by the U-BOOT bootloader.
       Options can be configured in /etc/default/u-boot.

       For each <version> of linux kernel installed, menu items for each of <U_BOOT_ALTERNATIVES>
       are generated for the first valid entry among these:

       • fdt <U_BOOT_FDT_DIR><version>/<U_BOOT_FDT>

       • fdtdir <U_BOOT_FDT_DIR><version>/

       • fdt /<U_BOOT_FDT>

       • fdt /dtb-<version>

       Paths  without  <U_BOOT_FDT_DIR>  are considered only when <U_BOOT_FDT_DIR> is left at its
       default value.

       When root (/) and boot (/boot) are mounted on separate  filesystems,  paths  are  examined
       with /boot prepended (i.e. variables should be defined without it).

OPTIONS

       U_BOOT_UPDATE="true|false"
           This  variable specifies if u-boot-update is allowed to modify the configuration files
           in /boot/extlinux.  Values are either 'true' or 'false', default is 'true'.

       U_BOOT_ALTERNATIVES="default recovery"
           This variable  specifies  which  entries  u-boot-update  is  populating.   Values  are
           'default', 'recovery', 'live', default is 'default recovery'.

       U_BOOT_DEFAULT="l0"
           This  variable  specifies the default entry to boot.  The name of an entry consists of
           two or three characters.  Linux kernel images start with the letter 'l',  followed  by
           an  integer  started  by  '0'  for  the first kernel version (which is numerically the
           highest one in case kernel images of more than one linux version are  installed)  and,
           optionally, the mode (r for rescue mode, l for live mode).  Memdisk entries start with
           the letter 'm', followed by an integer, no optional modes available.  The  default  is
           'l0'.

       U_BOOT_ENTRIES="all"
           This  variables specifies how many kernel versions should be used to populate the boot
           configuration.  Value is an integer starting with 1, or  'all'  to  populate  for  all
           kernels, default is 'all'.

       U_BOOT_MENU_LABEL="Debian GNU/Linux, kernel"
           This  variable  specifies  the  text  that  is used as a description in the boot menu.
           Value is an arbitrary string.  If not specified, PRETTY_NAME from  /etc/os-release  is
           used.  Otherwise, it defaults to 'Debian GNU/Linux, kernel'.

       U_BOOT_PARAMETERS="ro earlycon"
           This  variable  specifies  additional boot parameters that are appended to each kernel
           entry.  Value is an arbitrary string, default is 'ro earlycon'  (except  for  recovery
           entries, where quiet is avoided).

       U_BOOT_ROOT="root=DEVICE"
           This  variable  specifies  the  root  partition.   It  is automatically extracted from
           /etc/fstab.  U-BOOT supports both devices and UUIDs.

       U_BOOT_TIMEOUT="50"
           This variable specifies the time that U-BOOT should wait for user input  during  boot.
           Values  are  in  decisecond  greater  than  0  (e.g.  '10'  for a 1 second timeout), 0
           specifies to wait forever.  The default is 50.

       U_BOOT_FDT_DIR="/usr/lib/linux-image-"
           This variable specifies the unversioned stem of paths where U-BOOT should look for the
           flattened device tree binaries.  Default is '/usr/lib/linux-image-'.

       U_BOOT_FDT="device-tree.dtb"
           This  variable  specifies  filename  or trailing part of path for a single device tree
           binary.  Default is 'device-tree.dtb'.

       U_BOOT_FDT_OVERLAYS_DIR="/boot/dtbo"
           This variable specifies the unversioned stem of paths where U-BOOT should look for the
           flattened device tree overlays binaries.  Default is '/boot/dtbo/'.

       U_BOOT_FDT_OVERLAYS="device-tree.dtbo"
           This  variable  specifies  filenames  or trailing part of path for device tree overlay
           binaries.  Default is not set.

       U_BOOT_INITRD="initrd.img"
           This variable specifies the unversioned stem  of  initramfs  filename.   If  versioned
           filename  exists  (e.g.  'initrd.img-5.10.0-8-armmp-lpae')  then  this filename set as
           option 'initrd', otherwise if unversioned filename exists (e.g. 'initrd.img) then that
           is  set  as  option  'initrd',  otherwise  option  'initrd'  is  not  set.  Default is
           'initrd.img'.

FILES

       /etc/default/u-boot

HOMEPAGE

       More information about U-BOOT can be found at <http://www.denx.de/wiki/U-Boot>.

       u-boot-update and this manual page was written by Daniel Baumann <daniel.baumann@progress-
       technologies.net>  for extlinux.  Riku Voipio <riku.voipio@linaro.org> updated them for u-
       boot.  Jonas Smedegaard <dr@jones.dk> updated misc. later changes.