1.7. Variables¶
We already have seen some variables in Device parameters. But there is more to variables.
1.7.1. The global device¶
The global device is a special purpose device. It only exists as a
storage for global variables. Some global variables are created internally
in barebox (see Magic variables). Additional variables can be created with
the global - create or set global variables command:
global myvar
This creates the global.myvar variable which now can be used like any
other variable. You can also directly assign a value during creation:
global myvar1=foobar
NOTE: creating a variable with global myvar1=foobar looks very similar
to assigning a value with global.myvar1=foobar, but the latter fails when
a variable has not been created before.
1.7.2. Non volatile variables¶
Additionally to global variables barebox also has non volatile (nv) variables. Unlike the global variables the nv variables are persistent over reboots.
Each nv variable is linked with the global variable of the same name. Whenever the nv variable changes its value the corresponding global variable also changes its value. The other way round though is not true: Changing a global variable does not change the corresponding nv variable. This means that changing a global variable changes the behaviour for the currently running barebox, while changing a nv variable changes the behaviour persistently over reboots.
nv variables can be created or removed with the nv - create, set or remove non volatile (NV) variables command.
The nv variables are made persistent using the environment facilities of barebox. They are saved automatically to the storage medium whenever barebox shuts down (that is, a reset - perform RESET of the CPU is issued or a kernel is started).
examples:
barebox@Phytec phyCARD-i.MX27:/ devinfo nv
barebox@Phytec phyCARD-i.MX27:/ nv model=myboard
barebox@myboard:/ devinfo nv
Parameters:
model: myboard
barebox@myboard:/ devinfo global
Parameters:
[...]
model: myboard
[...]
barebox@myboard:/ global.model=yourboard
barebox@yourboard:/ devinfo nv
Parameters:
model: myboard
barebox@yourboard:/
1.7.3. Non volatile device variables¶
Non volatile device variables are used to make device parameters persistent. They are regular nv variables but are linked with other devices instead of the global device. Every nv variable in the form nv.dev.<devname>.<paramname> will be mirrored to the corresponding <devname>.<paramname> variable.
This example changes the partitioning of the nand0 device:
barebox@Phytec phyCARD-i.MX27:/ nv dev.nand0.partitions=4M(barebox),1M(barebox-environment),-(root)
barebox@Phytec phyCARD-i.MX27:/ devinfo nand0
Parameters:
[...]
partitions: 4M(barebox),1M(barebox-environment),8M(kernel),1011M(root)
[...]
1.8. Magic variables¶
Some variables have special meanings and influence the behaviour of barebox. Most but not all of them are consolidated in the The global device. Since it’s hard to remember which variables these are and if the current barebox has support for them the magicvar - list information about magic variables command can print a list of all active variables with special meaning along with a short description:
barebox:/ magicvar
OPTARG optarg for hush builtin getopt
PATH colon separated list of paths to search for executables
PS1 hush prompt
automount_path mountpath passed to automount scripts
bootargs Linux Kernel parameters
bootsource The source barebox has been booted from
bootsource_instance The instance of the source barebox has been booted from
global.boot.default default boot order
...
Above output will only list magic variables that were compiled. Below is a full listing of all currently documented magic variables:
1.8.1. No prefix¶
Variable |
Description |
|---|---|
|
Previous working directory, set by cd and used by ‘cd -’ |
|
optarg for hush builtin getopt |
|
colon separated list of paths to search for executables |
|
command to execute prior to each primary prompt |
|
hush prompt |
|
mountpath passed to automount scripts |
|
Linux kernel parameters |
|
boot file name to request from the DHCP server |
|
The source barebox has been booted from |
|
The instance of the source barebox has been booted from |
|
Enable permanent writes (fuse blowing) to the BSEC OTP |
|
Whether the FPGA is configured and in user mode |
|
Enable permanent writes (fuse blowing) to the OCOTP via the ELE |
|
If false, loads prints a dot every 100 lines instead of echoing them |
|
Mode of the first USB OTG port: otg, host or peripheral |
|
Name of the active security policy (read-only) |
|
Whether the FPGA is programmed |
1.8.2. efi.*¶
Variable |
Description |
|---|---|
|
Revision of the EFI firmware |
|
Vendor of the EFI firmware |
|
semicolon-separated list of RFC 4646 formatted languages for PlatformLangCodes |
|
EFI loader state (inactive, boot, runtime) |
|
Major version of the EFI specification implemented by the firmware |
|
Minor version of the EFI specification implemented by the firmware |
|
The arch-specific removable media path |
|
UEFI Secure Boot is enabled |
|
UEFI Secure Boot is enabled and the firmware is not in Setup Mode |
1.8.2.1. efi.vars.*¶
Variable |
Description |
|---|---|
|
efiloader: Size in bytes of the memory area reserved for keeping UEFI variables |
|
efiloader: Name of file within ESP to store variables to (WARNING: Not power-fail safe!) |
1.8.3. fw_cfg.*¶
Variable |
Description |
|---|---|
|
Access QEMU fw_cfg via port I/O instead of DMA |
|
QEMU fw_cfg item accessed through /dev/fw_cfg |
1.8.4. global.*¶
Variable |
Description |
|---|---|
|
9P debugging level |
|
Allow colored console output |
|
Name of architecture as used by Linux |
|
Autoboot state. Possible values: countdown (default), abort, halt, menu, boot |
|
Which key allows to interrupt autoboot. Possible values: ‘any’, ‘ctrl-c’ or any other single ascii character. |
|
Timeout before autoboot starts in seconds |
|
version of buildsystem barebox was built with |
|
If true, scripts can be aborted with ctrl-c |
|
The barebox endianness |
|
The path the environment is stored |
|
Firmware search path |
|
shortname of the board. Also used as hostname for DHCP requests |
If true, use a stream_id per host controller and not per device |
|
|
Maximum number of messages kept in the log buffer |
|
Console log level: only messages up to this level are printed |
|
Persistent device-specific, hexadecimal, 32-character id |
|
Product name of this hardware |
|
Sets both NFS -o {port.mountport}= to the specified non-zero value |
|
Partition binding for kernel device tree fixups: new, legacy, donttouch or adaptive |
|
byte offset used by free-space searches for new partitions |
|
SMBIOS-reported product UUID |
|
Board serial number |
|
SoC Unique ID |
|
Raw SoC Unique ID representation |
|
TFTP windowsize to request for downloads, capped at CONFIG_FS_TFTP_MAX_WINDOW_SIZE |
|
Next tutorial step. |
|
Username used by the default environment to construct network boot paths |
|
The barebox version |
1.8.4.1. global.boot.*¶
Variable |
Description |
|---|---|
|
default boot order |
|
If set, only boot bootloader spec entries with a matching machine-id |
|
Watchdog enable timeout in seconds before booting |
1.8.4.2. global.bootchooser.*¶
Variable |
Description |
|---|---|
|
bootchooser: Default number of attempts for a target |
|
bootchooser: Default priority for a target |
|
bootchooser: Disable target when remaining attempts counter reaches 0 |
|
bootchooser: Choose condition to reset number of attempts for all enabled targets (‘power-on’, ‘all-zero’, ‘reset’) |
|
bootchooser: Choosen condition to reset priority of all targets (default: ‘’, ‘all-zero’) |
|
bootchooser: Try again when booting a target fails |
|
bootchooser: state name prefix, empty for nv backend |
|
bootchooser: Space separated list of target names |
1.8.4.3. global.bootm.*¶
Variable |
Description |
|---|---|
|
Add root= option to Kernel to mount rootfs from the device the Kernel comes from (default, device can be overridden via global.bootm.root_dev) |
|
bootm default dryrun level |
|
Add earlycon option to Kernel for early log output |
|
efiloader: Behavior for EFI-stubbable boot images: EFI “disabled”, EFI if “available” (default), EFI is “required” |
|
bootm default boot image |
|
bootm default boot image loadaddr |
|
bootm default initrd |
|
bootm default initrd loadaddr |
|
bootm default oftree |
|
If true, append systemd.hostname=$global.hostname to Kernel command line |
|
If true, append systemd.machine_id=$global.machine_id to Kernel command line |
|
Add barebox.security.policy= option to Kernel |
|
bootm default root device (overrides default device in global.bootm.appendroot) |
|
bootm root parameter name (normally ‘root’ for root=/dev/…) |
|
bootm default verbosity level (0=quiet) |
|
bootm default verify level |
1.8.4.4. global.dhcp.*¶
Variable |
Description |
|---|---|
|
bootfile returned from DHCP request |
|
client id to send to the DHCP server |
|
client uuid to send to the DHCP server |
|
hostname to send to the DHCP server (default: global.hostname) |
|
NTP server used when none is given explicitly |
|
OF tree returned from DHCP request (option 224) |
|
private data to send to the DHCP server (option 224) |
|
retry limit |
|
rootpath returned from DHCP request |
|
TFTP server Name returned from DHCP request |
|
user class to send to the DHCP server |
|
vendor id to send to the DHCP server |
1.8.4.5. global.fastboot.*¶
Variable |
Description |
|---|---|
|
Export barebox update handlers via fastboot |
|
Fastboot maximum download size |
|
If true, automatically start fastboot over UDP during startup |
|
Partitions exported for update via fastboot |
1.8.4.6. global.linux.*¶
Variable |
Description |
|---|---|
|
Linux blkdevparts variables |
|
append to original oftree bootargs |
|
Use legacy x86 handover protocol instead of StartImage BootService |
|
Linux mtdparts variables |
|
Options appended to the nfsroot= Linux parameter (default: v3,tcp) |
|
Argument (in seconds) for Linux rootwait= option if it’s fixed up. A negative value waits indefinitely |
1.8.4.7. global.linux.bootargs.*¶
Variable |
Description |
|---|---|
|
Linux bootargs variables |
|
console= argument for Linux from the stdout-path property in /chosen node |
1.8.4.8. global.login.*¶
Variable |
Description |
|---|---|
|
command to run when password entry failed |
|
timeout to type the password |
1.8.4.9. global.mtd_peb.*¶
Variable |
Description |
|---|---|
|
If true, written data will be verified |
|
random bitflips, on average every #nth access returns -EUCLEAN |
|
random erase failures, on average every #nth access returns erase failure |
|
random write failures, on average every #nth access returns write failure |
1.8.4.10. global.net.*¶
Variable |
Description |
|---|---|
|
Domain name used for DNS requests |
|
The directory within which artifacts are fetched for network boot targets (/mnt/tftp by default) |
|
The network gateway used when a host is not in any directly visible subnet |
|
net: force detection of devices on ifup -a |
|
The DNS server used for resolving host names |
|
Standard server used for NFS/TFTP |
1.8.4.11. global.of.*¶
Variable |
Description |
|---|---|
|
Extra machine/board compatible to prepend to kernel DT compatible |
1.8.4.12. global.of.overlay.*¶
Variable |
Description |
|---|---|
|
space separated list of compatibles an overlay must match |
|
space separated list of filters |
|
Path to look for dt overlays or a path to a FIT image |
|
space separated list of filename or fit config-node name patterns an overlay must match |
1.8.4.13. global.system.*¶
Variable |
Description |
|---|---|
|
When true, refresh GPT partitions when necessary |
|
board-specific list of updatable partitions |
|
The reason for the last system reset |
|
The reset reason instance number |
1.8.4.14. global.system.reboot_mode.*¶
Variable |
Description |
|---|---|
|
reboot-mode: Mode to set next, to be evaluated after reset |
|
reboot-mode: Mode set previously, before barebox start |
1.8.4.15. global.ubifs.*¶
Variable |
Description |
|---|---|
|
If true, allow to mount authenticated UBIFS images without doing authentication |
|
If true, allow to mount UBIFS with encrypted files |
1.8.4.16. global.usbgadget.*¶
Variable |
Description |
|---|---|
|
usbgadget: Create CDC ACM function |
|
usbgadget: Automatically start usbgadget on boot |
|
usbgadget: Create DFU function |
1.8.5. ocotp0.*¶
Variable |
Description |
|---|---|
|
Alias for ocotp0.mac_addr0 |
|
MAC address of the first Ethernet controller in the fuses |
|
MAC address of the second Ethernet controller in the fuses (SoCs with two MACs only) |
|
Read the fuses directly instead of from the shadow registers |
1.8.6. soc0.*¶
Variable |
Description |
|---|---|
|
SoC family |
|
Machine model, defaults to the device tree model property |
|
SoC silicon revision |
|
SoC unique ID |
|
SoC model |
1.8.7. arm-specific variables¶
Variable |
Description |
|---|---|
|
ARM machine ID |
|
ARM system revision |
|
ARM system serial |
|
If true, ignore device tree and boot using ATAGs |
|
ARM security state to start the kernel in: secure, nonsecure or hyp |
|
MAC addresses in the fuses, one per barebox,provide-mac-address entry |
|
Read the fuses by explicit sensing instead of from the shadow registers |
|
Enable permanent writes (fuse blowing) to the IIM |
|
Enable permanent writes (fuse blowing) to the OCOTP |
|
PSCI conduit: smc or hvc |
|
PSCI version implemented by the firmware |
|
AT91 SoC name |
|
AT91 SoC subtype name |
|
Global general storage register 0 |
|
Global general storage register 1 |
|
Global general storage register 2 |
|
Global general storage register 3 |
|
Persistent global general storage register 0 |
|
Persistent global general storage register 1 |
|
Persistent global general storage register 2 |
|
Persistent global general storage register 3 |
1.8.8. kvx-specific variables¶
Variable |
Description |
|---|---|
|
KVX architecture revision |
|
KVX board sn |
|
KVX MPPA chip id |
1.8.9. riscv-specific variables¶
Variable |
Description |
|---|---|
|
RISC-V hartid |
1.8.10. Board-specific variables¶
1.8.10.1. beaglebone¶
Variable |
Description |
|---|---|
|
The board variant |
1.8.10.2. crystalfontz-cfa10036¶
Variable |
Description |
|---|---|
|
The board variant |
1.8.10.3. kindle-mx50¶
Variable |
Description |
|---|---|
|
The bootmode in ATAG_BOOTMODE to fill /proc/bootmode |
|
The wifi MAC in ATAG_MACADDR visible as /proc/mac_addr |
|
The postmode in ATAG_BOOTMODE to fill /proc/postmode |
|
The boardid in ATAG_REVISION16 to fill /proc/boardid |
|
The sec code in ATAG_MACADDR visible as /proc/mac_sec |
|
The device serial in ATAG_SERIAL16, visible in /proc/cpuinfo |
1.8.10.4. kindle-mx6sl¶
Variable |
Description |
|---|---|
|
The bootmode in ATAG_BOOTMODE to fill /proc/bootmode |
|
The wifi MAC in ATAG_MACADDR visible as /proc/mac_addr |
|
The postmode in ATAG_BOOTMODE to fill /proc/postmode |
|
The boardid in ATAG_REVISION16 to fill /proc/boardid |
|
The sec code in ATAG_MACADDR visible as /proc/mac_sec |
|
The device serial in ATAG_SERIAL16, visible in /proc/cpuinfo |
1.8.10.5. raspberry-pi¶
Variable |
Description |
|---|---|
|
Boot mode reported by the VideoCore firmware |
|
Boot partition reported by the VideoCore firmware |
|
Kernel command line from the VideoCore device tree |
|
Default kernel image name for the CPU: kernel.img, kernel7.img or kernel8.img |
|
os_prefix from the VideoCore device tree |
|
overlay_prefix from the VideoCore device tree |
1.8.10.6. rockchip-rk3568-bpi-r2pro¶
Variable |
Description |
|---|---|
|
The board hardware ID |
1.8.10.7. rockchip-rk3568-evb¶
Variable |
Description |
|---|---|
|
The board hardware ID |
1.8.10.8. skov-arm9cpu¶
Variable |
Description |
|---|---|
|
The detected memory size in MiB |
