Update Environment Variables
This guide describes how to use U-Boot to view and edit U-Boot and Linux® environment variables.
Entering U-Boot Shell
To enter the U-Boot shell, hit any key during the boot countdown.
U-Boot 2016.01 (Apr 30 2016 - 14:23:32 +0900) DRAM: 896 MiB HW Revision: 1 MMC: NEXELL DWMMC: 0, NEXELL DWMMC: 1 In: serial Out: serial Err: serial Net: eth0: ethernet@c0060000 Hit any key to stop autoboot: 0 ARTIK5#
U-Boot Environment Variables
The U-Boot environment is a block of memory that is kept in persistent storage and copied to RAM when U-Boot starts. It is used to store environment variables, which can be used to configure the system. The environment is protected by a CRC32 checksum.
Note: Editing U-Boot environment variables can affect boot controls, so do not edit them without knowledge of the system.
Print Environment Variables (printenv)
The printenv command lists the current environment variables and their settings.
ARTIK5# printenv
android_boot=setenv bootargs ${console} root=/dev/ram0 ${opts};run boot_cmd_initrd
android_format=gpt write mmc 0 $partitions_android;setenv bootcmd run android_boot;saveenv; mmc rescan; fastboot
baudrate=115200
boot_cmd=fatload mmc 0:1 $kernel_addr $kernel_file;fatload mmc 0:1 $fdtaddr $fdtfile;bootz $kernel_addr - $fdtaddr
boot_cmd_initrd=fatload mmc 0:1 $kernel_addr $kernel_file;fatload mmc 0:1 $fdtaddr $fdtfile;fatload mmc 0:1 $initrd_addr $initrd_file;bootz $kernel_addr $initrd_addr $fdtaddr
bootcmd=run ramfsboot
bootdelay=3
bootpart=1
console=console=ttySAC2,115200n8
consoleoff=set console=ram; saveenv; reset
consoleon=set console=console=ttySAC2,115200n8
fdtaddr=40800000
fdtfile=exynos3250-artik5.dtb
initrd_addr=43000000
initrd_file=uInitrd
kernel_addr=40008000
kernel_file=zImage
mmcboot=setenv bootargs ${console} root=/dev/mmcblk${rootdev}p${rootpart} ${root_rw} rootfstype=ext4 ${opts};run boot_cmd
opts=loglevel=4
partitions=uuid_disk=${uuid_gpt_disk};name=boot,start=1MiB,size=32MiB,uuid=${uuid_gpt_boot};name=modules,size=32MiB,uuid=${uuid_gpt_module};name=rootfs,size=-,uuid=${uuid_gpt_rootfs}
partitions_android=uuid_disk=${uuid_gpt_disk};name=boot,start=1MiB,size=32MiB,uuid=${uuid_gpt_boot};name=system,size=1024MiB,uuid=${uuid_gpt_system};name=cache,size=128MiB,uuid=${uuid_gpt_cache};name=userdata,size=-,uuid=${uuid_gpt_userdata}
ramfsboot=setenv bootargs ${console} root=/dev/mmcblk${rootdev}p${rootpart} ${root_rw} rootfstype=ext4 ${opts} ${recoverymode};run boot_cmd_initrd
recoveryboot=run sdrecovery; setenv recoverymode recovery;run ramfsboot
root_rw=rw
rootdev=0
rootfslen=100000
rootpart=3
sdrecovery=sdfuse format; sdfuse flashall 3
stderr=serial
stdin=serial
stdout=serial
Environment size: 1777/16380 bytes
ARTIK5#
Create/Edit Environment Variable (setenv)
The setenv command changes a value in the current environment, or creates a variable and assigns a value if it does not yet exist.
This example shows changing the log level of the Linux kernel. loglevel will be set to 7 to show more detailed kernel logs.
ARTIK5# setenv opts loglevel=7
Save Environment Variables Permanently (saveenv)
The saveenv command stores the environment variables to the eMMC/SDCard permanently, where they will remain stored even through a system reboot.
ARTIK5# saveenv Saving Environment to MMC... Writing to MMC(0)... done