This documentation will introduce how to use the configuration file of the Ubuntu system.

With kernel 4.9, env.txt is located in the /boot directory and is an environment configuration file used to configure the functions of the Ubuntu system. The system will read this file when it starts to set HDMI, fan, CPU frequency, etc.

With kernel 5.15, uEnv.txt is located in the /boot directory and is an environment configuration file used to configure the user bootargs.

If not mentioned, the configuration applies for both 4.9 and 5.15 Kernel.

The default setting is yes, it will automatically detect HDMI and set the best resolution, if it is set to no, you can set it manually:

# HDMI resolution auto detection
# yes - auto detection
# no  - set HDMI resolution via 'hdmi' node
hdmi_autodetect=yes

Disable auto detect:

hdmi_autodetect=no

In some situations HDMI resolution auto detect will not work, and you can try to setup the HDMI resolution manually.

Only when hdmi_autodetect=no, the changed configuration will take effect, the default is 720p.

Set to 1080p:

hdmi=1080p60hz

Save the file and reboot to take effect.

• off : Cooling fan is disabled.
• low : Cooling fan is working at low speed mode.
• mid : Cooling fan is working at middle speed mode.
• high : Cooling fan is working at high speed mode.
• auto : Cooling fan is working at auto speed mode. By default, the fan speed is determined by CPU temperature.

Set fan level to high:

fan_mode=high

Save the file and reboot to take effect.

khadas@Khadas:~$ cat /boot/env.txt | grep "fb_rotate"
fb_rotate=0

Rotate 90 degrees:

fb_rotate=1

Save the file and reboot to take effect.

$ cat /proc/cmdline

You can edit file /boot/uEnv.txt to add the user bootargs.

The default file contents are similar as below:

$ cat /boot/uEnv.txt 
#############################DO NOT TOUCH THIS OPTION#############################
rootdev=root=UUID=a92f7f2f-0d4a-4607-a45a-4549cfe71036
partitiontype=partition_type=generic
#############################DO NOT TOUCH THIS OPTION#############################
## Setup console
consoles=console=ttyS0,115200 console=tty0
 
## Setup FAN mode
fan_mode=auto
 
## Add user args here, spilt with space.
## e.g. Add bootargs 'test1=111 test2=222'
## boot_user_args=test1=111 test2=222
boot_user_args=

You can append your bootargs to the configuration boot_user_args=.

e.g. Add bootargs cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory systemd.unified_cgroup_hierarchy=0, the variable boot_user_args= should be as below:

boot_user_args=cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory systemd.unified_cgroup_hierarchy=0

You can change the linux UART pins for normal usage by modifying the configuration console=

eg. Enable linux UART console should be as below:

consoles=console=ttyS0,115200 console=tty0

Save the file and reboot to take effect.

After edit the file, you need to save the file and reboot the board.

khadas@Khadas:~$ sync
khadas@Khadas:~$ sudo reboot