Frequently Asked Questions (FAQ)

Failed to Open Serial Port Device

If you encounter the error Error: Permission denied, cannot open /dev/ttyUSB0 when trying to open the serial port!

You can troubleshoot the issue by following these steps:

1. Check if the serial device is properly connected to the PC

2. Check serial device permissions

For Linux systems, if the serial device has insufficient permissions, you need to run the following commands in the terminal to grant the current user access to the device.

• View serial device information

Using /dev/ttyUSB0 as an example:

Linux$

ls -l /dev/ttyUSB0

If the device exists on the system, you will see output similar to:

crw-rw---- 1 root dialout 188, 0 Sep 10 21:24 /dev/ttyUSB0

• Add current user to the dialout group

Linux$

sudo usermod -a -G dialout $USER

• Log in again

Linux$

newgrp dialout

3. Check if the serial device is being used by another program

Why does Radxa OS use GDM by default instead of SDDM?

Radxa OS uses GDM (GNOME Display Manager) instead of SDDM (Simple Desktop Display Manager) by default for the following reasons:

SDDM Limitations:

• SDDM cannot properly start the graphical interface in headless mode when HDMI is not connected
• This prevents users from logging in through remote desktop or VNC

GDM Advantages:

• Runs stably in various connection states (including headless mode)
• Provides better compatibility and reliability

If you want to switch back to SDDM, follow these steps:

Linux$

sudo dpkg-reconfigure sddm

In the configuration interface that appears, select sddm as the default display manager, then restart the system for the changes to take effect.

why my SBC cannot connect Wi-Fi when it is only logged in to the desktop mode?

Because KDE or GNOME desktop environment stores Wi-Fi passwords in the user-specific keyring by default. The keyring will only be unlocked when the user logs in to the graphical interface, which means that the system cannot automatically connect to a protected Wi-Fi network when it is not logged in (such as in headless mode), and SSH cannot be used. To solve this problem, you can choose one of the following three methods:

• Enable automatic login: This will allow the system to automatically log in to the specified user, unlocking the keyring, allowing Wi-Fi connection. Use the rsetup tool to enable automatic login.
• Disable keyring encryption: You can disable keyring encryption by following these steps: KDE Settings -> KDE Wallet -> Disable keyring encryption. Then forget the Wi-Fi password and reconnect to the Wi-Fi. This way, the keyring will no longer be encrypted, and the system can access the Wi-Fi password without user login, enabling automatic connection to Wi-Fi networks. Please note that this method reduces system security.
• Use nmtui/nmcli tools to manually add Wi-Fi password: Use command-line tools nmtui or nmcli to manually configure Wi-Fi network connections and save the password to system-wide configuration files instead of the user's keyring.

Linux$

nmcli connection add type wifi con-name <connection_name> ssid <ssid> password <password>
# or
nmtui

Network Connection Automatically Disconnects

You can modify the parameters in the /usr/share/glib-2.0/schemas/org.gnome.settings-daemon.plugins.power.gschema.xml file to disable sleep timeout.

radxa@dragon-q6a$

vim /usr/share/glib-2.0/schemas/org.gnome.settings-daemon.plugins.power.gschema.xml

Modify the sleep-inactive-ac-timeout and sleep-inactive-battery-timeout parameters in the file to have a default value of 0, then restart the system for the changes to take effect.

Why does Q6A reboot immediately when using the hardware encoder?

Before using the hardware encoder, you need to enable the following option in BIOS:

Hypervisor Settings -> Hypervisor Override in UEFI Setup

You can enter UEFI Setup by pressing F2 during boot.

If this option is not enabled, calling the hardware encoder may cause the system to reboot immediately.

After enabling the hardware encoder, the following changes apply:

• The system boots in EL2 instead of EL1, and KVM can be used
• /dev/mtd0 disappears, so you cannot update the SPI firmware directly on the board

Why does the system fail to boot after running sudo apt upgrade?

Running sudo apt upgrade to upgrade the system may cause incomplete updates or system abnormalities (such as failure to boot). It is recommended to use the Rsetup tool for system updates:

radxa@dragon-q6a$

sudo rsetup

In Rsetup, select System -> System Update to complete the update.

For more details, please refer to: System Update.

warning

If the power is interrupted or the update fails during the process, the system may fail to boot normally. In this case, you need to re-flash the system image.

How to Fix 7-inch Display Garbled Screen Issue?

The 7-inch display defaults to 1080p resolution. If the display does not support this resolution, it will cause a garbled screen, and you need to manually set the correct screen resolution.

Check Supported Resolutions

First, connect the display and log into the system, then check the HDMI output supported resolutions:

radxa@dragon-q6a$

# Parse EDID content (edid-decode needs to be installed)
sudo apt install edid-decode
sudo edid-decode /sys/class/drm/card1-HDMI-A-1/edid

Check the output to confirm the list of supported resolutions. If the 7-inch display's 1024x600 resolution does not appear in the default modes list, it means the default 1080p resolution setting is causing the display issue.

Adjust Resolution

After confirming the resolution, modify the kernel command line parameters to specify the correct screen resolution:

radxa@dragon-q6a$

old=$(cat /etc/kernel/cmdline)
echo "$old video=HDMI-A-1:1024x600@60" | sudo tee /etc/kernel/cmdline

Update Kernel

radxa@dragon-q6a$

sudo kernel-install add $(uname -r) /boot/vmlinuz-$(uname -r)

Reboot

radxa@dragon-q6a$

sudo reboot

If the display is still abnormal after rebooting, please reconnect the HDMI cable.