System issue

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Does the system have a default username and password?

No default credentials are provided. When Debian starts for the first time, you must create a user account. Keep a record of the username and password, as these credentials are required for future logins.

How do I enable a Chinese input method?

Follow these steps to install and configure a Chinese input method:

# 1. Install
sudo apt install ibus ibus-libpinyin fonts-noto-cjk -y

# 2. Check the current configuration
gsettings get org.gnome.desktop.input-sources sources

# 3. Configure the input sources
gsettings set org.gnome.desktop.input-sources sources "[('xkb', 'us'), ('ibus', 'libpinyin')]"

# 4. Restart the system
reboot

# 5. Switch input methods. Super is the Windows logo key
Super + Space

How do I check the current system status?

# Monitor CPU activity in real time
top

# View currently running and waiting processes
ps aux | grep <comm>

# View overall memory and swap usage
free -h

# View disk partition usage
df -h

How do I check the system version?

# Check the build version
cat /etc/quectel-release

# Check the kernel version
uname -a

How do I upgrade the system?

sudo apt update
sudo apt upgrade

Note

  1. If the system fails to start properly, reflash the system mirror.

  2. Visit the Firmware download center to obtain the latest firmware release.

  3. For instructions on flashing the system mirror, see System installation.

What should I do if packages cannot be downloaded?

Check the network connection and proxy settings

  • Network connectivity: First, make sure the device is connected to the network. Run ping -c 4 8.8.8.8 or ping -c 4 archive.ubuntu.com to test network connectivity. If neither command succeeds, check the Ethernet cable, Wi-Fi connection, or IP address configuration.

  • Proxy server: If a proxy is configured, verify its settings or temporarily disable it. Check /etc/apt/apt.conf.d/ for proxy configuration files such as proxy.conf, and temporarily rename the relevant file if necessary.

Check and update the package repositories

Incorrect repository configuration is a common cause of download failures.

  • View the current repositories: Run cat /etc/apt/sources.list and ls -l /etc/apt/sources.list.d/, and check for invalid or outdated repository URLs.

  • Change the mirror: If the default repositories are unstable or slow, switch to a reliable mirror in China, such as one provided by Tsinghua University, Alibaba Cloud, or the University of Science and Technology of China. After changing the mirror, run sudo apt update to apply the change. For details, see Software update.

  • Back up the repository configuration: Before making changes, run sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak to create a backup.

Update package lists and repair dependencies

Outdated package lists or broken dependencies can cause download failures.

  • Update the package list: This is an essential step. Run sudo apt update to ensure that the system can retrieve the latest package information.

  • Repair dependencies: If the issue persists after the update, try running sudo apt –fix-broken install to repair broken dependencies.

  • Use the –fix-missing option: If you encounter an Unable to fetch some archives error, try running sudo apt update –fix-missing.

Check disk space and package manager processes

Insufficient disk space or another running package-management process can also cause download failures.

  • Check disk space: Run df -h to check the available space on the root (/) and /var partitions. If space is low, run sudo apt clean to clear the APT cache, and run sudo apt autoremove to remove unnecessary packages.

  • Check package manager processes: If another APT or dpkg process is running, run ps aux | grep -E “apt|dpkg” to view it. Wait for the process to finish, or run sudo kill -9 <process_ID> to forcefully terminate it. If it cannot be terminated, run sudo rm /var/lib/apt/lists/lock to try to remove the lock file.

Check other possible causes

  • Verify the package name: APT cannot locate a package if its name is misspelled. Run apt-cache search <keyword> to identify the correct package name.

  • Import the GPG key: If a GPG error appears during an update, a key may be missing. Run sudo apt-key adv –keyserver keyserver.ubuntu.com –recv-keys <missing_key_ID> to import it.

  • Check the system time: An incorrect system time can cause HTTPS certificate verification to fail. Run date to check the time. If the time is incorrect, run sudo timedatectl set-ntp true to synchronize it.

  • If the package is unavailable from the configured repositories, download the .deb package and run sudo dpkg -i xxx.deb to install it locally.

How do I troubleshoot high memory usage?

Confirm that the system is actually low on memory

free -h
cat /proc/meminfo | head -30

Pay particular attention to these fields:

MemAvailable
SwapFree
Cached
Buffers
Slab
SReclaimable
SUnreclaim

Use the following criteria:

  • A high used value does not necessarily indicate a problem because Linux uses free memory for the page cache.

  • The key is to check whether MemAvailable is too low.

  • The system is under genuine memory pressure only when MemAvailable is low, swap usage continues to increase, and the system becomes sluggish.

Check for OOM events or memory warnings

dmesg -T | grep -i -E "oom|out of memory|killed process|memory allocation failure"
journalctl -k | grep -i -E "oom|out of memory|killed process"

If the following log messages appear, the system has experienced an out-of-memory (OOM) condition.

Out of memory
Killed process xxx

Identify the processes using the most memory

ps aux --sort=-rss | head -20

Or:

ps -eo pid,ppid,comm,rss,vsz,%mem --sort=-rss | head -30

The fields are defined as follows:

Field

Meaning

RSS

Physical memory actually in use.

VSZ

Virtual address space, not actual memory usage.

%MEM

Percentage of total memory.

You can also use:

top

After the interface opens, press M to sort processes by memory usage.

M

View detailed memory information for a process

Assume that the process ID (PID) is 1234:

cat /proc/1234/status | grep -E "VmRSS|VmSize|VmData|VmSwap|Threads"

For more detailed information:

cat /proc/1234/smaps_rollup

Pay particular attention to these fields:

Rss
Pss
Private_Clean
Private_Dirty
Swap

If Private_Dirty continues to increase, it usually indicates a memory leak.

What should I do if the system freezes?

Determine the severity of the system freeze by checking whether the keyboard, network, or serial port still responds.

  • Responsive (soft lockup): For example, SSH remains accessible, the serial port still accepts input, or the SysRq key still works. This indicates that the kernel is still running but one or more processes are unresponsive. Diagnose the issue before attempting a forced restart to avoid losing diagnostic information.

  • Completely unresponsive (hard lockup): The keyboard indicators do not flash, the network connection is completely lost, and the serial port produces no output. This condition is typically caused by a kernel panic, a hardware lockup, or a fatal interrupt storm. Recovery requires a hardware reset or power cycle.