How to Capture Screenshots over SSH on Debian 12 Wayland Desktops

On legacy Debian 11 (Bullseye) and older X11 desktops, taking a screenshot of an active desktop session remotely over SSH was straightforward using scrot:

DISPLAY=:0.0 scrot -o screenshot.jpg

In Python:

import os
os.environ["DISPLAY"] = ":0.0"
os.system("scrot -o screenshot.jpg")

Wayland on Debian 12 (Bookworm)

On Debian 12 (and Raspberry Pi OS Bookworm with Wayfire or labwc), Wayland is the default compositor. Because Wayland enforces strict security isolation between graphical clients and display sockets, scrot will fail with the error:

failed to create display

To take screenshots under Wayland, use the native grim utility (pre-installed on Raspberry Pi OS). When calling grim over SSH from a non-interactive TTY, you must explicitly export both WAYLAND_DISPLAY and XDG_RUNTIME_DIR:

WAYLAND_DISPLAY=wayland-1 XDG_RUNTIME_DIR=/run/user/1000 grim screenshot.png

Python Automation Script

To capture screenshots programmatically in Python over SSH:

import os

pngfile = "/tmp/screenshot.png"
os.environ["WAYLAND_DISPLAY"] = "wayland-1"
os.environ["XDG_RUNTIME_DIR"] = "/run/user/1000"

os.system(f"grim {pngfile}")

Tip: If you are unsure of your socket names, run echo $WAYLAND_DISPLAY and echo $XDG_RUNTIME_DIR from a terminal inside the active desktop session, or check the socket files in /run/user/$(id -u)/.

How to Set Default Route and Network Metrics on Debian 12 (Bookworm) Using NetworkManager

On Debian 12 (Bookworm) and Raspberry Pi OS Bookworm, dhcpcd has been deprecated and replaced by NetworkManager as the default network management stack. Consequently, /etc/dhcpcd.conf is no longer present.

When multiple network interfaces (such as Ethernet eth0 and Wi-Fi wlan0) are connected simultaneously, the Linux kernel determines the default gateway based on routing metrics. Lower metric values take precedence over higher values.

Rule: Lower route metric = higher routing priority. To prioritize an interface for default internet access, assign it a lower metric than competing interfaces.

1. Inspect Current Routing Metrics

Check the existing routing table and metric values:

ip route show
# or:
route -n

2. List NetworkManager Connection Profiles

Identify the exact connection name you wish to adjust:

nmcli connection show

3. Adjust the Route Metric

You can set the route metric directly using a single nmcli command:

# Set metric to 100 for higher priority (e.g. Ethernet)
nmcli connection modify "Wired connection 1" ipv4.route-metric 100

# Reactivate the connection to apply changes
nmcli connection up "Wired connection 1"

Alternatively, you can edit the connection interactively:

nmcli connection edit "Wired connection 1"
nmcli> set ipv4.route-metric 100
nmcli> save
nmcli> quit

Run ip route show again to verify that your preferred connection now holds the lowest metric on the default route.

How to Configure Eturnal TURN Server with TLS 1.3 and Static Credentials on Debian 12

Eturnal is a modern, lightweight STUN/TURN server written in Erlang that serves as an efficient alternative to Coturn with built-in TLS 1.3 support. While Eturnal natively uses time-limited ephemeral credentials (REST API authentication), many WebRTC clients require static usernames and passwords. Here is how to configure Eturnal on Debian 12 and generate static credentials using an HMAC-SHA1 Python helper.

Stack: Eturnal 1.12+ • Debian 12 Bookworm • TLS 1.3 • HMAC-SHA1 Password Generator

1. Installing Eturnal on Debian 12

# Add Eturnal package repository and install
curl -fsSL https://eturnal.net/gpg.key | sudo gpg --dearmor -o /etc/apt/trusted.gpg.d/eturnal.gpg
echo "deb https://eturnal.net/debian bookworm main" | sudo tee /etc/apt/sources.list.d/eturnal.list
sudo apt-get update && sudo apt-get install eturnal -y

2. Generating Static TURN Credentials via Python

To produce valid credentials matching your configured shared secret (secret: "YOUR_SHARED_SECRET" in /etc/eturnal.yml):

import time
import hmac
import hashlib
import base64

SHARED_SECRET = "YOUR_SHARED_SECRET"
# Set expiration timestamp (e.g. 1 year in the future)
expiry = int(time.time()) + (365 * 24 * 3600)
username = f"{expiry}:user1"

# Compute HMAC-SHA1 hash
key = SHARED_SECRET.encode('utf-8')
msg = username.encode('utf-8')
password = base64.b64encode(hmac.new(key, msg, hashlib.sha1).digest()).decode('utf-8')

print(f"TURN Username: {username}")
print(f"TURN Password: {password}")

How to Compile and Install Coturn 4.6.2 with TLS 1.3 Support on Debian 12 (Bookworm)

Coturn is the standard open-source STUN/TURN server enabling WebRTC audio/video connections across symmetric NATs and firewalls. Full support for modern TLS 1.3 encrypted TURN connections (TURNS) was added in Coturn 4.6.2. Because Debian 12 (Bookworm) originally packaged Coturn 4.6.1, compiling version 4.6.2 from source with OpenSSL 3.x is necessary for enterprise TLS 1.3 compliance.

Features: TURNS over TLS 1.3 • WebRTC relay performance • Debian 12 Bookworm

Compilation & Installation Commands

# 1. Install build tools and OpenSSL 3 development libraries
sudo apt-get update
sudo apt-get install -y pkg-config build-essential libssl-dev libevent-dev git

# 2. Download Coturn 4.6.2 release
cd /usr/src
git clone https://github.com/coturn/coturn.git
cd coturn
git checkout 4.6.2

# 3. Configure and compile with OpenSSL
./configure --prefix=/usr/local
make -j$(nproc)
sudo make install

# Verify binary and TLS support
turnserver -v

How to Suppress OpenCV and GStreamer nvarguscamerasrc (GST_ARGUS) Debug Logs on NVIDIA Jetson

When capturing MIPI CSI camera video on NVIDIA Jetson Nano, Xavier, or Orin platforms using OpenCV with GStreamer's nvarguscamerasrc plugin, the driver constantly spams stdout and stderr with verbose hardcoded debug strings (such as GST_ARGUS: Creating output stream and CONSUMER: Waiting until producer is connected...).

Why Log Levels Don't Work: These prints are hardcoded inside NVIDIA's gstnvarguscamerasrc.cpp C++ source code via printf(), bypassing standard GStreamer debug level filters (GST_DEBUG=0).

1. Rebuilding nvarguscamerasrc Without Hardcoded Prints

Download your matching JetPack BSP public sources and remove the hardcoded print macros:

# Check active L4T release
cat /etc/nv_tegra_release

# Extract gst-nvarguscamera source
cd ~/src/Linux_for_Tegra/source/public
tar -jxvf gst-nvarguscamera_src.tbz2
cd gst-nvarguscamera/

# Edit gstnvarguscamerasrc.cpp and empty out the print macros:
sed -i 's/#define GST_ARGUS_PRINT(...) printf(__VA_ARGS__)/#define GST_ARGUS_PRINT(...)/g' gstnvarguscamerasrc.cpp
sed -i 's/#define CONSUMER_PRINT(...) printf(__VA_ARGS__)/#define CONSUMER_PRINT(...)/g' gstnvarguscamerasrc.cpp

# Compile and install plugin
make
sudo make install

2. Suppressing OpenCV Warnings in Python

In your Python application, silence OpenCV library logs and restart the camera daemon prior to acquisition:

import os
import warnings

# Suppress Python warnings & OpenCV internal logging
warnings.filterwarnings('ignore')
os.environ["OPENCV_LOG_LEVEL"] = "OFF"

# Restart camera daemon to ensure clean hardware state
os.system("sudo systemctl restart nvargus-daemon")

Your camera capture scripts will now run silently without terminal clutter.

How to Install Asterisk 18 and FreePBX 16 on Raspberry Pi OS Bullseye (64-bit & 32-bit)

Deploying Asterisk 18 LTS alongside the modern FreePBX 16 administrative interface on Raspberry Pi OS (Debian 11 Bullseye) enables a carrier-grade VoIP telephony platform on energy-efficient ARM hardware. This guide provides the complete setup for both 64-bit (aarch64) and 32-bit (armhf) architectures.

OS: Raspberry Pi OS Bullseye • Components: Asterisk 18.x, FreePBX 16, Node.js 14, MariaDB 10.5, Apache 2.4

1. Installing System Packages & PHP 7.4

sudo apt-get update && sudo apt-get upgrade -y
sudo apt-get install -y build-essential libssl-dev libncurses5-dev libnewt-dev   libxml2-dev libsqlite3-dev uuid-dev mariadb-server mariadb-client   libjansson-dev libedit-dev sox libsox-fmt-all git curl subversion

# Install PHP 7.4 modules required by FreePBX 16
sudo apt-get install -y apache2 php php-cli php-mysql php-pear php-gd php-mbstring   php-intl php-xml php-curl php-zip

2. Building Asterisk 18 LTS

cd /usr/src
sudo wget http://downloads.asterisk.org/pub/telephony/asterisk/asterisk-18-current.tar.gz
sudo tar -zxf asterisk-18-current.tar.gz
cd asterisk-18.*

sudo contrib/scripts/get_mp3_source.sh
sudo contrib/scripts/install_prereq install

sudo ./configure --with-pjproject-bundled --with-jansson-bundled
sudo make menuselect.makeopts
sudo menuselect/menuselect --enable format_mp3 menuselect.makeopts
sudo make -j$(nproc)
sudo make install
sudo make config
sudo ldconfig

3. Installing FreePBX 16

cd /usr/src
sudo wget http://mirror.freepbx.org/modules/packages/freepbx/freepbx-16.0-latest.tgz
sudo tar -zxf freepbx-16.0-latest.tgz
cd freepbx
sudo ./install -n

How to Set Up a Samba Network Storage Drive on Raspberry Pi for Hikvision IP Cameras

Hikvision value IP cameras (such as the IPC-B120, IPC-B121H, and IPC-B120-D-W) feature onboard motion detection, infrared night vision, and H.265+ compression, but lack internal hard drives. Rather than purchasing an expensive commercial NVR, you can attach an external USB hard disk to a Raspberry Pi configured as an SMB/CIFS Network Attached Storage (NAS) target for continuous or motion-triggered video archiving.

Stack: Raspberry Pi 4 • External USB HDD (ext4) • Samba Server (SMBv2/v3) • Hikvision Storage Management

1. Installing and Configuring Samba on the Raspberry Pi

sudo apt-get update
sudo apt-get install samba samba-common-bin -y

# Create recording directory on mounted external drive
sudo mkdir -p /media/cctv_storage/hikvision
sudo chown -R nobody:nogroup /media/cctv_storage/hikvision
sudo chmod -R 0777 /media/cctv_storage/hikvision

2. Samba Share Definition (/etc/samba/smb.conf)

Hikvision firmware requires specific Samba dialect and locking settings to format network drives successfully:

[hikvision]
   comment = Hikvision CCTV Storage
   path = /media/cctv_storage/hikvision
   browseable = yes
   writeable = yes
   guest ok = yes
   read only = no
   create mask = 0777
   directory mask = 0777
   force user = nobody

Restart Samba:

sudo systemctl restart smbd

3. Mounting the Drive in Hikvision Web GUI

1. Log into your camera's web interface → Configuration → Storage → Storage Management → Net HDD.
2. Set Type to NAS / SMB/CIFS, enter the Raspberry Pi's IP address, set File Path to /hikvision, and save.
3. Under HDD Management, select the newly added network disk and click Format / Init. Once status changes to Normal, motion recordings will save directly to your Pi.