When trying to daemonize a Windows application running under Wine on Linux, you might encounter issues with environment variables - particularly $DISPLAY for X11 applications. The standard approach of prefixing the command with variables (VAR=value start-stop-daemon) fails when using the -c user option because the environment gets reset.

The -c user switch in start-stop-daemon creates a clean environment for security reasons. This means:

• Variables set before the command are ignored
• User's .bashrc or .profile aren't sourced
• System-wide environment files aren't read

Here are several approaches that actually work:

1. Using envfile with start-stop-daemon

Some versions support the --env-file option:

start-stop-daemon --start \
  --pidfile /var/run/wine-app.pid \
  -m -c myuser -g mygroup \
  --env-file /path/to/envfile \
  --exec /home/myuser/.wine/drive_c/Program\ Files/wine-app.exe

Create the envfile with your variables:

DISPLAY=:0
WINEPREFIX=/home/myuser/.wine

2. Wrapper Script Approach

Create a wrapper script that sets the environment:

#!/bin/bash
export DISPLAY=:0
export WINEPREFIX=/home/myuser/.wine
exec /home/myuser/.wine/drive_c/Program\ Files/wine-app.exe "$@"

Then point start-stop-daemon to the wrapper:

start-stop-daemon --start \
  --pidfile /var/run/wine-app.pid \
  -m -c myuser -g mygroup \
  --exec /path/to/wrapper-script.sh

3. Systemd Alternative (for modern systems)

If you're on a system with systemd, create a service file:

[Unit]
Description=Wine Application
After=network.target

[Service]
User=myuser
Group=mygroup
Environment="DISPLAY=:0"
Environment="WINEPREFIX=/home/myuser/.wine"
ExecStart=/home/myuser/.wine/drive_c/Program\ Files/wine-app.exe
Restart=on-failure

[Install]
WantedBy=multi-user.target

• Ensure the X11 server is running before starting your Wine app
• Check permissions on /var/run for PID file creation
• Consider using xvfb-run for headless environments
• Test environment variables with env in your wrapper script

If you're still having issues:

# Check what environment the process actually sees:
start-stop-daemon --start \
  --pidfile /tmp/debug.pid \
  -m -c myuser \
  --exec /usr/bin/env > /tmp/wine-env.log

# Check X11 access:
sudo -u myuser xhost

Remember that Wine applications often need additional environment variables like WINEDEBUG, WINEPREFIX, or WINEARCH set properly.

---

When trying to daemonize Windows applications running under Wine that require X11 display access, we often hit a wall with environment variable inheritance. The traditional approach of prefixing commands with variables like DISPLAY=:0 fails when combined with start-stop-daemon's user switching (-c option).

Many users first attempt to set DISPLAY in the target user's shell configuration files, but this fails because:

• start-stop-daemon doesn't spawn a login shell
• The daemon environment is sanitized for security
• X11 session variables exist in a specific session context

Method 1: Using envfile (Recommended)

Create an environment file and source it before execution:

# /etc/default/wine-app
DISPLAY=:0
XAUTHORITY=/home/myuser/.Xauthority

# In init script
start-stop-daemon --start \
    --pidfile /var/run/wine-app.pid \
    -m -c myuser -g mygroup \
    --env-file /etc/default/wine-app \
    --exec /usr/bin/env -- \
    /home/myuser/.wine/drive_c/Program\ Files/wine-app.exe

Method 2: Wrapper Script Approach

Create a wrapper that sets the environment:

#!/bin/bash
# /usr/local/bin/wine-app-wrapper
export DISPLAY=:0
export XAUTHORITY=/home/myuser/.Xauthority
exec /home/myuser/.wine/drive_c/Program\ Files/wine-app.exe "$@"

# Then call the wrapper
start-stop-daemon --start \
    --pidfile /var/run/wine-app.pid \
    -m -c myuser -g mygroup \
    --exec /usr/local/bin/wine-app-wrapper

Method 3: Direct env Injection (For Modern Systems)

Newer start-stop-daemon versions support direct env setting:

start-stop-daemon --start \
    --pidfile /var/run/wine-app.pid \
    -m -c myuser -g mygroup \
    --env DISPLAY=:0 \
    --env XAUTHORITY=/home/myuser/.Xauthority \
    --exec /home/myuser/.wine/drive_c/Program\ Files/wine-app.exe

• Always validate the Xauthority file permissions
• Consider using xhost restrictions instead of :0
• The wrapper script should be root-owned with 755 permissions

If you still experience issues:

1. Verify the X11 socket exists: ls -l /tmp/.X11-unix/
2. Check process environment: cat /proc/$(pidof wine-app.exe)/environ | tr '\\0' '\\n'
3. Test without daemonization first: sudo -u myuser env DISPLAY=:0 wine-app.exe