Entrypoint

The dde entrypoint (resources/entrypoint.sh) is a POSIX shell script that runs as the container’s entrypoint. It prepares the container environment for development and then hands off to the original command.

Execution Flow

1. Ensure dde User Exists

The entrypoint creates a dde user and group matching the host UID/GID (passed via DDE_UID and DDE_GID environment variables, defaulting to 1000).

Because the entrypoint runs on arbitrary base images, it first detects which user/group tooling the image ships, then fires exactly one command for that dialect:

1. shadow (useradd/groupadd) — preferred when present (Debian, and Alpine once shadow is installed); flags are identical on every distro.
2. busybox (adduser -u -G -D / addgroup -g) — base Alpine.
3. debian (adduser --uid --ingroup --disabled-password / addgroup --gid) — Debian’s Perl adduser when useradd is absent.
4. Manual /etc/passwd — genuine last resort when no usable tool exists or the tool fails.

The dialect is resolved once into a DIALECT variable. adduser/addgroup is the same command name for two incompatible programs (BusyBox’s C binary vs Debian’s Perl script), and both exit 0 on --help, so the only reliable discriminator is adduser --help 2>&1 | grep -qi busybox. Feeding BusyBox short flags to Debian’s adduser makes it abort with an “Option is ambiguous” usage dump and leaves the user uncreated — the regression that flooded a WordPress container’s log and forced the raw /etc/passwd fallback on every start.

Group creation is skipped when DDE_GID is already taken; the user then joins that existing group (resolved via getent group "$DDE_GID") instead of colliding on the GID. On failure each branch emits a single dde-entrypoint: warning: ... line to stderr — loud enough to diagnose, never fatal, so images that ran fine before dde injected the entrypoint keep starting.

2. UID/GID Remapping

If the dde user already exists (e.g. from the dev layer) but has a different UID/GID than requested:

1. usermod/groupmod — preferred method for remapping
2. sed on /etc/passwd — fallback if usermod is not available
3. chown home directory — updates ownership of /home/dde

3. Shell Detection

The user’s shell is set based on the following priority:

1. DDE_SHELL environment variable (if set, uses /bin/$DDE_SHELL)
2. /bin/zsh (if available)
3. /bin/bash (if available)
4. /bin/sh (fallback)

The detected shell is set as the login shell for the dde user via usermod -s or direct /etc/passwd editing.

4. Run Built-in Adapters

Scripts in /dde/adapters/ (mounted from resources/adapters/) are sourced and executed:

for adapter in "$DDE_ADAPTERS_DIR"/*.sh; do
    [ -f "$adapter" ] || continue
    . "$adapter"
    if type detect >/dev/null 2>&1 && detect; then
        configure || true
    fi
    unset -f detect configure 2>/dev/null || true
done

Each adapter script must define detect() and configure() functions. If detect() returns 0 (success), configure() is called. Functions are unset after each adapter to prevent conflicts.

Built-in adapters: nginx.sh, php-fpm.sh, apache.sh.

5. Run Project Adapters

Scripts in /dde/adapters-project/ (mounted from .dde/adapters/) are processed identically to built-in adapters. This allows projects to add custom setup logic.

6. Exec Original Command

exec "$@"

The arguments passed to the entrypoint ($@) are the original entrypoint and CMD from the Docker image. The compose override sets these as the command arguments, so exec "$@" chains to the original startup sequence.

Environment Variables

Variable	Default	Description
DDE_UID	1000	User ID for the dde user
DDE_GID	1000	Group ID for the dde user
DDE_SHELL	(unset)	Override shell detection (e.g. bash, zsh)
DDE_ADAPTERS_DIR	/dde/adapters	Path to built-in adapter scripts

Key Design Decisions

• POSIX sh: The script uses /bin/sh (not bash) for maximum compatibility across Alpine, Debian, and other base images.
• Idempotent: Safe to run multiple times (uses || true for operations that may already be done).
• Non-destructive: If user creation fails for any reason, the container still starts with the original CMD.
• exec replaces shell: Using exec "$@" ensures the original process becomes PID 1, receiving signals correctly.