Support PUID and PGID vars to set runtime user and group ids

Dockerfile

@@ -2,11 +2,17 @@ FROM alpine:3
 
 ARG TARGETPLATFORM
 
+VOLUME /backups
+
 RUN apk add --no-cache libc6-compat
 
 ADD ${TARGETPLATFORM}/git-backup /
 RUN chmod +x /git-backup
 
-VOLUME /backups
+## Add the user for command execution
+RUN apk add --no-cache shadow
+
+ADD ./docker-entrypoint.sh /docker-entrypoint.sh
+RUN chmod +x /docker-entrypoint.sh
 
-ENTRYPOINT ["/git-backup", "-backup.path", "/backups", "-config.file", "/backups/git-backup.yml"]
+ENTRYPOINT ["/docker-entrypoint.sh", "-backup.path", "/backups", "-config.file", "/backups/git-backup.yml"]

README.md

@@ -91,5 +91,16 @@ First, create your [git-backup.yml file](#configuration-file) at `/path/to/your/
 Then update your backups using the mounted volume.
 
 ```bash
-docker run --volume /path/to/backups:/backups ghcr.io/chappio/git-backup:latest
+docker run -v /path/to/backups:/backups ghcr.io/chappio/git-backup:1
 ```
+
+### Parameters
+
+You can specify several parameters when starting this container.
+
+| **Parameter**                  | **Description**                                                                        |
+|--------------------------------|----------------------------------------------------------------------------------------|
+| `-v /path/to/backups:/backups` | Mount the folder where you want to store your backups and read you configuration file. |
+| `-e TZ=Europe/Amsterdam`       | Set the timezone used for logging.                                                     |
+| `-e PUID=0`                    | Set the user id of the unix user who will own the backup files in /backup.             |
+| `-e PGID=0`                    | Set the group id of the unix user's group who will own the backup files.               | 

docker-entrypoint.sh

@@ -0,0 +1,22 @@
+#!/bin/sh
+set -eu
+if [[ -z "${PUID-}" && -z "${PGID-}" ]]
+then
+  # We are running through normal docker user changes, so nothing special to do
+  /git-backup "$@"
+else
+  # We are running with an environment variable user change
+  PUID=${PUID:-$(id -u)}
+  PGID=${PGID:-$(id -g)}
+
+  # Make sure the user exists
+  useradd -o -u "$PUID" -U -d /backups -s /bin/false git-backup
+  groupmod -o -g "$PGID" git-backup
+
+  # Own the backups folder
+  chown git-backup:git-backup /backups
+
+  # Let's go!
+  echo /git-backup "$@" | su -s /bin/sh git-backup
+fi
+