Use static paths so we can use the exec form of CMD

Dockerfile

@@ -5,30 +5,28 @@ MAINTAINER Chris Kankiewicz <Chris@ChrisKankiewicz.com>
 ENV MUMBLE_VERSION 1.2.12
 
 # Create Mumble directories
-ENV MUMBLE_DIR  /opt/mumble
-ENV CONFIG_DIR  /srv/mumble
-RUN mkdir -pv ${MUMBLE_DIR} ${CONFIG_DIR}
+RUN mkdir -pv /opt/mumble /etc/mumble
 
 # Copy config file
-COPY files/config.ini ${CONFIG_DIR}/config.ini
+COPY files/config.ini /etc/mumble/config.ini
 
 # Copy SuperUser password update script
 COPY files/supw /bin/supw
 RUN chmod +x /bin/supw
 
-# Set the zipball URL
+# Set the bzip archive URL
 ENV BZIP_URL https://github.com/mumble-voip/mumble/releases/download/${MUMBLE_VERSION}/murmur-static_x86-${MUMBLE_VERSION}.tar.bz2
 
 # Install dependencies and fetch Mumble bzip archive
 RUN apk add --update ca-certificates bzip2 tar wget \
-    && wget -qO- ${BZIP_URL} | tar -xjv --strip-components=1 -C ${MUMBLE_DIR} \
+    && wget -qO- ${BZIP_URL} | tar -xjv --strip-components=1 -C /opt/mumble \
     && apk del ca-certificates bzip2 tar wget && rm -rf /var/cache/apk/*
 
 # Expose ports
 EXPOSE 64738 64738/udp
 
 # Set volumes
-VOLUME ${CONFIG_DIR}
+VOLUME /etc/mumble
 
 # Default command
-CMD ${MUMBLE_DIR}/murmur.x86 -fg -ini ${CONFIG_DIR}/config.ini
+CMD ["/opt/mumble/murmur.x86", "-fg", "-ini", "/etc/mumble/config.ini"]

files/config.ini

@@ -3,4 +3,4 @@
 
 # Path to database. If blank, will search for
 # murmur.sqlite in default locations or create it if not found.
-database=/srv/mumble/murmur.sqlite
+database=/etc/mumble/murmur.sqlite

files/supw

@@ -1,3 +1,3 @@
 #!/usr/bin/env sh
 
-${MUMBLE_DIR}/murmur.x86 -ini ${CONFIG_DIR}/config.ini -readsupw
+/opt/mumble/murmur.x86/murmur.x86 -ini /etc/mumble/config.ini -readsupw