Fix user switch edge-case (thanks @putnam)

Author: wolveix

init.sh

@@ -2,6 +2,11 @@
 
 set -e
 
+CURRENTUID=$(id -u)
+NUMCHECK='^[0-9]+$'
+RAMAVAILABLE=$(awk '/MemAvailable/ {printf( "%d\n", $2 / 1024000 )}' /proc/meminfo)
+USER="steam"
+
 if [[ "$DEBUG" == "true" ]]; then
     printf "Debugging enabled (the container will exit after printing the debug info)\\n\\nPrinting environment variables:\\n"
     export
@@ -18,17 +23,14 @@ HDD: $(df -h | awk '$NF=="/"{printf "%dGB/%dGB (%s used)\n", $3,$2,$5}')"
     exit 1
 fi
 
-CURRENTUID=$(id -u)
 if [[ "$CURRENTUID" -ne "0" ]]; then
     printf "Current user is not root (%s)\\nPass your user and group to the container using the PGID and PUID environment variables\\nDo not use the --user flag (or user: field in Docker Compose)\\n" "$CURRENTUID"
     exit 1
 fi
 
-ramAvailable=$(awk '/MemAvailable/ {printf( "%d\n", $2 / 1024000 )}' /proc/meminfo)
-printf "Checking available memory...%sGB detected\\n" "$ramAvailable"
-
-if [[ "$ramAvailable" -lt 12 ]]; then
-    printf "You have less than the required 12GB minmum (%sGB detected) of available RAM to run the game server.\\nIt is likely that the server will fail to load properly.\\n" "$ramAvailable"
+printf "Checking available memory...%sGB detected\\n" "$RAMAVAILABLE"
+if [[ "$RAMAVAILABLE" -lt 12 ]]; then
+    printf "You have less than the required 12GB minmum (%sGB detected) of available RAM to run the game server.\\nIt is likely that the server will fail to load properly.\\n" "$RAMAVAILABLE"
 fi
 
 mkdir -p \
@@ -41,8 +43,6 @@ mkdir -p \
     "${GAMESAVESDIR}/server" \
     || exit 1
 
-NUMCHECK='^[0-9]+$'
-
 # check if the user and group IDs have been set
 if ! [[ "$PGID" =~ $NUMCHECK ]] ; then
     printf "Invalid group id given: %s\\n" "$PGID"
@@ -60,7 +60,17 @@ elif [[ "$PUID" -eq 0 ]]; then
     exit 1
 fi
 
-groupmod -g "$PGID" steam
-usermod -u "$PUID" steam
+if [[ $(getent group $PGID | cut -d: -f1) ]]; then
+    usermod -a -G "$PGID" steam
+else
+    groupmod -g "$PGID" steam
+fi
+
+if [[ $(getent passwd ${PUID} | cut -d: -f1) ]]; then
+    USER=$(getent passwd $PUID | cut -d: -f1)
+else
+    usermod -u "$PUID" steam
+fi
+
 chown -R "$PUID":"$PGID" /config /home/steam
-exec gosu steam "/home/steam/run.sh" "$@"
+exec gosu "$USER" "/home/steam/run.sh" "$@"