Implement a "runas.sh" utility script for fixing ownership

runas.sh

@@ -0,0 +1,83 @@
+#!/bin/bash
+
+USER=docker
+GROUP=docker
+
+#-----------------------------------------------------------------------------------------------------------------------
+
+function ts {
+  echo [`date '+%b %d %X'`]
+}
+
+#-----------------------------------------------------------------------------------------------------------------------
+
+function update_users {
+  local UMAP=$1
+
+  if [[ "$UMAP" == "" ]]; then return; fi
+
+  echo "$(ts) Updating existing users..."
+
+  for NAME_UID_GID in $UMAP
+  do
+    local NAME=${NAME_UID_GID%:*:*}
+    local USER_ID=${NAME_UID_GID#*:}
+    USER_ID=${USER_ID%:*}
+    local GROUP_ID=${NAME_UID_GID#*:*:}
+
+    echo "$(ts) Setting user \"$NAME\" to user ID=\"$USER_ID\" and default group ID=\"$GROUP_ID\""
+    usermod -o -u $USER_ID -g $GROUP_ID $NAME
+  done
+}
+
+#-----------------------------------------------------------------------------------------------------------------------
+
+function update_groups {
+  local GMAP=$1
+
+  if [[ "$GMAP" == "" ]]; then return; fi
+
+  echo "$(ts) Updating existing groups..."
+
+  for NAME_GID in $GMAP
+  do
+    local NAME=${NAME_GID%:*}
+    local GROUP_ID=${NAME_GID#*:}
+
+    echo "$(ts) Setting group \"$NAME\" to ID=\"$GROUP_ID\""
+    groupmod -o -g $GROUP_ID $NAME
+  done
+}
+
+#-----------------------------------------------------------------------------------------------------------------------
+
+function create_user {
+  local UID_GID=$1
+
+  # Create a new user with the proper user and group ID.
+  local USER_ID=${UID_GID%:*}
+  local GROUP_ID=${UID_GID#*:}
+
+  echo "$(ts) Creating user \"$USER\" (ID $USER_ID) and group \"$GROUP\" (ID $GROUP_ID) to run the command..."
+
+  # We could be aliasing this new user to some existing user. Let's assume that's harmless.
+  groupadd -o -g $GROUP_ID $GROUP
+  useradd -o -u $USER_ID -r -g $GROUP -s /sbin/nologin -c "Docker image user" $USER
+}
+
+#-----------------------------------------------------------------------------------------------------------------------
+
+# Shift off the args as we go so that we can exec $@
+UMAP=$1
+shift
+GMAP=$1
+shift
+UID_GID=$1
+shift
+
+update_users "$UMAP"
+update_groups "$GMAP"
+create_user "$UID_GID"
+
+echo "$(ts) Running command as user \"$USER\"..."
+exec /sbin/setuser $USER "$@"