diff --git a/Tools/setup/ubuntu.sh b/Tools/setup/ubuntu.sh
index d327b53e3b..145bf773c3 100755
--- a/Tools/setup/ubuntu.sh
+++ b/Tools/setup/ubuntu.sh
@@ -1,5 +1,17 @@
 #! /usr/bin/env bash
 
+## Bash script to setup PX4 development environment on Ubuntu LTS (18.04, 16.04).
+## Can also be used in docker.
+##
+## Installs:
+## - Common dependencies and tools for nuttx, jMAVSim, Gazebo
+## - NuttX toolchain (omit with arg: --no-nuttx)
+## - jMAVSim and Gazebo9 simulator (omit with arg: --no-sim-tools)
+##
+## Not Installs:
+## - FastRTPS and FastCDR
+
+
 INSTALL_NUTTX="true"
 INSTALL_SIM="true"
 
@@ -33,6 +45,14 @@ fi
 # script directory
 DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
 
+# check requirements.txt exists (script not run in source tree)
+REQUIREMENTS_FILE="requirements.txt"
+if [[ ! -f "${DIR}/${REQUIREMENTS_FILE}" ]]; then
+	echo "FAILED: ${REQUIREMENTS_FILE} needed in same directory as ubuntu.sh (${DIR})."
+        return 1
+fi
+
+
 # check ubuntu version
 # instructions for 16.04, 18.04
 # otherwise warn and point to docker?
@@ -47,6 +67,8 @@ elif [[ "${UBUNTU_RELEASE}" == "18.04" ]]; then
 	echo "Ubuntu 18.04"
 fi
 
+
+
 export DEBIAN_FRONTEND=noninteractive
 
 echo