netbox-community#1090: Tweaked docs for Python3 on Ubuntu

docs/installation/netbox.md

@@ -8,6 +8,13 @@ Python 3:
 # apt-get install -y python3 python3-dev python3-pip libxml2-dev libxslt1-dev libffi-dev graphviz libpq-dev libssl-dev
 ```
 
+!!! warning
+    On Ubuntu, installing only Python3 will not create a symlink for the interpreter at `/usr/bin/python`: scripts need to be called using the `python3` binary explicitly. As a workaround, you can create this symlink using the `update-alternatives` utility:
+
+        # update-alternatives --install /usr/bin/python python /usr/bin/python3 1
+
+    This will allow calling the `python3` binary as `python`.
+
 Python 2:
 
 ```no-highlight
@@ -84,6 +91,14 @@ Checking connectivity... done.
 
 Install the required Python packages using pip. (If you encounter any compilation errors during this step, ensure that you've installed all of the system dependencies listed above.)
 
+Python 3:
+
+```no-highlight
+# pip3 install -r requirements.txt
+```
+
+Python 2:
+
 ```no-highlight
 # pip install -r requirements.txt
 ```

docs/installation/postgresql.md

@@ -5,13 +5,14 @@ NetBox requires a PostgreSQL database to store data. (Please note that MySQL is
 **Debian/Ubuntu**
 
 ```no-highlight
-# apt-get install -y postgresql libpq-dev python-psycopg2
+# apt-get update
+# apt-get install -y postgresql libpq-dev
 ```
 
 **CentOS/RHEL**
 
 ```no-highlight
-# yum install -y postgresql postgresql-server postgresql-devel python-psycopg2
+# yum install -y postgresql postgresql-server postgresql-devel
 # postgresql-setup initdb
 ```
 

upgrade.sh

@@ -15,8 +15,12 @@ if [ "$(whoami)" = "root" ]; then
 	PREFIX=""
 fi
 
+# Fall back to pip3 if pip is missing
+PIP="pip"
+type $PIP >/dev/null 2>&1 || PIP="pip3"
+
 # Install any new Python packages
-COMMAND="${PREFIX}pip install -r requirements.txt --upgrade"
+COMMAND="${PREFIX}${PIP} install -r requirements.txt --upgrade"
 echo "Updating required Python packages ($COMMAND)..."
 eval $COMMAND