diff -ru pip-18.0/src/pip/_internal/commands/install.py pip-18.0_patched/src/pip/_internal/commands/install.py
--- pip-18.0/src/pip/_internal/commands/install.py	2018-07-20 06:10:48.000000000 +0200
+++ pip-18.0_patched/src/pip/_internal/commands/install.py	2018-07-31 12:15:43.777317780 +0200
@@ -5,6 +5,8 @@
 import operator
 import os
 import shutil
+import sys
+from os import path
 from optparse import SUPPRESS_HELP
 
 from pip._vendor import pkg_resources
@@ -205,6 +207,18 @@
     def run(self, options, args):
         cmdoptions.check_install_build_global(options)
 
+        def is_venv():
+            return hasattr(sys, 'real_prefix') or \
+                    (hasattr(sys, 'base_prefix') and sys.base_prefix != sys.prefix)
+
+        # Check whether we have root privileges and aren't in venv/virtualenv
+        if os.getuid() == 0 and not is_venv():
+            logger.warning(
+                "WARNING: Running pip install with root privileges is "
+                "generally not a good idea. Try `%s install --user` instead."
+                        % path.basename(sys.argv[0])
+            )
+
         upgrade_strategy = "to-satisfy-only"
         if options.upgrade:
             upgrade_strategy = options.upgrade_strategy
