Add a warning when run as root (e.g., sudo pip) (#9394)

news/6409.bugfix.rst

@@ -0,0 +1 @@
+Add a warning, discouraging the usage of pip as root, outside a virtual environment.

src/pip/_internal/cli/base_command.py

@@ -149,8 +149,8 @@ def _main(self, args):
                     "The directory '%s' or its parent directory is not owned "
                     "or is not writable by the current user. The cache "
                     "has been disabled. Check the permissions and owner of "
-                    "that directory. If executing pip with sudo, you may want "
-                    "sudo's -H flag.",
+                    "that directory. If executing pip with sudo, you should "
+                    "use sudo's -H flag.",
                     options.cache_dir,
                 )
                 options.cache_dir = None

src/pip/_internal/cli/req_command.py

@@ -7,6 +7,7 @@
 
 import logging
 import os
+import sys
 from functools import partial
 from optparse import Values
 from typing import Any, List, Optional, Tuple
@@ -38,6 +39,7 @@
     TempDirectoryTypeRegistry,
     tempdir_kinds,
 )
+from pip._internal.utils.virtualenv import running_under_virtualenv
 
 logger = logging.getLogger(__name__)
 
@@ -152,6 +154,35 @@ def handle_pip_version_check(self, options):
 ]
 
 
+def warn_if_run_as_root():
+    # type: () -> None
+    """Output a warning for sudo users on Unix.
+
+    In a virtual environment, sudo pip still writes to virtualenv.
+    On Windows, users may run pip as Administrator without issues.
+    This warning only applies to Unix root users outside of virtualenv.
+    """
+    if running_under_virtualenv():
+        return
+    if not hasattr(os, "getuid"):
+        return
+    # On Windows, there are no "system managed" Python packages. Installing as
+    # Administrator via pip is the correct way of updating system environments.
+    #
+    # We choose sys.platform over utils.compat.WINDOWS here to enable Mypy platform
+    # checks: https://mypy.readthedocs.io/en/stable/common_issues.html
+    if sys.platform == "win32" or sys.platform == "cygwin":
+        return
+    if sys.platform == "darwin" or sys.platform == "linux":
+        if os.getuid() != 0:
+            return
+    logger.warning(
+        "Running pip as root will break packages and permissions. "
+        "You should install packages reliably by using venv: "
+        "https://pip.pypa.io/warnings/venv"
+    )
+
+
 def with_cleanup(func):
     # type: (Any) -> Any
     """Decorator for common logic related to managing temporary

src/pip/_internal/commands/install.py

@@ -12,7 +12,11 @@
 from pip._internal.cache import WheelCache
 from pip._internal.cli import cmdoptions
 from pip._internal.cli.cmdoptions import make_target_python
-from pip._internal.cli.req_command import RequirementCommand, with_cleanup
+from pip._internal.cli.req_command import (
+    RequirementCommand,
+    warn_if_run_as_root,
+    with_cleanup,
+)
 from pip._internal.cli.status_codes import ERROR, SUCCESS
 from pip._internal.exceptions import CommandError, InstallationError
 from pip._internal.locations import get_scheme
@@ -443,6 +447,7 @@ def run(self, options, args):
                 options.target_dir, target_temp_dir, options.upgrade
             )
 
+        warn_if_run_as_root()
         return SUCCESS
 
     def _handle_target_dir(self, target_dir, target_temp_dir, upgrade):

src/pip/_internal/commands/uninstall.py

@@ -4,7 +4,7 @@
 from pip._vendor.packaging.utils import canonicalize_name
 
 from pip._internal.cli.base_command import Command
-from pip._internal.cli.req_command import SessionCommandMixin
+from pip._internal.cli.req_command import SessionCommandMixin, warn_if_run_as_root
 from pip._internal.cli.status_codes import SUCCESS
 from pip._internal.exceptions import InstallationError
 from pip._internal.req import parse_requirements
@@ -88,4 +88,5 @@ def run(self, options, args):
             if uninstall_pathset:
                 uninstall_pathset.commit()
 
+        warn_if_run_as_root()
         return SUCCESS