Backport PR #10644: system-wide startup files and env config

- adds `{sys.prefix}/etc/ipython` to config-file path, which is commonly used for Jupyter applications in envs
- support startup files in system-wide config directories (e.g. `/etc/ipython/startup`, now `{sys.prefix}/etc/ipython/startup`)

docs/source/whatsnew/pr/env-config.rst

@@ -0,0 +1,5 b''
+
+- IPython now looks for config files in ``{sys.prefix}/etc/ipython``
+  for environment-specific configuration.
+- Startup files can be found in ``/etc/ipython/startup`` or ``{sys.prefix}/etc/ipython/startup``
+  in addition to the profile directory, for system-wide or env-specific startup files.

IPython/core/application.py

@@ -44,6 +44,14 b' else:'
         "/etc/ipython",
     ]
 
+
+ENV_CONFIG_DIRS = []
+_env_config_dir = os.path.join(sys.prefix, 'etc', 'ipython')
+if _env_config_dir not in SYSTEM_CONFIG_DIRS:
+    # only add ENV_CONFIG if sys.prefix is not already included
+    ENV_CONFIG_DIRS.append(_env_config_dir)
+
+
 _envvar = os.environ.get('IPYTHON_SUPPRESS_CONFIG_ERRORS')
 if _envvar in {None, ''}:
     IPYTHON_SUPPRESS_CONFIG_ERRORS = None
@@ -403,6 +411,7 b' class BaseIPythonApplication(Application):'
 
     def init_config_files(self):
         """[optionally] copy default config files into profile dir."""
+        self.config_file_paths.extend(ENV_CONFIG_DIRS)
         self.config_file_paths.extend(SYSTEM_CONFIG_DIRS)
         # copy config files
         path = self.builtin_profile_dir

IPython/core/shellapp.py

@@ -11,12 +11,14 b' from __future__ import absolute_import'
 from __future__ import print_function
 
 import glob
+from itertools import chain
 import os
 import sys
 
 from traitlets.config.application import boolean_flag
 from traitlets.config.configurable import Configurable
 from traitlets.config.loader import Config
+from IPython.core.application import SYSTEM_CONFIG_DIRS, ENV_CONFIG_DIRS
 from IPython.core import pylabtools
 from IPython.utils import py3compat
 from IPython.utils.contexts import preserve_keys
@@ -331,7 +333,9 b' class InteractiveShellApp(Configurable):'
 
     def _run_startup_files(self):
         """Run files from profile startup directory"""
-        startup_dir = self.profile_dir.startup_dir
+        startup_dirs = [self.profile_dir.startup_dir] + [
+            os.path.join(p, 'startup') for p in chain(ENV_CONFIG_DIRS, SYSTEM_CONFIG_DIRS)
+        ]
         startup_files = []
 
         if self.exec_PYTHONSTARTUP and os.environ.get('PYTHONSTARTUP', False) and \
@@ -343,9 +347,9 b' class InteractiveShellApp(Configurable):'
             except:
                 self.log.warning("Unknown error in handling PYTHONSTARTUP file %s:", python_startup)
                 self.shell.showtraceback()
-
-        startup_files += glob.glob(os.path.join(startup_dir, '*.py'))
-        startup_files += glob.glob(os.path.join(startup_dir, '*.ipy'))
+        for startup_dir in startup_dirs[::-1]:
+            startup_files += glob.glob(os.path.join(startup_dir, '*.py'))
+            startup_files += glob.glob(os.path.join(startup_dir, '*.ipy'))
         if not startup_files:
             return