[New-bugs-announce] [issue16139] Python 3.3 fails when starting from read-only FS

[Andrew Gallagher]

New submission from Andrew Gallagher:

This occurs when python is installed on a read-only mount AND all the .pyc files are out-of-date.  Therefore, when python starts and attempts to write a new .pyc file, _write_atomic in "Lib/importlib/_bootstrap.py" throws an OSError with an errno of EROFS, which is not handled (and ignored) and kills the interpreter.

$ python
Fatal Python error: Py_Initialize: Unable to get the locale encoding
Traceback (most recent call last):
  File "<frozen importlib._bootstrap>", line 1558, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1525, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 586, in _check_name_wrapper
  File "<frozen importlib._bootstrap>", line 1023, in load_module
  File "<frozen importlib._bootstrap>", line 1004, in load_module
  File "<frozen importlib._bootstrap>", line 562, in module_for_loader_wrapper
  File "<frozen importlib._bootstrap>", line 854, in _load_module
  File "<frozen importlib._bootstrap>", line 990, in get_code
  File "<frozen importlib._bootstrap>", line 1051, in _cache_bytecode
  File "<frozen importlib._bootstrap>", line 1074, in set_data
  File "<frozen importlib._bootstrap>", line 128, in _write_atomic
OSError: [Errno 30] Read-only file system: '<read-only-mount-path>/lib/python3.3/encodings/__pycache__/__init__.cpython-33.pyc.139872939267056'
Aborted (core dumped)

The following (hacky) patch fixes the issue for me:

--- a/Python-3.3.0/Lib/importlib/_bootstrap.py
+++ b/Python-3.3.0/Lib/importlib/_bootstrap.py
@@ -1070,6 +1070,10 @@ class SourceFileLoader(FileLoader, SourceLoader):
                 # If can't get proper access, then just forget about writing
                 # the data.
                 return
+            except OSError as e:
+                if e.errno != 30:  # ignore EROFS
+                    raise
+                return
         try:
             _write_atomic(path, data, _mode)
             _verbose_message('created {!r}', path)
@@ -1077,6 +1081,9 @@ class SourceFileLoader(FileLoader, SourceLoader):
             # Don't worry if you can't write bytecode or someone is writing
             # it at the same time.
             pass
+        except OSError as e:
+            if e.errno != 30:  # ignore EROFS
+                raise

----------
components: Library (Lib)
messages: 172029
nosy: andrewjcg
priority: normal
severity: normal
status: open
title: Python 3.3 fails when starting from read-only FS
type: behavior
versions: Python 3.3

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue16139>
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