added option to specify different path to /proc file system (useful in containers); documentation updates

Author: cnelson

README.rst

@@ -5,7 +5,7 @@ NSEnter
 This Python package allows entering Linux kernel namespaces (mount, IPC, net, PID, user and UTS) by doing the "setns" syscall.
 The command line interface tries to be similar to the nsenter_ C program.
 
-Requires Python 3.4.
+Requires Python 2.6 or higher
 
 See the introductory `blog post "Entering Kernel Namespaces from Python"`_.
 

nsenter/__init__.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python
 
 """
 nsenter - run program with namespaces of other processes
@@ -15,7 +15,7 @@
 except ImportError:
     from contextlib2 import ExitStack
 
-NAMESPACE_NAMES = frozenset(['mnt','ipc','net','pid','user','uts'])
+NAMESPACE_NAMES = frozenset(['mnt', 'ipc', 'net', 'pid', 'user', 'uts'])
 
 
 class Namespace(object):
@@ -25,6 +25,9 @@ class Namespace(object):
         pid: The PID for the owner of the namespace to enter
         ns_type: The type of namespace to enter must be one of
             mnt ipc net pid user uts
+        proc: The path to the /proc file system.  If running in a container
+            the host proc file system may be binded mounted in a different
+            location
 
     Raises:
         IOError: A non existent PID was provided
@@ -40,35 +43,36 @@ class Namespace(object):
     _log = logging.getLogger(__name__)
     _libc = ctypes.CDLL('libc.so.6', use_errno=True)
 
-    def __init__(self, pid, ns_type):
+    def __init__(self, pid, ns_type, proc='/proc'):
         if ns_type not in NAMESPACE_NAMES:
             raise ValueError('ns_type must be one of {0}'.format(
                 ', '.join(NAMESPACE_NAMES)
             ))
 
         self.pid = pid
         self.ns_type = ns_type
+        self.proc = proc
 
         self.target_fd = self._nsfd(pid, ns_type).open()
         self.target_fileno = self.target_fd.fileno()
 
         self.parent_fd = self._nsfd('self', ns_type).open()
         self.parent_fileno = self.parent_fd.fileno()
 
-    __init__.__annotations__  = {'pid': str, 'ns_type': str}
+    __init__.__annotations__ = {'pid': str, 'ns_type': str}
 
     def _nsfd(self, pid, ns_type):
-        """Utility method to build a pathlib.Path instance pointing at the 
+        """Utility method to build a pathlib.Path instance pointing at the
         requested namespace entry
 
         Args:
-            pid: The PID 
+            pid: The PID
             ns_type: The namespace type to enter
 
         Returns:
              pathlib.Path pointing to the /proc namespace entry
         """
-        return Path('/proc') / str(pid) / 'ns' / ns_type
+        return Path(self.proc) / str(pid) / 'ns' / ns_type
 
     _nsfd.__annotations__ = {'process': str, 'ns_type': str, 'return': Path}
 
@@ -78,50 +82,55 @@ def _close_files(self):
             self.target_fd.close()
         except:
             pass
-        self.parent_fd.close()    
+        self.parent_fd.close()
 
     def __enter__(self):
         self._log.debug('Entering %s namespace %s', self.ns_type, self.pid)
 
         if self._libc.setns(self.target_fileno, 0) == -1:
             e = ctypes.get_errno()
             self._close_files()
-            raise OSError(e, errno.errorcode[e]) 
+            raise OSError(e, errno.errorcode[e])
 
     def __exit__(self, type, value, tb):
         self._log.debug('Leaving %s namespace %s', self.ns_type, self.pid)
-        
+
         if self._libc.setns(self.parent_fileno, 0) == -1:
             e = ctypes.get_errno()
             self._close_files()
-            raise OSError(e, errno.errorcode[e]) 
+            raise OSError(e, errno.errorcode[e])
 
         self._close_files()
-        
-def main(): #pragma: no cover
-    """Command line interface to the Namespace Contet Manager"""
+
+
+def main():  # pragma: no cover
+    """Command line interface to the Namespace context manager"""
 
     parser = argparse.ArgumentParser(prog='nsenter', description=__doc__)
-    
+
     parser.add_argument('--target', '-t', required=True, metavar='PID',
                         help='A target process to get contexts from')
 
     group = parser.add_argument_group('Namespaces')
 
     for ns in NAMESPACE_NAMES:
-       group.add_argument('--{0}'.format(ns), action='store_true', 
-                            help='Enter the {0} namespace'.format(ns))
-    
-    parser.add_argument('--all', action='store_true', 
-                        help='Enter all namespaces')
+        group.add_argument('--{0}'.format(ns),
+                           action='store_true',
+                           help='Enter the {0} namespace'.format(ns)
+                           )
+
+    parser.add_argument('--all',
+                        action='store_true',
+                        help='Enter all namespaces'
+                        )
 
     parser.add_argument('command', nargs='*', default=['/bin/sh'])
 
     args = parser.parse_args()
 
-    #make sure we have --all or at least one namespace
+    # make sure we have --all or at least one namespace
     if (True not in [getattr(args, ns) for ns in NAMESPACE_NAMES]
-        and not args.all):
+            and not args.all):
         parser.error('You must specify at least one namespace')
 
     try:
@@ -130,9 +139,9 @@ def main(): #pragma: no cover
             for ns in NAMESPACE_NAMES:
                 if getattr(args, ns) or args.all:
                     namespaces.append(Namespace(args.target, ns))
-           
+
             for ns in namespaces:
-                 stack.enter_context(ns)
+                stack.enter_context(ns)
 
             os.execlp(args.command[0], *args.command)
     except IOError as exc:
@@ -143,5 +152,5 @@ def main(): #pragma: no cover
         ))
 
 
-if __name__ == '__main__': #pragma: no cover
+if __name__ == '__main__':  # pragma: no cover
     main()

tests.py

@@ -19,8 +19,6 @@ def tearDown(self):
 
     def test_namespaces_except_user(self):
         """Test entering all namespaces execept user
-
-        Must have CAP_SYS_ADMIN to run these tests properly
         """
 
         #Can't use the assertRaises context manager in python2.6