cpython/Lib/test/test_posix.py

"Test posix functions"

from test import support
from test.support import is_apple
from test.support import os_helper
from test.support import warnings_helper
from test.support.script_helper import assert_python_ok

import errno
import sys
import signal
import time
import os
import platform
import stat
import tempfile
import unittest
import warnings
import textwrap
from contextlib import contextmanager

try:
    import posix
except ImportError:
    import nt as posix

try:
    import pwd
except ImportError:
    pwd = None

_DUMMY_SYMLINK = os.path.join(tempfile.gettempdir(),
                              os_helper.TESTFN + '-dummy-symlink')

requires_32b = unittest.skipUnless(
    # Emscripten/WASI have 32 bits pointers, but support 64 bits syscall args.
    sys.maxsize < 2**32 and not (support.is_emscripten or support.is_wasi),
    'test is only meaningful on 32-bit builds'
)

def _supports_sched():
    if not hasattr(posix, 'sched_getscheduler'):
        return False
    try:
        posix.sched_getscheduler(0)
    except OSError as e:
        if e.errno == errno.ENOSYS:
            return False
    return True

requires_sched = unittest.skipUnless(_supports_sched(), 'requires POSIX scheduler API')


class PosixTester(unittest.TestCase):

    def setUp(self):
        # create empty file
        self.addCleanup(os_helper.unlink, os_helper.TESTFN)
        with open(os_helper.TESTFN, "wb"):
            pass
        self.enterContext(warnings_helper.check_warnings())
        warnings.filterwarnings('ignore', '.* potential security risk .*',
                                RuntimeWarning)

    def testNoArgFunctions(self):
        # test posix functions which take no arguments and have
        # no side-effects which we need to cleanup (e.g., fork, wait, abort)
        NO_ARG_FUNCTIONS = [ "ctermid", "getcwd", "getcwdb", "uname",
                             "times", "getloadavg",
                             "getegid", "geteuid", "getgid", "getgroups",
                             "getpid", "getpgrp", "getppid", "getuid", "sync",
                           ]

        for name in NO_ARG_FUNCTIONS:
            posix_func = getattr(posix, name, None)
            if posix_func is not None:
                with self.subTest(name):
                    posix_func()
                    self.assertRaises(TypeError, posix_func, 1)

    @unittest.skipUnless(hasattr(posix, 'getresuid'),
                         'test needs posix.getresuid()')
    def test_getresuid(self):
        user_ids = posix.getresuid()
        self.assertEqual(len(user_ids), 3)
        for val in user_ids:
            self.assertGreaterEqual(val, 0)

    @unittest.skipUnless(hasattr(posix, 'getresgid'),
                         'test needs posix.getresgid()')
    def test_getresgid(self):
        group_ids = posix.getresgid()
        self.assertEqual(len(group_ids), 3)
        for val in group_ids:
            self.assertGreaterEqual(val, 0)

    @unittest.skipUnless(hasattr(posix, 'setresuid'),
                         'test needs posix.setresuid()')
    def test_setresuid(self):
        current_user_ids = posix.getresuid()
        self.assertIsNone(posix.setresuid(*current_user_ids))
        # -1 means don't change that value.
        self.assertIsNone(posix.setresuid(-1, -1, -1))

    @unittest.skipUnless(hasattr(posix, 'setresuid'),
                         'test needs posix.setresuid()')
    def test_setresuid_exception(self):
        # Don't do this test if someone is silly enough to run us as root.
        current_user_ids = posix.getresuid()
        if 0 not in current_user_ids:
            new_user_ids = (current_user_ids[0]+1, -1, -1)
            self.assertRaises(OSError, posix.setresuid, *new_user_ids)

    @unittest.skipUnless(hasattr(posix, 'setresgid'),
                         'test needs posix.setresgid()')
    def test_setresgid(self):
        current_group_ids = posix.getresgid()
        self.assertIsNone(posix.setresgid(*current_group_ids))
        # -1 means don't change that value.
        self.assertIsNone(posix.setresgid(-1, -1, -1))

    @unittest.skipUnless(hasattr(posix, 'setresgid'),
                         'test needs posix.setresgid()')
    def test_setresgid_exception(self):
        # Don't do this test if someone is silly enough to run us as root.
        current_group_ids = posix.getresgid()
        if 0 not in current_group_ids:
            new_group_ids = (current_group_ids[0]+1, -1, -1)
            self.assertRaises(OSError, posix.setresgid, *new_group_ids)

    @unittest.skipUnless(hasattr(posix, 'initgroups'),
                         "test needs os.initgroups()")
    @unittest.skipUnless(hasattr(pwd, 'getpwuid'), "test needs pwd.getpwuid()")
    def test_initgroups(self):
        # It takes a string and an integer; check that it raises a TypeError
        # for other argument lists.
        self.assertRaises(TypeError, posix.initgroups)
        self.assertRaises(TypeError, posix.initgroups, None)
        self.assertRaises(TypeError, posix.initgroups, 3, "foo")
        self.assertRaises(TypeError, posix.initgroups, "foo", 3, object())

        # If a non-privileged user invokes it, it should fail with OSError
        # EPERM.
        if os.getuid() != 0:
            try:
                name = pwd.getpwuid(posix.getuid()).pw_name
            except KeyError:
                # the current UID may not have a pwd entry
                raise unittest.SkipTest("need a pwd entry")
            try:
                posix.initgroups(name, 13)
            except OSError as e:
                self.assertEqual(e.errno, errno.EPERM)
            else:
                self.fail("Expected OSError to be raised by initgroups")

    @unittest.skipUnless(hasattr(posix, 'statvfs'),
                         'test needs posix.statvfs()')
    def test_statvfs(self):
        self.assertTrue(posix.statvfs(os.curdir))

    @unittest.skipUnless(hasattr(posix, 'fstatvfs'),
                         'test needs posix.fstatvfs()')
    def test_fstatvfs(self):
        fp = open(os_helper.TESTFN)
        try:
            self.assertTrue(posix.fstatvfs(fp.fileno()))
            self.assertTrue(posix.statvfs(fp.fileno()))
        finally:
            fp.close()

    @unittest.skipUnless(hasattr(posix, 'ftruncate'),
                         'test needs posix.ftruncate()')
    def test_ftruncate(self):
        fp = open(os_helper.TESTFN, 'w+')
        try:
            # we need to have some data to truncate
            fp.write('test')
            fp.flush()
            posix.ftruncate(fp.fileno(), 0)
        finally:
            fp.close()

    @unittest.skipUnless(hasattr(posix, 'truncate'), "test needs posix.truncate()")
    def test_truncate(self):
        with open(os_helper.TESTFN, 'w') as fp:
            fp.write('test')
            fp.flush()
        posix.truncate(os_helper.TESTFN, 0)

    @unittest.skipUnless(getattr(os, 'execve', None) in os.supports_fd, "test needs execve() to support the fd parameter")
    @support.requires_fork()
    def test_fexecve(self):
        fp = os.open(sys.executable, os.O_RDONLY)
        try:
            pid = os.fork()
            if pid == 0:
                os.chdir(os.path.split(sys.executable)[0])
                posix.execve(fp, [sys.executable, '-c', 'pass'], os.environ)
            else:
                support.wait_process(pid, exitcode=0)
        finally:
            os.close(fp)


    @unittest.skipUnless(hasattr(posix, 'waitid'), "test needs posix.waitid()")
    @support.requires_fork()
    def test_waitid(self):
        pid = os.fork()
        if pid == 0:
            os.chdir(os.path.split(sys.executable)[0])
            posix.execve(sys.executable, [sys.executable, '-c', 'pass'], os.environ)
        else:
            res = posix.waitid(posix.P_PID, pid, posix.WEXITED)
            self.assertEqual(pid, res.si_pid)

    @support.requires_fork()
    def test_register_at_fork(self):
        with self.assertRaises(TypeError, msg="Positional args not allowed"):
            os.register_at_fork(lambda: None)
        with self.assertRaises(TypeError, msg="Args must be callable"):
            os.register_at_fork(before=2)
        with self.assertRaises(TypeError, msg="Args must be callable"):
            os.register_at_fork(after_in_child="three")
        with self.assertRaises(TypeError, msg="Args must be callable"):
            os.register_at_fork(after_in_parent=b"Five")
        with self.assertRaises(TypeError, msg="Args must not be None"):
            os.register_at_fork(before=None)
        with self.assertRaises(TypeError, msg="Args must not be None"):
            os.register_at_fork(after_in_child=None)
        with self.assertRaises(TypeError, msg="Args must not be None"):
            os.register_at_fork(after_in_parent=None)
        with self.assertRaises(TypeError, msg="Invalid arg was allowed"):
            # Ensure a combination of valid and invalid is an error.
            os.register_at_fork(before=None, after_in_parent=lambda: 3)
        with self.assertRaises(TypeError, msg="At least one argument is required"):
            # when no arg is passed
            os.register_at_fork()
        with self.assertRaises(TypeError, msg="Invalid arg was allowed"):
            # Ensure a combination of valid and invalid is an error.
            os.register_at_fork(before=lambda: None, after_in_child='')
        # We test actual registrations in their own process so as not to
        # pollute this one.  There is no way to unregister for cleanup.
        code = """if 1:
            import os

            r, w = os.pipe()
            fin_r, fin_w = os.pipe()

            os.register_at_fork(before=lambda: os.write(w, b'A'))
            os.register_at_fork(after_in_parent=lambda: os.write(w, b'C'))
            os.register_at_fork(after_in_child=lambda: os.write(w, b'E'))
            os.register_at_fork(before=lambda: os.write(w, b'B'),
                                after_in_parent=lambda: os.write(w, b'D'),
                                after_in_child=lambda: os.write(w, b'F'))

            pid = os.fork()
            if pid == 0:
                # At this point, after-forkers have already been executed
                os.close(w)
                # Wait for parent to tell us to exit
                os.read(fin_r, 1)
                os._exit(0)
            else:
                try:
                    os.close(w)
                    with open(r, "rb") as f:
                        data = f.read()
                        assert len(data) == 6, data
                        # Check before-fork callbacks
                        assert data[:2] == b'BA', data
                        # Check after-fork callbacks
                        assert sorted(data[2:]) == list(b'CDEF'), data
                        assert data.index(b'C') < data.index(b'D'), data
                        assert data.index(b'E') < data.index(b'F'), data
                finally:
                    os.write(fin_w, b'!')
            """
        assert_python_ok('-c', code)

    @unittest.skipUnless(hasattr(posix, 'lockf'), "test needs posix.lockf()")
    def test_lockf(self):
        fd = os.open(os_helper.TESTFN, os.O_WRONLY | os.O_CREAT)
        try:
            os.write(fd, b'test')
            os.lseek(fd, 0, os.SEEK_SET)
            posix.lockf(fd, posix.F_LOCK, 4)
            # section is locked
            posix.lockf(fd, posix.F_ULOCK, 4)
        finally:
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'pread'), "test needs posix.pread()")
    def test_pread(self):
        fd = os.open(os_helper.TESTFN, os.O_RDWR | os.O_CREAT)
        try:
            os.write(fd, b'test')
            os.lseek(fd, 0, os.SEEK_SET)
            self.assertEqual(b'es', posix.pread(fd, 2, 1))
            # the first pread() shouldn't disturb the file offset
            self.assertEqual(b'te', posix.read(fd, 2))
        finally:
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'preadv'), "test needs posix.preadv()")
    def test_preadv(self):
        fd = os.open(os_helper.TESTFN, os.O_RDWR | os.O_CREAT)
        try:
            os.write(fd, b'test1tt2t3t5t6t6t8')
            buf = [bytearray(i) for i in [5, 3, 2]]
            self.assertEqual(posix.preadv(fd, buf, 3), 10)
            self.assertEqual([b't1tt2', b't3t', b'5t'], list(buf))
        finally:
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'preadv'), "test needs posix.preadv()")
    @unittest.skipUnless(hasattr(posix, 'RWF_HIPRI'), "test needs posix.RWF_HIPRI")
    def test_preadv_flags(self):
        fd = os.open(os_helper.TESTFN, os.O_RDWR | os.O_CREAT)
        try:
            os.write(fd, b'test1tt2t3t5t6t6t8')
            buf = [bytearray(i) for i in [5, 3, 2]]
            self.assertEqual(posix.preadv(fd, buf, 3, os.RWF_HIPRI), 10)
            self.assertEqual([b't1tt2', b't3t', b'5t'], list(buf))
        except NotImplementedError:
            self.skipTest("preadv2 not available")
        except OSError as inst:
            # Is possible that the macro RWF_HIPRI was defined at compilation time
            # but the option is not supported by the kernel or the runtime libc shared
            # library.
            if inst.errno in {errno.EINVAL, errno.ENOTSUP}:
                raise unittest.SkipTest("RWF_HIPRI is not supported by the current system")
            else:
                raise
        finally:
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'preadv'), "test needs posix.preadv()")
    @requires_32b
    def test_preadv_overflow_32bits(self):
        fd = os.open(os_helper.TESTFN, os.O_RDWR | os.O_CREAT)
        try:
            buf = [bytearray(2**16)] * 2**15
            with self.assertRaises(OSError) as cm:
                os.preadv(fd, buf, 0)
            self.assertEqual(cm.exception.errno, errno.EINVAL)
            self.assertEqual(bytes(buf[0]), b'\0'* 2**16)
        finally:
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'pwrite'), "test needs posix.pwrite()")
    def test_pwrite(self):
        fd = os.open(os_helper.TESTFN, os.O_RDWR | os.O_CREAT)
        try:
            os.write(fd, b'test')
            os.lseek(fd, 0, os.SEEK_SET)
            posix.pwrite(fd, b'xx', 1)
            self.assertEqual(b'txxt', posix.read(fd, 4))
        finally:
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'pwritev'), "test needs posix.pwritev()")
    def test_pwritev(self):
        fd = os.open(os_helper.TESTFN, os.O_RDWR | os.O_CREAT)
        try:
            os.write(fd, b"xx")
            os.lseek(fd, 0, os.SEEK_SET)
            n = os.pwritev(fd, [b'test1', b'tt2', b't3'], 2)
            self.assertEqual(n, 10)

            os.lseek(fd, 0, os.SEEK_SET)
            self.assertEqual(b'xxtest1tt2t3', posix.read(fd, 100))
        finally:
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'pwritev'), "test needs posix.pwritev()")
    @unittest.skipUnless(hasattr(posix, 'os.RWF_SYNC'), "test needs os.RWF_SYNC")
    def test_pwritev_flags(self):
        fd = os.open(os_helper.TESTFN, os.O_RDWR | os.O_CREAT)
        try:
            os.write(fd,b"xx")
            os.lseek(fd, 0, os.SEEK_SET)
            n = os.pwritev(fd, [b'test1', b'tt2', b't3'], 2, os.RWF_SYNC)
            self.assertEqual(n, 10)

            os.lseek(fd, 0, os.SEEK_SET)
            self.assertEqual(b'xxtest1tt2', posix.read(fd, 100))
        finally:
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'pwritev'), "test needs posix.pwritev()")
    @requires_32b
    def test_pwritev_overflow_32bits(self):
        fd = os.open(os_helper.TESTFN, os.O_RDWR | os.O_CREAT)
        try:
            with self.assertRaises(OSError) as cm:
                os.pwritev(fd, [b"x" * 2**16] * 2**15, 0)
            self.assertEqual(cm.exception.errno, errno.EINVAL)
        finally:
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'posix_fallocate'),
        "test needs posix.posix_fallocate()")
    def test_posix_fallocate(self):
        fd = os.open(os_helper.TESTFN, os.O_WRONLY | os.O_CREAT)
        try:
            posix.posix_fallocate(fd, 0, 10)
        except OSError as inst:
            # issue10812, ZFS doesn't appear to support posix_fallocate,
            # so skip Solaris-based since they are likely to have ZFS.
            # issue33655: Also ignore EINVAL on *BSD since ZFS is also
            # often used there.
            if inst.errno == errno.EINVAL and sys.platform.startswith(
                ('sunos', 'freebsd', 'openbsd', 'gnukfreebsd')):
                raise unittest.SkipTest("test may fail on ZFS filesystems")
            elif inst.errno == errno.EOPNOTSUPP and sys.platform.startswith("netbsd"):
                raise unittest.SkipTest("test may fail on FFS filesystems")
            else:
                raise
        finally:
            os.close(fd)

    # issue31106 - posix_fallocate() does not set error in errno.
    @unittest.skipUnless(hasattr(posix, 'posix_fallocate'),
        "test needs posix.posix_fallocate()")
    def test_posix_fallocate_errno(self):
        try:
            posix.posix_fallocate(-42, 0, 10)
        except OSError as inst:
            if inst.errno != errno.EBADF:
                raise

    @unittest.skipUnless(hasattr(posix, 'posix_fadvise'),
        "test needs posix.posix_fadvise()")
    def test_posix_fadvise(self):
        fd = os.open(os_helper.TESTFN, os.O_RDONLY)
        try:
            posix.posix_fadvise(fd, 0, 0, posix.POSIX_FADV_WILLNEED)
        finally:
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'posix_fadvise'),
        "test needs posix.posix_fadvise()")
    def test_posix_fadvise_errno(self):
        try:
            posix.posix_fadvise(-42, 0, 0, posix.POSIX_FADV_WILLNEED)
        except OSError as inst:
            if inst.errno != errno.EBADF:
                raise

    @unittest.skipUnless(os.utime in os.supports_fd, "test needs fd support in os.utime")
    def test_utime_with_fd(self):
        now = time.time()
        fd = os.open(os_helper.TESTFN, os.O_RDONLY)
        try:
            posix.utime(fd)
            posix.utime(fd, None)
            self.assertRaises(TypeError, posix.utime, fd, (None, None))
            self.assertRaises(TypeError, posix.utime, fd, (now, None))
            self.assertRaises(TypeError, posix.utime, fd, (None, now))
            posix.utime(fd, (int(now), int(now)))
            posix.utime(fd, (now, now))
            self.assertRaises(ValueError, posix.utime, fd, (now, now), ns=(now, now))
            self.assertRaises(ValueError, posix.utime, fd, (now, 0), ns=(None, None))
            self.assertRaises(ValueError, posix.utime, fd, (None, None), ns=(now, 0))
            posix.utime(fd, (int(now), int((now - int(now)) * 1e9)))
            posix.utime(fd, ns=(int(now), int((now - int(now)) * 1e9)))

        finally:
            os.close(fd)

    @unittest.skipUnless(os.utime in os.supports_follow_symlinks, "test needs follow_symlinks support in os.utime")
    def test_utime_nofollow_symlinks(self):
        now = time.time()
        posix.utime(os_helper.TESTFN, None, follow_symlinks=False)
        self.assertRaises(TypeError, posix.utime, os_helper.TESTFN,
                          (None, None), follow_symlinks=False)
        self.assertRaises(TypeError, posix.utime, os_helper.TESTFN,
                          (now, None), follow_symlinks=False)
        self.assertRaises(TypeError, posix.utime, os_helper.TESTFN,
                          (None, now), follow_symlinks=False)
        posix.utime(os_helper.TESTFN, (int(now), int(now)),
                    follow_symlinks=False)
        posix.utime(os_helper.TESTFN, (now, now), follow_symlinks=False)
        posix.utime(os_helper.TESTFN, follow_symlinks=False)

    @unittest.skipUnless(hasattr(posix, 'writev'), "test needs posix.writev()")
    def test_writev(self):
        fd = os.open(os_helper.TESTFN, os.O_RDWR | os.O_CREAT)
        try:
            n = os.writev(fd, (b'test1', b'tt2', b't3'))
            self.assertEqual(n, 10)

            os.lseek(fd, 0, os.SEEK_SET)
            self.assertEqual(b'test1tt2t3', posix.read(fd, 10))

            # Issue #20113: empty list of buffers should not crash
            try:
                size = posix.writev(fd, [])
            except OSError:
                # writev(fd, []) raises OSError(22, "Invalid argument")
                # on OpenIndiana
                pass
            else:
                self.assertEqual(size, 0)
        finally:
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'writev'), "test needs posix.writev()")
    @requires_32b
    def test_writev_overflow_32bits(self):
        fd = os.open(os_helper.TESTFN, os.O_RDWR | os.O_CREAT)
        try:
            with self.assertRaises(OSError) as cm:
                os.writev(fd, [b"x" * 2**16] * 2**15)
            self.assertEqual(cm.exception.errno, errno.EINVAL)
        finally:
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'readv'), "test needs posix.readv()")
    def test_readv(self):
        fd = os.open(os_helper.TESTFN, os.O_RDWR | os.O_CREAT)
        try:
            os.write(fd, b'test1tt2t3')
            os.lseek(fd, 0, os.SEEK_SET)
            buf = [bytearray(i) for i in [5, 3, 2]]
            self.assertEqual(posix.readv(fd, buf), 10)
            self.assertEqual([b'test1', b'tt2', b't3'], [bytes(i) for i in buf])

            # Issue #20113: empty list of buffers should not crash
            try:
                size = posix.readv(fd, [])
            except OSError:
                # readv(fd, []) raises OSError(22, "Invalid argument")
                # on OpenIndiana
                pass
            else:
                self.assertEqual(size, 0)
        finally:
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'readv'), "test needs posix.readv()")
    @requires_32b
    def test_readv_overflow_32bits(self):
        fd = os.open(os_helper.TESTFN, os.O_RDWR | os.O_CREAT)
        try:
            buf = [bytearray(2**16)] * 2**15
            with self.assertRaises(OSError) as cm:
                os.readv(fd, buf)
            self.assertEqual(cm.exception.errno, errno.EINVAL)
            self.assertEqual(bytes(buf[0]), b'\0'* 2**16)
        finally:
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'dup'),
                         'test needs posix.dup()')
    @unittest.skipIf(support.is_wasi, "WASI does not have dup()")
    def test_dup(self):
        fp = open(os_helper.TESTFN)
        try:
            fd = posix.dup(fp.fileno())
            self.assertIsInstance(fd, int)
            os.close(fd)
        finally:
            fp.close()

    @unittest.skipUnless(hasattr(posix, 'confstr'),
                         'test needs posix.confstr()')
    @unittest.skipIf(support.is_apple_mobile, "gh-118201: Test is flaky on iOS")
    def test_confstr(self):
        self.assertRaises(ValueError, posix.confstr, "CS_garbage")
        self.assertEqual(len(posix.confstr("CS_PATH")) > 0, True)

    @unittest.skipUnless(hasattr(posix, 'dup2'),
                         'test needs posix.dup2()')
    @unittest.skipIf(support.is_wasi, "WASI does not have dup2()")
    def test_dup2(self):
        fp1 = open(os_helper.TESTFN)
        fp2 = open(os_helper.TESTFN)
        try:
            posix.dup2(fp1.fileno(), fp2.fileno())
        finally:
            fp1.close()
            fp2.close()

    @unittest.skipUnless(hasattr(os, 'O_CLOEXEC'), "needs os.O_CLOEXEC")
    @support.requires_linux_version(2, 6, 23)
    @support.requires_subprocess()
    def test_oscloexec(self):
        fd = os.open(os_helper.TESTFN, os.O_RDONLY|os.O_CLOEXEC)
        self.addCleanup(os.close, fd)
        self.assertFalse(os.get_inheritable(fd))

    @unittest.skipUnless(hasattr(posix, 'O_EXLOCK'),
                         'test needs posix.O_EXLOCK')
    def test_osexlock(self):
        fd = os.open(os_helper.TESTFN,
                     os.O_WRONLY|os.O_EXLOCK|os.O_CREAT)
        self.assertRaises(OSError, os.open, os_helper.TESTFN,
                          os.O_WRONLY|os.O_EXLOCK|os.O_NONBLOCK)
        os.close(fd)

        if hasattr(posix, "O_SHLOCK"):
            fd = os.open(os_helper.TESTFN,
                         os.O_WRONLY|os.O_SHLOCK|os.O_CREAT)
            self.assertRaises(OSError, os.open, os_helper.TESTFN,
                              os.O_WRONLY|os.O_EXLOCK|os.O_NONBLOCK)
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'O_SHLOCK'),
                         'test needs posix.O_SHLOCK')
    def test_osshlock(self):
        fd1 = os.open(os_helper.TESTFN,
                     os.O_WRONLY|os.O_SHLOCK|os.O_CREAT)
        fd2 = os.open(os_helper.TESTFN,
                      os.O_WRONLY|os.O_SHLOCK|os.O_CREAT)
        os.close(fd2)
        os.close(fd1)

        if hasattr(posix, "O_EXLOCK"):
            fd = os.open(os_helper.TESTFN,
                         os.O_WRONLY|os.O_SHLOCK|os.O_CREAT)
            self.assertRaises(OSError, os.open, os_helper.TESTFN,
                              os.O_RDONLY|os.O_EXLOCK|os.O_NONBLOCK)
            os.close(fd)

    @unittest.skipUnless(hasattr(posix, 'fstat'),
                         'test needs posix.fstat()')
    def test_fstat(self):
        fp = open(os_helper.TESTFN)
        try:
            self.assertTrue(posix.fstat(fp.fileno()))
            self.assertTrue(posix.stat(fp.fileno()))

            self.assertRaisesRegex(TypeError,
                    'should be string, bytes, os.PathLike or integer, not',
                    posix.stat, float(fp.fileno()))
        finally:
            fp.close()

    def test_stat(self):
        self.assertTrue(posix.stat(os_helper.TESTFN))
        self.assertTrue(posix.stat(os.fsencode(os_helper.TESTFN)))

        self.assertRaisesRegex(TypeError,
                'should be string, bytes, os.PathLike or integer, not',
                posix.stat, bytearray(os.fsencode(os_helper.TESTFN)))
        self.assertRaisesRegex(TypeError,
                'should be string, bytes, os.PathLike or integer, not',
                posix.stat, None)
        self.assertRaisesRegex(TypeError,
                'should be string, bytes, os.PathLike or integer, not',
                posix.stat, list(os_helper.TESTFN))
        self.assertRaisesRegex(TypeError,
                'should be string, bytes, os.PathLike or integer, not',
                posix.stat, list(os.fsencode(os_helper.TESTFN)))

    @unittest.skipUnless(hasattr(posix, 'mkfifo'), "don't have mkfifo()")
    def test_mkfifo(self):
        if sys.platform == "vxworks":
            fifo_path = os.path.join("/fifos/", os_helper.TESTFN)
        else:
            fifo_path = os_helper.TESTFN
        os_helper.unlink(fifo_path)
        self.addCleanup(os_helper.unlink, fifo_path)
        try:
            posix.mkfifo(fifo_path, stat.S_IRUSR | stat.S_IWUSR)
        except PermissionError as e:
            self.skipTest('posix.mkfifo(): %s' % e)
        self.assertTrue(stat.S_ISFIFO(posix.stat(fifo_path).st_mode))

    @unittest.skipUnless(hasattr(posix, 'mknod') and hasattr(stat, 'S_IFIFO'),
                         "don't have mknod()/S_IFIFO")
    def test_mknod(self):
        # Test using mknod() to create a FIFO (the only use specified
        # by POSIX).
        os_helper.unlink(os_helper.TESTFN)
        mode = stat.S_IFIFO | stat.S_IRUSR | stat.S_IWUSR
        try:
            posix.mknod(os_helper.TESTFN, mode, 0)
        except OSError as e:
            # Some old systems don't allow unprivileged users to use
            # mknod(), or only support creating device nodes.
            self.assertIn(e.errno, (errno.EPERM, errno.EINVAL, errno.EACCES))
        else:
            self.assertTrue(stat.S_ISFIFO(posix.stat(os_helper.TESTFN).st_mode))

        # Keyword arguments are also supported
        os_helper.unlink(os_helper.TESTFN)
        try:
            posix.mknod(path=os_helper.TESTFN, mode=mode, device=0,
                dir_fd=None)
        except OSError as e:
            self.assertIn(e.errno, (errno.EPERM, errno.EINVAL, errno.EACCES))

    @unittest.skipUnless(hasattr(posix, 'makedev'), 'test needs posix.makedev()')
    def test_makedev(self):
        st = posix.stat(os_helper.TESTFN)
        dev = st.st_dev
        self.assertIsInstance(dev, int)
        self.assertGreaterEqual(dev, 0)

        major = posix.major(dev)
        self.assertIsInstance(major, int)
        self.assertGreaterEqual(major, 0)
        self.assertEqual(posix.major(dev), major)
        self.assertRaises(TypeError, posix.major, float(dev))
        self.assertRaises(TypeError, posix.major)
        for x in -2, 2**64, -2**63-1:
            self.assertRaises((ValueError, OverflowError), posix.major, x)

        minor = posix.minor(dev)
        self.assertIsInstance(minor, int)
        self.assertGreaterEqual(minor, 0)
        self.assertEqual(posix.minor(dev), minor)
        self.assertRaises(TypeError, posix.minor, float(dev))
        self.assertRaises(TypeError, posix.minor)
        for x in -2, 2**64, -2**63-1:
            self.assertRaises((ValueError, OverflowError), posix.minor, x)

        self.assertEqual(posix.makedev(major, minor), dev)
        self.assertRaises(TypeError, posix.makedev, float(major), minor)
        self.assertRaises(TypeError, posix.makedev, major, float(minor))
        self.assertRaises(TypeError, posix.makedev, major)
        self.assertRaises(TypeError, posix.makedev)
        for x in -2, 2**32, 2**64, -2**63-1:
            self.assertRaises((ValueError, OverflowError), posix.makedev, x, minor)
            self.assertRaises((ValueError, OverflowError), posix.makedev, major, x)

        if sys.platform == 'linux':
            NODEV = -1
            self.assertEqual(posix.major(NODEV), NODEV)
            self.assertEqual(posix.minor(NODEV), NODEV)
            self.assertEqual(posix.makedev(NODEV, NODEV), NODEV)

    def _test_all_chown_common(self, chown_func, first_param, stat_func):
        """Common code for chown, fchown and lchown tests."""
        def check_stat(uid, gid):
            if stat_func is not None:
                stat = stat_func(first_param)
                self.assertEqual(stat.st_uid, uid)
                self.assertEqual(stat.st_gid, gid)
        uid = os.getuid()
        gid = os.getgid()
        # test a successful chown call
        chown_func(first_param, uid, gid)
        check_stat(uid, gid)
        chown_func(first_param, -1, gid)
        check_stat(uid, gid)
        chown_func(first_param, uid, -1)
        check_stat(uid, gid)

        if sys.platform == "vxworks":
            # On VxWorks, root user id is 1 and 0 means no login user:
            # both are super users.
            is_root = (uid in (0, 1))
        else:
            is_root = (uid == 0)
        if support.is_emscripten:
            # Emscripten getuid() / geteuid() always return 0 (root), but
            # cannot chown uid/gid to random value.
            pass
        elif is_root:
            # Try an amusingly large uid/gid to make sure we handle
            # large unsigned values.  (chown lets you use any
            # uid/gid you like, even if they aren't defined.)
            #
            # On VxWorks uid_t is defined as unsigned short. A big
            # value greater than 65535 will result in underflow error.
            #
            # This problem keeps coming up:
            #   http://bugs.python.org/issue1747858
            #   http://bugs.python.org/issue4591
            #   http://bugs.python.org/issue15301
            # Hopefully the fix in 4591 fixes it for good!
            #
            # This part of the test only runs when run as root.
            # Only scary people run their tests as root.

            big_value = (2**31 if sys.platform != "vxworks" else 2**15)
            chown_func(first_param, big_value, big_value)
            check_stat(big_value, big_value)
            chown_func(first_param, -1, -1)
            check_stat(big_value, big_value)
            chown_func(first_param, uid, gid)
            check_stat(uid, gid)
        elif platform.system() in ('HP-UX', 'SunOS'):
            # HP-UX and Solaris can allow a non-root user to chown() to root
            # (issue #5113)
            raise unittest.SkipTest("Skipping because of non-standard chown() "
                                    "behavior")
        else:
            # non-root cannot chown to root, raises OSError
            self.assertRaises(OSError, chown_func, first_param, 0, 0)
            check_stat(uid, gid)
            self.assertRaises(OSError, chown_func, first_param, 0, -1)
            check_stat(uid, gid)
            if hasattr(os, 'getgroups'):
                if 0 not in os.getgroups():
                    self.assertRaises(OSError, chown_func, first_param, -1, 0)
                    check_stat(uid, gid)
        # test illegal types
        for t in str, float:
            self.assertRaises(TypeError, chown_func, first_param, t(uid), gid)
            check_stat(uid, gid)
            self.assertRaises(TypeError, chown_func, first_param, uid, t(gid))
            check_stat(uid, gid)

    @unittest.skipUnless(hasattr(os, "chown"), "requires os.chown()")
    @unittest.skipIf(support.is_emscripten, "getgid() is a stub")
    def test_chown(self):
        # raise an OSError if the file does not exist
        os.unlink(os_helper.TESTFN)
        self.assertRaises(OSError, posix.chown, os_helper.TESTFN, -1, -1)

        # re-create the file
        os_helper.create_empty_file(os_helper.TESTFN)
        self._test_all_chown_common(posix.chown, os_helper.TESTFN, posix.stat)

    @os_helper.skip_unless_working_chmod
    @unittest.skipUnless(hasattr(posix, 'fchown'), "test needs os.fchown()")
    @unittest.skipIf(support.is_emscripten, "getgid() is a stub")
    def test_fchown(self):
        os.unlink(os_helper.TESTFN)

        # re-create the file
        test_file = open(os_helper.TESTFN, 'w')
        try:
            fd = test_file.fileno()
            self._test_all_chown_common(posix.fchown, fd,
                                        getattr(posix, 'fstat', None))
        finally:
            test_file.close()

    @os_helper.skip_unless_working_chmod
    @unittest.skipUnless(hasattr(posix, 'lchown'), "test needs os.lchown()")
    def test_lchown(self):
        os.unlink(os_helper.TESTFN)
        # create a symlink
        os.symlink(_DUMMY_SYMLINK, os_helper.TESTFN)
        self._test_all_chown_common(posix.lchown, os_helper.TESTFN,
                                    getattr(posix, 'lstat', None))

    @unittest.skipUnless(hasattr(posix, 'chdir'), 'test needs posix.chdir()')
    def test_chdir(self):
        posix.chdir(os.curdir)
        self.assertRaises(OSError, posix.chdir, os_helper.TESTFN)

    def test_listdir(self):
        self.assertIn(os_helper.TESTFN, posix.listdir(os.curdir))

    def test_listdir_default(self):
        # When listdir is called without argument,
        # it's the same as listdir(os.curdir).
        self.assertIn(os_helper.TESTFN, posix.listdir())

    def test_listdir_bytes(self):
        # When listdir is called with a bytes object,
        # the returned strings are of type bytes.
        self.assertIn(os.fsencode(os_helper.TESTFN), posix.listdir(b'.'))

    def test_listdir_bytes_like(self):
        for cls in bytearray, memoryview:
            with self.assertRaises(TypeError):
                posix.listdir(cls(b'.'))

    @unittest.skipUnless(posix.listdir in os.supports_fd,
                         "test needs fd support for posix.listdir()")
    def test_listdir_fd(self):
        f = posix.open(posix.getcwd(), posix.O_RDONLY)
        self.addCleanup(posix.close, f)
        self.assertEqual(
            sorted(posix.listdir('.')),
            sorted(posix.listdir(f))
            )
        # Check that the fd offset was reset (issue #13739)
        self.assertEqual(
            sorted(posix.listdir('.')),
            sorted(posix.listdir(f))
            )

    @unittest.skipUnless(hasattr(posix, 'access'), 'test needs posix.access()')
    def test_access(self):
        self.assertTrue(posix.access(os_helper.TESTFN, os.R_OK))

    @unittest.skipUnless(hasattr(posix, 'umask'), 'test needs posix.umask()')
    def test_umask(self):
        old_mask = posix.umask(0)
        self.assertIsInstance(old_mask, int)
        posix.umask(old_mask)

    @unittest.skipUnless(hasattr(posix, 'strerror'),
                         'test needs posix.strerror()')
    def test_strerror(self):
        self.assertTrue(posix.strerror(0))

    @unittest.skipUnless(hasattr(posix, 'pipe'), 'test needs posix.pipe()')
    def test_pipe(self):
        reader, writer = posix.pipe()
        os.close(reader)
        os.close(writer)

    @unittest.skipUnless(hasattr(os, 'pipe2'), "test needs os.pipe2()")
    @support.requires_linux_version(2, 6, 27)
    def test_pipe2(self):
        self.assertRaises(TypeError, os.pipe2, 'DEADBEEF')
        self.assertRaises(TypeError, os.pipe2, 0, 0)

        # try calling with flags = 0, like os.pipe()
        r, w = os.pipe2(0)
        os.close(r)
        os.close(w)

        # test flags
        r, w = os.pipe2(os.O_CLOEXEC|os.O_NONBLOCK)
        self.addCleanup(os.close, r)
        self.addCleanup(os.close, w)
        self.assertFalse(os.get_inheritable(r))
        self.assertFalse(os.get_inheritable(w))
        self.assertFalse(os.get_blocking(r))
        self.assertFalse(os.get_blocking(w))
        # try reading from an empty pipe: this should fail, not block
        self.assertRaises(OSError, os.read, r, 1)
        # try a write big enough to fill-up the pipe: this should either
        # fail or perform a partial write, not block
        try:
            os.write(w, b'x' * support.PIPE_MAX_SIZE)
        except OSError:
            pass

    @support.cpython_only
    @unittest.skipUnless(hasattr(os, 'pipe2'), "test needs os.pipe2()")
    @support.requires_linux_version(2, 6, 27)
    def test_pipe2_c_limits(self):
        # Issue 15989
        import _testcapi
        self.assertRaises(OverflowError, os.pipe2, _testcapi.INT_MAX + 1)
        self.assertRaises(OverflowError, os.pipe2, _testcapi.UINT_MAX + 1)

    @unittest.skipUnless(hasattr(posix, 'utime'), 'test needs posix.utime()')
    def test_utime(self):
        now = time.time()
        posix.utime(os_helper.TESTFN, None)
        self.assertRaises(TypeError, posix.utime,
                          os_helper.TESTFN, (None, None))
        self.assertRaises(TypeError, posix.utime,
                          os_helper.TESTFN, (now, None))
        self.assertRaises(TypeError, posix.utime,
                          os_helper.TESTFN, (None, now))
        posix.utime(os_helper.TESTFN, (int(now), int(now)))
        posix.utime(os_helper.TESTFN, (now, now))

    def check_chmod(self, chmod_func, target, **kwargs):
        closefd = not isinstance(target, int)
        mode = os.stat(target).st_mode
        try:
            new_mode = mode & ~(stat.S_IWOTH | stat.S_IWGRP | stat.S_IWUSR)
            chmod_func(target, new_mode, **kwargs)
            self.assertEqual(os.stat(target).st_mode, new_mode)
            if stat.S_ISREG(mode):
                try:
                    with open(target, 'wb+', closefd=closefd):
                        pass
                except PermissionError:
                    pass
            new_mode = mode | (stat.S_IWOTH | stat.S_IWGRP | stat.S_IWUSR)
            chmod_func(target, new_mode, **kwargs)
            self.assertEqual(os.stat(target).st_mode, new_mode)
            if stat.S_ISREG(mode):
                with open(target, 'wb+', closefd=closefd):
                    pass
        finally:
            chmod_func(target, mode)

    @os_helper.skip_unless_working_chmod
    def test_chmod_file(self):
        self.check_chmod(posix.chmod, os_helper.TESTFN)

    def tempdir(self):
        target = os_helper.TESTFN + 'd'
        posix.mkdir(target)
        self.addCleanup(posix.rmdir, target)
        return target

    @os_helper.skip_unless_working_chmod
    def test_chmod_dir(self):
        target = self.tempdir()
        self.check_chmod(posix.chmod, target)

    @os_helper.skip_unless_working_chmod
    def test_fchmod_file(self):
        with open(os_helper.TESTFN, 'wb+') as f:
            self.check_chmod(posix.fchmod, f.fileno())
            self.check_chmod(posix.chmod, f.fileno())

    @unittest.skipUnless(hasattr(posix, 'lchmod'), 'test needs os.lchmod()')
    def test_lchmod_file(self):
        self.check_chmod(posix.lchmod, os_helper.TESTFN)
        self.check_chmod(posix.chmod, os_helper.TESTFN, follow_symlinks=False)

    @unittest.skipUnless(hasattr(posix, 'lchmod'), 'test needs os.lchmod()')
    def test_lchmod_dir(self):
        target = self.tempdir()
        self.check_chmod(posix.lchmod, target)
        self.check_chmod(posix.chmod, target, follow_symlinks=False)

    def check_chmod_link(self, chmod_func, target, link, **kwargs):
        target_mode = os.stat(target).st_mode
        link_mode = os.lstat(link).st_mode
        try:
            new_mode = target_mode & ~(stat.S_IWOTH | stat.S_IWGRP | stat.S_IWUSR)
            chmod_func(link, new_mode, **kwargs)
            self.assertEqual(os.stat(target).st_mode, new_mode)
            self.assertEqual(os.lstat(link).st_mode, link_mode)
            new_mode = target_mode | (stat.S_IWOTH | stat.S_IWGRP | stat.S_IWUSR)
            chmod_func(link, new_mode, **kwargs)
            self.assertEqual(os.stat(target).st_mode, new_mode)
            self.assertEqual(os.lstat(link).st_mode, link_mode)
        finally:
            posix.chmod(target, target_mode)

    def check_lchmod_link(self, chmod_func, target, link, **kwargs):
        target_mode = os.stat(target).st_mode
        link_mode = os.lstat(link).st_mode
        new_mode = link_mode & ~(stat.S_IWOTH | stat.S_IWGRP | stat.S_IWUSR)
        chmod_func(link, new_mode, **kwargs)
        self.assertEqual(os.stat(target).st_mode, target_mode)
        self.assertEqual(os.lstat(link).st_mode, new_mode)
        new_mode = link_mode | (stat.S_IWOTH | stat.S_IWGRP | stat.S_IWUSR)
        chmod_func(link, new_mode, **kwargs)
        self.assertEqual(os.stat(target).st_mode, target_mode)
        self.assertEqual(os.lstat(link).st_mode, new_mode)

    @os_helper.skip_unless_symlink
    def test_chmod_file_symlink(self):
        target = os_helper.TESTFN
        link = os_helper.TESTFN + '-link'
        os.symlink(target, link)
        self.addCleanup(posix.unlink, link)
        if os.name == 'nt':
            self.check_lchmod_link(posix.chmod, target, link)
        else:
            self.check_chmod_link(posix.chmod, target, link)
        self.check_chmod_link(posix.chmod, target, link, follow_symlinks=True)

    @os_helper.skip_unless_symlink
    def test_chmod_dir_symlink(self):
        target = self.tempdir()
        link = os_helper.TESTFN + '-link'
        os.symlink(target, link, target_is_directory=True)
        self.addCleanup(posix.unlink, link)
        if os.name == 'nt':
            self.check_lchmod_link(posix.chmod, target, link)
        else:
            self.check_chmod_link(posix.chmod, target, link)
        self.check_chmod_link(posix.chmod, target, link, follow_symlinks=True)

    @unittest.skipUnless(hasattr(posix, 'lchmod'), 'test needs os.lchmod()')
    @os_helper.skip_unless_symlink
    def test_lchmod_file_symlink(self):
        target = os_helper.TESTFN
        link = os_helper.TESTFN + '-link'
        os.symlink(target, link)
        self.addCleanup(posix.unlink, link)
        self.check_lchmod_link(posix.chmod, target, link, follow_symlinks=False)
        self.check_lchmod_link(posix.lchmod, target, link)

    @unittest.skipUnless(hasattr(posix, 'lchmod'), 'test needs os.lchmod()')
    @os_helper.skip_unless_symlink
    def test_lchmod_dir_symlink(self):
        target = self.tempdir()
        link = os_helper.TESTFN + '-link'
        os.symlink(target, link)
        self.addCleanup(posix.unlink, link)
        self.check_lchmod_link(posix.chmod, target, link, follow_symlinks=False)
        self.check_lchmod_link(posix.lchmod, target, link)

    def _test_chflags_regular_file(self, chflags_func, target_file, **kwargs):
        st = os.stat(target_file)
        self.assertTrue(hasattr(st, 'st_flags'))

        # ZFS returns EOPNOTSUPP when attempting to set flag UF_IMMUTABLE.
        flags = st.st_flags | stat.UF_IMMUTABLE
        try:
            chflags_func(target_file, flags, **kwargs)
        except OSError as err:
            if err.errno != errno.EOPNOTSUPP:
                raise
            msg = 'chflag UF_IMMUTABLE not supported by underlying fs'
            self.skipTest(msg)

        try:
            new_st = os.stat(target_file)
            self.assertEqual(st.st_flags | stat.UF_IMMUTABLE, new_st.st_flags)
            try:
                fd = open(target_file, 'w+')
            except OSError as e:
                self.assertEqual(e.errno, errno.EPERM)
        finally:
            posix.chflags(target_file, st.st_flags)

    @unittest.skipUnless(hasattr(posix, 'chflags'), 'test needs os.chflags()')
    def test_chflags(self):
        self._test_chflags_regular_file(posix.chflags, os_helper.TESTFN)

    @unittest.skipUnless(hasattr(posix, 'lchflags'), 'test needs os.lchflags()')
    def test_lchflags_regular_file(self):
        self._test_chflags_regular_file(posix.lchflags, os_helper.TESTFN)
        self._test_chflags_regular_file(posix.chflags, os_helper.TESTFN,
                                        follow_symlinks=False)

    @unittest.skipUnless(hasattr(posix, 'lchflags'), 'test needs os.lchflags()')
    def test_lchflags_symlink(self):
        testfn_st = os.stat(os_helper.TESTFN)

        self.assertTrue(hasattr(testfn_st, 'st_flags'))

        self.addCleanup(os_helper.unlink, _DUMMY_SYMLINK)
        os.symlink(os_helper.TESTFN, _DUMMY_SYMLINK)
        dummy_symlink_st = os.lstat(_DUMMY_SYMLINK)

        def chflags_nofollow(path, flags):
            return posix.chflags(path, flags, follow_symlinks=False)

        for fn in (posix.lchflags, chflags_nofollow):
            # ZFS returns EOPNOTSUPP when attempting to set flag UF_IMMUTABLE.
            flags = dummy_symlink_st.st_flags | stat.UF_IMMUTABLE
            try:
                fn(_DUMMY_SYMLINK, flags)
            except OSError as err:
                if err.errno != errno.EOPNOTSUPP:
                    raise
                msg = 'chflag UF_IMMUTABLE not supported by underlying fs'
                self.skipTest(msg)
            try:
                new_testfn_st = os.stat(os_helper.TESTFN)
                new_dummy_symlink_st = os.lstat(_DUMMY_SYMLINK)

                self.assertEqual(testfn_st.st_flags, new_testfn_st.st_flags)
                self.assertEqual(dummy_symlink_st.st_flags | stat.UF_IMMUTABLE,
                                 new_dummy_symlink_st.st_flags)
            finally:
                fn(_DUMMY_SYMLINK, dummy_symlink_st.st_flags)

    def test_environ(self):
        if os.name == "nt":
            item_type = str
        else:
            item_type = bytes
        for k, v in posix.environ.items():
            self.assertEqual(type(k), item_type)
            self.assertEqual(type(v), item_type)

    def test_putenv(self):
        with self.assertRaises(ValueError):
            os.putenv('FRUIT\0VEGETABLE', 'cabbage')
        with self.assertRaises(ValueError):
            os.putenv('FRUIT', 'orange\0VEGETABLE=cabbage')
        with self.assertRaises(ValueError):
            os.putenv('FRUIT=ORANGE', 'lemon')
        if os.name == 'posix':
            with self.assertRaises(ValueError):
                os.putenv(b'FRUIT\0VEGETABLE', b'cabbage')
            with self.assertRaises(ValueError):
                os.putenv(b'FRUIT', b'orange\0VEGETABLE=cabbage')
            with self.assertRaises(ValueError):
                os.putenv(b'FRUIT=ORANGE', b'lemon')

    @unittest.skipUnless(hasattr(posix, 'getcwd'), 'test needs posix.getcwd()')
    def test_getcwd_long_pathnames(self):
        dirname = 'getcwd-test-directory-0123456789abcdef-01234567890abcdef'
        curdir = os.getcwd()
        base_path = os.path.abspath(os_helper.TESTFN) + '.getcwd'

        try:
            os.mkdir(base_path)
            os.chdir(base_path)
        except:
            #  Just returning nothing instead of the SkipTest exception, because
            #  the test results in Error in that case.  Is that ok?
            #  raise unittest.SkipTest("cannot create directory for testing")
            return

            def _create_and_do_getcwd(dirname, current_path_length = 0):
                try:
                    os.mkdir(dirname)
                except:
                    raise unittest.SkipTest("mkdir cannot create directory sufficiently deep for getcwd test")

                os.chdir(dirname)
                try:
                    os.getcwd()
                    if current_path_length < 1027:
                        _create_and_do_getcwd(dirname, current_path_length + len(dirname) + 1)
                finally:
                    os.chdir('..')
                    os.rmdir(dirname)

            _create_and_do_getcwd(dirname)

        finally:
            os.chdir(curdir)
            os_helper.rmtree(base_path)

    @unittest.skipUnless(hasattr(posix, 'getgrouplist'), "test needs posix.getgrouplist()")
    @unittest.skipUnless(hasattr(pwd, 'getpwuid'), "test needs pwd.getpwuid()")
    @unittest.skipUnless(hasattr(os, 'getuid'), "test needs os.getuid()")
    def test_getgrouplist(self):
        user = pwd.getpwuid(os.getuid())[0]
        group = pwd.getpwuid(os.getuid())[3]
        self.assertIn(group, posix.getgrouplist(user, group))


    @unittest.skipUnless(hasattr(os, 'getegid'), "test needs os.getegid()")
    @unittest.skipUnless(hasattr(os, 'popen'), "test needs os.popen()")
    @support.requires_subprocess()
    def test_getgroups(self):
        with os.popen('id -G 2>/dev/null') as idg:
            groups = idg.read().strip()
            ret = idg.close()

        try:
            idg_groups = set(int(g) for g in groups.split())
        except ValueError:
            idg_groups = set()
        if ret is not None or not idg_groups:
            raise unittest.SkipTest("need working 'id -G'")

        # Issues 16698: OS X ABIs prior to 10.6 have limits on getgroups()
        if sys.platform == 'darwin':
            import sysconfig
            dt = sysconfig.get_config_var('MACOSX_DEPLOYMENT_TARGET') or '10.3'
            if tuple(int(n) for n in dt.split('.')[0:2]) < (10, 6):
                raise unittest.SkipTest("getgroups(2) is broken prior to 10.6")

        # 'id -G' and 'os.getgroups()' should return the same
        # groups, ignoring order, duplicates, and the effective gid.
        # #10822/#26944 - It is implementation defined whether
        # posix.getgroups() includes the effective gid.
        symdiff = idg_groups.symmetric_difference(posix.getgroups())
        self.assertTrue(not symdiff or symdiff == {posix.getegid()})

    @unittest.skipUnless(hasattr(signal, 'SIGCHLD'), 'CLD_XXXX be placed in si_code for a SIGCHLD signal')
    @unittest.skipUnless(hasattr(os, 'waitid_result'), "test needs os.waitid_result")
    def test_cld_xxxx_constants(self):
        os.CLD_EXITED
        os.CLD_KILLED
        os.CLD_DUMPED
        os.CLD_TRAPPED
        os.CLD_STOPPED
        os.CLD_CONTINUED

    requires_sched_h = unittest.skipUnless(hasattr(posix, 'sched_yield'),
                                           "don't have scheduling support")
    requires_sched_affinity = unittest.skipUnless(hasattr(posix, 'sched_setaffinity'),
                                                  "don't have sched affinity support")

    @requires_sched_h
    def test_sched_yield(self):
        # This has no error conditions (at least on Linux).
        posix.sched_yield()

    @requires_sched_h
    @unittest.skipUnless(hasattr(posix, 'sched_get_priority_max'),
                         "requires sched_get_priority_max()")
    def test_sched_priority(self):
        # Round-robin usually has interesting priorities.
        pol = posix.SCHED_RR
        lo = posix.sched_get_priority_min(pol)
        hi = posix.sched_get_priority_max(pol)
        self.assertIsInstance(lo, int)
        self.assertIsInstance(hi, int)
        self.assertGreaterEqual(hi, lo)
        # Apple plaforms return 15 without checking the argument.
        if not is_apple:
            self.assertRaises(OSError, posix.sched_get_priority_min, -23)
            self.assertRaises(OSError, posix.sched_get_priority_max, -23)

    @requires_sched
    def test_get_and_set_scheduler_and_param(self):
        possible_schedulers = [sched for name, sched in posix.__dict__.items()
                               if name.startswith("SCHED_")]
        mine = posix.sched_getscheduler(0)
        self.assertIn(mine, possible_schedulers)
        try:
            parent = posix.sched_getscheduler(os.getppid())
        except PermissionError:
            # POSIX specifies EPERM, but Android returns EACCES. Both errno
            # values are mapped to PermissionError.
            pass
        else:
            self.assertIn(parent, possible_schedulers)
        self.assertRaises(OSError, posix.sched_getscheduler, -1)
        self.assertRaises(OSError, posix.sched_getparam, -1)
        param = posix.sched_getparam(0)
        self.assertIsInstance(param.sched_priority, int)

        # POSIX states that calling sched_setparam() or sched_setscheduler() on
        # a process with a scheduling policy other than SCHED_FIFO or SCHED_RR
        # is implementation-defined: NetBSD and FreeBSD can return EINVAL.
        if not sys.platform.startswith(('freebsd', 'netbsd')):
            try:
                posix.sched_setscheduler(0, mine, param)
                posix.sched_setparam(0, param)
            except PermissionError:
                pass
            self.assertRaises(OSError, posix.sched_setparam, -1, param)

        self.assertRaises(OSError, posix.sched_setscheduler, -1, mine, param)
        self.assertRaises(TypeError, posix.sched_setscheduler, 0, mine, None)
        self.assertRaises(TypeError, posix.sched_setparam, 0, 43)
        param = posix.sched_param(None)
        self.assertRaises(TypeError, posix.sched_setparam, 0, param)
        large = 214748364700
        param = posix.sched_param(large)
        self.assertRaises(OverflowError, posix.sched_setparam, 0, param)
        param = posix.sched_param(sched_priority=-large)
        self.assertRaises(OverflowError, posix.sched_setparam, 0, param)

    @unittest.skipUnless(hasattr(posix, "sched_rr_get_interval"), "no function")
    def test_sched_rr_get_interval(self):
        try:
            interval = posix.sched_rr_get_interval(0)
        except OSError as e:
            # This likely means that sched_rr_get_interval is only valid for
            # processes with the SCHED_RR scheduler in effect.
            if e.errno != errno.EINVAL:
                raise
            self.skipTest("only works on SCHED_RR processes")
        self.assertIsInstance(interval, float)
        # Reasonable constraints, I think.
        self.assertGreaterEqual(interval, 0.)
        self.assertLess(interval, 1.)

    @requires_sched_affinity
    def test_sched_getaffinity(self):
        mask = posix.sched_getaffinity(0)
        self.assertIsInstance(mask, set)
        self.assertGreaterEqual(len(mask), 1)
        if not sys.platform.startswith("freebsd"):
            # bpo-47205: does not raise OSError on FreeBSD
            self.assertRaises(OSError, posix.sched_getaffinity, -1)
        for cpu in mask:
            self.assertIsInstance(cpu, int)
            self.assertGreaterEqual(cpu, 0)
            self.assertLess(cpu, 1 << 32)

    @requires_sched_affinity
    def test_sched_setaffinity(self):
        mask = posix.sched_getaffinity(0)
        self.addCleanup(posix.sched_setaffinity, 0, list(mask))

        if len(mask) > 1:
            # Empty masks are forbidden
            mask.pop()
        posix.sched_setaffinity(0, mask)
        self.assertEqual(posix.sched_getaffinity(0), mask)

        try:
            posix.sched_setaffinity(0, [])
            # gh-117061: On RHEL9, sched_setaffinity(0, []) does not fail
        except OSError:
            # sched_setaffinity() manual page documents EINVAL error
            # when the mask is empty.
            pass

        self.assertRaises(ValueError, posix.sched_setaffinity, 0, [-10])
        self.assertRaises(ValueError, posix.sched_setaffinity, 0, map(int, "0X"))
        self.assertRaises(OverflowError, posix.sched_setaffinity, 0, [1<<128])
        if not sys.platform.startswith("freebsd"):
            # bpo-47205: does not raise OSError on FreeBSD
            self.assertRaises(OSError, posix.sched_setaffinity, -1, mask)

    @unittest.skipIf(support.is_wasi, "No dynamic linking on WASI")
    @unittest.skipUnless(os.name == 'posix', "POSIX-only test")
    def test_rtld_constants(self):
        # check presence of major RTLD_* constants
        posix.RTLD_LAZY
        posix.RTLD_NOW
        posix.RTLD_GLOBAL
        posix.RTLD_LOCAL

    @unittest.skipUnless(hasattr(os, 'SEEK_HOLE'),
                         "test needs an OS that reports file holes")
    def test_fs_holes(self):
        # Even if the filesystem doesn't report holes,
        # if the OS supports it the SEEK_* constants
        # will be defined and will have a consistent
        # behaviour:
        # os.SEEK_DATA = current position
        # os.SEEK_HOLE = end of file position
        with open(os_helper.TESTFN, 'r+b') as fp:
            fp.write(b"hello")
            fp.flush()
            size = fp.tell()
            fno = fp.fileno()
            try :
                for i in range(size):
                    self.assertEqual(i, os.lseek(fno, i, os.SEEK_DATA))
                    self.assertLessEqual(size, os.lseek(fno, i, os.SEEK_HOLE))
                self.assertRaises(OSError, os.lseek, fno, size, os.SEEK_DATA)
                self.assertRaises(OSError, os.lseek, fno, size, os.SEEK_HOLE)
            except OSError :
                # Some OSs claim to support SEEK_HOLE/SEEK_DATA
                # but it is not true.
                # For instance:
                # http://lists.freebsd.org/pipermail/freebsd-amd64/2012-January/014332.html
                raise unittest.SkipTest("OSError raised!")

    def test_path_error2(self):
        """
        Test functions that call path_error2(), providing two filenames in their exceptions.
        """
        for name in ("rename", "replace", "link"):
            function = getattr(os, name, None)
            if function is None:
                continue

            for dst in ("noodly2", os_helper.TESTFN):
                try:
                    function('doesnotexistfilename', dst)
                except OSError as e:
                    self.assertIn("'doesnotexistfilename' -> '{}'".format(dst), str(e))
                    break
            else:
                self.fail("No valid path_error2() test for os." + name)

    def test_path_with_null_character(self):
        fn = os_helper.TESTFN
        fn_with_NUL = fn + '\0'
        self.addCleanup(os_helper.unlink, fn)
        os_helper.unlink(fn)
        fd = None
        try:
            with self.assertRaises(ValueError):
                fd = os.open(fn_with_NUL, os.O_WRONLY | os.O_CREAT) # raises
        finally:
            if fd is not None:
                os.close(fd)
        self.assertFalse(os.path.exists(fn))
        self.assertRaises(ValueError, os.mkdir, fn_with_NUL)
        self.assertFalse(os.path.exists(fn))
        open(fn, 'wb').close()
        self.assertRaises(ValueError, os.stat, fn_with_NUL)

    def test_path_with_null_byte(self):
        fn = os.fsencode(os_helper.TESTFN)
        fn_with_NUL = fn + b'\0'
        self.addCleanup(os_helper.unlink, fn)
        os_helper.unlink(fn)
        fd = None
        try:
            with self.assertRaises(ValueError):
                fd = os.open(fn_with_NUL, os.O_WRONLY | os.O_CREAT) # raises
        finally:
            if fd is not None:
                os.close(fd)
        self.assertFalse(os.path.exists(fn))
        self.assertRaises(ValueError, os.mkdir, fn_with_NUL)
        self.assertFalse(os.path.exists(fn))
        open(fn, 'wb').close()
        self.assertRaises(ValueError, os.stat, fn_with_NUL)

    @unittest.skipUnless(hasattr(os, "pidfd_open"), "pidfd_open unavailable")
    def test_pidfd_open(self):
        with self.assertRaises(OSError) as cm:
            os.pidfd_open(-1)
        if cm.exception.errno == errno.ENOSYS:
            self.skipTest("system does not support pidfd_open")
        if isinstance(cm.exception, PermissionError):
            self.skipTest(f"pidfd_open syscall blocked: {cm.exception!r}")
        self.assertEqual(cm.exception.errno, errno.EINVAL)
        os.close(os.pidfd_open(os.getpid(), 0))


# tests for the posix *at functions follow
class TestPosixDirFd(unittest.TestCase):
    count = 0

    @contextmanager
    def prepare(self):
        TestPosixDirFd.count += 1
        name = f'{os_helper.TESTFN}_{self.count}'
        base_dir = f'{os_helper.TESTFN}_{self.count}base'
        posix.mkdir(base_dir)
        self.addCleanup(posix.rmdir, base_dir)
        fullname = os.path.join(base_dir, name)
        assert not os.path.exists(fullname)
        with os_helper.open_dir_fd(base_dir) as dir_fd:
            yield (dir_fd, name, fullname)

    @contextmanager
    def prepare_file(self):
        with self.prepare() as (dir_fd, name, fullname):
            os_helper.create_empty_file(fullname)
            self.addCleanup(posix.unlink, fullname)
            yield (dir_fd, name, fullname)

    @unittest.skipUnless(os.access in os.supports_dir_fd, "test needs dir_fd support for os.access()")
    def test_access_dir_fd(self):
        with self.prepare_file() as (dir_fd, name, fullname):
            self.assertTrue(posix.access(name, os.R_OK, dir_fd=dir_fd))

    @unittest.skipUnless(os.chmod in os.supports_dir_fd, "test needs dir_fd support in os.chmod()")
    def test_chmod_dir_fd(self):
        with self.prepare_file() as (dir_fd, name, fullname):
            posix.chmod(fullname, stat.S_IRUSR)
            posix.chmod(name, stat.S_IRUSR | stat.S_IWUSR, dir_fd=dir_fd)
            s = posix.stat(fullname)
            self.assertEqual(s.st_mode & stat.S_IRWXU,
                             stat.S_IRUSR | stat.S_IWUSR)

    @unittest.skipUnless(hasattr(os, 'chown') and (os.chown in os.supports_dir_fd),
                         "test needs dir_fd support in os.chown()")
    @unittest.skipIf(support.is_emscripten, "getgid() is a stub")
    def test_chown_dir_fd(self):
        with self.prepare_file() as (dir_fd, name, fullname):
            posix.chown(name, os.getuid(), os.getgid(), dir_fd=dir_fd)

    @unittest.skipUnless(os.stat in os.supports_dir_fd, "test needs dir_fd support in os.stat()")
    def test_stat_dir_fd(self):
        with self.prepare() as (dir_fd, name, fullname):
            with open(fullname, 'w') as outfile:
                outfile.write("testline\n")
            self.addCleanup(posix.unlink, fullname)

            s1 = posix.stat(fullname)
            s2 = posix.stat(name, dir_fd=dir_fd)
            self.assertEqual(s1, s2)
            s2 = posix.stat(fullname, dir_fd=None)
            self.assertEqual(s1, s2)

            self.assertRaisesRegex(TypeError, 'should be integer or None, not',
                    posix.stat, name, dir_fd=posix.getcwd())
            self.assertRaisesRegex(TypeError, 'should be integer or None, not',
                    posix.stat, name, dir_fd=float(dir_fd))
            self.assertRaises(OverflowError,
                    posix.stat, name, dir_fd=10**20)

            for fd in False, True:
                with self.assertWarnsRegex(RuntimeWarning,
                        'bool is used as a file descriptor') as cm:
                    with self.assertRaises(OSError):
                        posix.stat('nonexisting', dir_fd=fd)
                self.assertEqual(cm.filename, __file__)

    @unittest.skipUnless(os.utime in os.supports_dir_fd, "test needs dir_fd support in os.utime()")
    def test_utime_dir_fd(self):
        with self.prepare_file() as (dir_fd, name, fullname):
            now = time.time()
            posix.utime(name, None, dir_fd=dir_fd)
            posix.utime(name, dir_fd=dir_fd)
            self.assertRaises(TypeError, posix.utime, name,
                              now, dir_fd=dir_fd)
            self.assertRaises(TypeError, posix.utime, name,
                              (None, None), dir_fd=dir_fd)
            self.assertRaises(TypeError, posix.utime, name,
                              (now, None), dir_fd=dir_fd)
            self.assertRaises(TypeError, posix.utime, name,
                              (None, now), dir_fd=dir_fd)
            self.assertRaises(TypeError, posix.utime, name,
                              (now, "x"), dir_fd=dir_fd)
            posix.utime(name, (int(now), int(now)), dir_fd=dir_fd)
            posix.utime(name, (now, now), dir_fd=dir_fd)
            posix.utime(name,
                    (int(now), int((now - int(now)) * 1e9)), dir_fd=dir_fd)
            posix.utime(name, dir_fd=dir_fd,
                            times=(int(now), int((now - int(now)) * 1e9)))

            # try dir_fd and follow_symlinks together
            if os.utime in os.supports_follow_symlinks:
                try:
                    posix.utime(name, follow_symlinks=False, dir_fd=dir_fd)
                except ValueError:
                    # whoops!  using both together not supported on this platform.
                    pass

    @unittest.skipIf(
        support.is_wasi,
        "WASI: symlink following on path_link is not supported"
    )
    @unittest.skipUnless(
        hasattr(os, "link") and os.link in os.supports_dir_fd,
        "test needs dir_fd support in os.link()"
    )
    def test_link_dir_fd(self):
        with self.prepare_file() as (dir_fd, name, fullname), \
             self.prepare() as (dir_fd2, linkname, fulllinkname):
            try:
                posix.link(name, linkname, src_dir_fd=dir_fd, dst_dir_fd=dir_fd2)
            except PermissionError as e:
                self.skipTest('posix.link(): %s' % e)
            self.addCleanup(posix.unlink, fulllinkname)
            # should have same inodes
            self.assertEqual(posix.stat(fullname)[1],
                posix.stat(fulllinkname)[1])

    @unittest.skipUnless(os.mkdir in os.supports_dir_fd, "test needs dir_fd support in os.mkdir()")
    def test_mkdir_dir_fd(self):
        with self.prepare() as (dir_fd, name, fullname):
            posix.mkdir(name, dir_fd=dir_fd)
            self.addCleanup(posix.rmdir, fullname)
            posix.stat(fullname) # should not raise exception

    @unittest.skipUnless(hasattr(os, 'mknod')
                         and (os.mknod in os.supports_dir_fd)
                         and hasattr(stat, 'S_IFIFO'),
                         "test requires both stat.S_IFIFO and dir_fd support for os.mknod()")
    def test_mknod_dir_fd(self):
        # Test using mknodat() to create a FIFO (the only use specified
        # by POSIX).
        with self.prepare() as (dir_fd, name, fullname):
            mode = stat.S_IFIFO | stat.S_IRUSR | stat.S_IWUSR
            try:
                posix.mknod(name, mode, 0, dir_fd=dir_fd)
            except OSError as e:
                # Some old systems don't allow unprivileged users to use
                # mknod(), or only support creating device nodes.
                self.assertIn(e.errno, (errno.EPERM, errno.EINVAL, errno.EACCES))
            else:
                self.addCleanup(posix.unlink, fullname)
                self.assertTrue(stat.S_ISFIFO(posix.stat(fullname).st_mode))

    @unittest.skipUnless(os.open in os.supports_dir_fd, "test needs dir_fd support in os.open()")
    def test_open_dir_fd(self):
        with self.prepare() as (dir_fd, name, fullname):
            with open(fullname, 'wb') as outfile:
                outfile.write(b"testline\n")
            self.addCleanup(posix.unlink, fullname)
            fd = posix.open(name, posix.O_RDONLY, dir_fd=dir_fd)
            try:
                res = posix.read(fd, 9)
                self.assertEqual(b"testline\n", res)
            finally:
                posix.close(fd)

    @unittest.skipUnless(hasattr(os, 'readlink') and (os.readlink in os.supports_dir_fd),
                         "test needs dir_fd support in os.readlink()")
    def test_readlink_dir_fd(self):
        with self.prepare() as (dir_fd, name, fullname):
            os.symlink('symlink', fullname)
            self.addCleanup(posix.unlink, fullname)
            self.assertEqual(posix.readlink(name, dir_fd=dir_fd), 'symlink')

    @unittest.skipUnless(os.rename in os.supports_dir_fd, "test needs dir_fd support in os.rename()")
    def test_rename_dir_fd(self):
        with self.prepare_file() as (dir_fd, name, fullname), \
             self.prepare() as (dir_fd2, name2, fullname2):
            posix.rename(name, name2,
                         src_dir_fd=dir_fd, dst_dir_fd=dir_fd2)
            posix.stat(fullname2) # should not raise exception
            posix.rename(fullname2, fullname)

    @unittest.skipUnless(os.symlink in os.supports_dir_fd, "test needs dir_fd support in os.symlink()")
    def test_symlink_dir_fd(self):
        with self.prepare() as (dir_fd, name, fullname):
            posix.symlink('symlink', name, dir_fd=dir_fd)
            self.addCleanup(posix.unlink, fullname)
            self.assertEqual(posix.readlink(fullname), 'symlink')

    @unittest.skipUnless(os.unlink in os.supports_dir_fd, "test needs dir_fd support in os.unlink()")
    def test_unlink_dir_fd(self):
        with self.prepare() as (dir_fd, name, fullname):
            os_helper.create_empty_file(fullname)
            posix.stat(fullname) # should not raise exception
            try:
                posix.unlink(name, dir_fd=dir_fd)
                self.assertRaises(OSError, posix.stat, fullname)
            except:
                self.addCleanup(posix.unlink, fullname)
                raise

    @unittest.skipUnless(hasattr(os, 'mkfifo') and os.mkfifo in os.supports_dir_fd, "test needs dir_fd support in os.mkfifo()")
    def test_mkfifo_dir_fd(self):
        with self.prepare() as (dir_fd, name, fullname):
            try:
                posix.mkfifo(name, stat.S_IRUSR | stat.S_IWUSR, dir_fd=dir_fd)
            except PermissionError as e:
                self.skipTest('posix.mkfifo(): %s' % e)
            self.addCleanup(posix.unlink, fullname)
            self.assertTrue(stat.S_ISFIFO(posix.stat(fullname).st_mode))


class PosixGroupsTester(unittest.TestCase):

    def setUp(self):
        if posix.getuid() != 0:
            raise unittest.SkipTest("not enough privileges")
        if not hasattr(posix, 'getgroups'):
            raise unittest.SkipTest("need posix.getgroups")
        if sys.platform == 'darwin':
            raise unittest.SkipTest("getgroups(2) is broken on OSX")
        self.saved_groups = posix.getgroups()

    def tearDown(self):
        if hasattr(posix, 'setgroups'):
            posix.setgroups(self.saved_groups)
        elif hasattr(posix, 'initgroups'):
            name = pwd.getpwuid(posix.getuid()).pw_name
            posix.initgroups(name, self.saved_groups[0])

    @unittest.skipUnless(hasattr(posix, 'initgroups'),
                         "test needs posix.initgroups()")
    def test_initgroups(self):
        # find missing group

        g = max(self.saved_groups or [0]) + 1
        name = pwd.getpwuid(posix.getuid()).pw_name
        posix.initgroups(name, g)
        self.assertIn(g, posix.getgroups())

    @unittest.skipUnless(hasattr(posix, 'setgroups'),
                         "test needs posix.setgroups()")
    def test_setgroups(self):
        for groups in [[0], list(range(16))]:
            posix.setgroups(groups)
            self.assertListEqual(groups, posix.getgroups())


class _PosixSpawnMixin:
    # Program which does nothing and exits with status 0 (success)
    NOOP_PROGRAM = (sys.executable, '-I', '-S', '-c', 'pass')
    spawn_func = None

    def python_args(self, *args):
        # Disable site module to avoid side effects. For example,
        # on Fedora 28, if the HOME environment variable is not set,
        # site._getuserbase() calls pwd.getpwuid() which opens
        # /var/lib/sss/mc/passwd but then leaves the file open which makes
        # test_close_file() to fail.
        return (sys.executable, '-I', '-S', *args)

    def test_returns_pid(self):
        pidfile = os_helper.TESTFN
        self.addCleanup(os_helper.unlink, pidfile)
        script = f"""if 1:
            import os
            with open({pidfile!r}, "w") as pidfile:
                pidfile.write(str(os.getpid()))
            """
        args = self.python_args('-c', script)
        pid = self.spawn_func(args[0], args, os.environ)
        support.wait_process(pid, exitcode=0)
        with open(pidfile, encoding="utf-8") as f:
            self.assertEqual(f.read(), str(pid))

    def test_no_such_executable(self):
        no_such_executable = 'no_such_executable'
        try:
            pid = self.spawn_func(no_such_executable,
                                  [no_such_executable],
                                  os.environ)
        # bpo-35794: PermissionError can be raised if there are
        # directories in the $PATH that are not accessible.
        except (FileNotFoundError, PermissionError) as exc:
            self.assertEqual(exc.filename, no_such_executable)
        else:
            pid2, status = os.waitpid(pid, 0)
            self.assertEqual(pid2, pid)
            self.assertNotEqual(status, 0)

    def test_specify_environment(self):
        envfile = os_helper.TESTFN
        self.addCleanup(os_helper.unlink, envfile)
        script = f"""if 1:
            import os
            with open({envfile!r}, "w", encoding="utf-8") as envfile:
                envfile.write(os.environ['foo'])
        """
        args = self.python_args('-c', script)
        pid = self.spawn_func(args[0], args,
                              {**os.environ, 'foo': 'bar'})
        support.wait_process(pid, exitcode=0)
        with open(envfile, encoding="utf-8") as f:
            self.assertEqual(f.read(), 'bar')

    def test_none_file_actions(self):
        pid = self.spawn_func(
            self.NOOP_PROGRAM[0],
            self.NOOP_PROGRAM,
            os.environ,
            file_actions=None
        )
        support.wait_process(pid, exitcode=0)

    def test_empty_file_actions(self):
        pid = self.spawn_func(
            self.NOOP_PROGRAM[0],
            self.NOOP_PROGRAM,
            os.environ,
            file_actions=[]
        )
        support.wait_process(pid, exitcode=0)

    def test_resetids_explicit_default(self):
        pid = self.spawn_func(
            sys.executable,
            [sys.executable, '-c', 'pass'],
            os.environ,
            resetids=False
        )
        support.wait_process(pid, exitcode=0)

    def test_resetids(self):
        pid = self.spawn_func(
            sys.executable,
            [sys.executable, '-c', 'pass'],
            os.environ,
            resetids=True
        )
        support.wait_process(pid, exitcode=0)

    def test_setpgroup(self):
        pid = self.spawn_func(
            sys.executable,
            [sys.executable, '-c', 'pass'],
            os.environ,
            setpgroup=os.getpgrp()
        )
        support.wait_process(pid, exitcode=0)

    def test_setpgroup_wrong_type(self):
        with self.assertRaises(TypeError):
            self.spawn_func(sys.executable,
                            [sys.executable, "-c", "pass"],
                            os.environ, setpgroup="023")

    @unittest.skipUnless(hasattr(signal, 'pthread_sigmask'),
                           'need signal.pthread_sigmask()')
    def test_setsigmask(self):
        code = textwrap.dedent("""\
            import signal
            signal.raise_signal(signal.SIGUSR1)""")

        pid = self.spawn_func(
            sys.executable,
            [sys.executable, '-c', code],
            os.environ,
            setsigmask=[signal.SIGUSR1]
        )
        support.wait_process(pid, exitcode=0)

    def test_setsigmask_wrong_type(self):
        with self.assertRaises(TypeError):
            self.spawn_func(sys.executable,
                            [sys.executable, "-c", "pass"],
                            os.environ, setsigmask=34)
        with self.assertRaises(TypeError):
            self.spawn_func(sys.executable,
                            [sys.executable, "-c", "pass"],
                            os.environ, setsigmask=["j"])
        with self.assertRaises(ValueError):
            self.spawn_func(sys.executable,
                            [sys.executable, "-c", "pass"],
                            os.environ, setsigmask=[signal.NSIG,
                                                    signal.NSIG+1])

    def test_setsid(self):
        rfd, wfd = os.pipe()
        self.addCleanup(os.close, rfd)
        try:
            os.set_inheritable(wfd, True)

            code = textwrap.dedent(f"""
                import os
                fd = {wfd}
                sid = os.getsid(0)
                os.write(fd, str(sid).encode())
            """)

            try:
                pid = self.spawn_func(sys.executable,
                                      [sys.executable, "-c", code],
                                      os.environ, setsid=True)
            except NotImplementedError as exc:
                self.skipTest(f"setsid is not supported: {exc!r}")
            except PermissionError as exc:
                self.skipTest(f"setsid failed with: {exc!r}")
        finally:
            os.close(wfd)

        support.wait_process(pid, exitcode=0)

        output = os.read(rfd, 100)
        child_sid = int(output)
        parent_sid = os.getsid(os.getpid())
        self.assertNotEqual(parent_sid, child_sid)

    @unittest.skipUnless(hasattr(signal, 'pthread_sigmask'),
                         'need signal.pthread_sigmask()')
    def test_setsigdef(self):
        original_handler = signal.signal(signal.SIGUSR1, signal.SIG_IGN)
        code = textwrap.dedent("""\
            import signal
            signal.raise_signal(signal.SIGUSR1)""")
        try:
            pid = self.spawn_func(
                sys.executable,
                [sys.executable, '-c', code],
                os.environ,
                setsigdef=[signal.SIGUSR1]
            )
        finally:
            signal.signal(signal.SIGUSR1, original_handler)

        support.wait_process(pid, exitcode=-signal.SIGUSR1)

    def test_setsigdef_wrong_type(self):
        with self.assertRaises(TypeError):
            self.spawn_func(sys.executable,
                            [sys.executable, "-c", "pass"],
                            os.environ, setsigdef=34)
        with self.assertRaises(TypeError):
            self.spawn_func(sys.executable,
                            [sys.executable, "-c", "pass"],
                            os.environ, setsigdef=["j"])
        with self.assertRaises(ValueError):
            self.spawn_func(sys.executable,
                            [sys.executable, "-c", "pass"],
                            os.environ, setsigdef=[signal.NSIG, signal.NSIG+1])

    @requires_sched
    @unittest.skipIf(sys.platform.startswith(('freebsd', 'netbsd')),
                     "bpo-34685: test can fail on BSD")
    def test_setscheduler_only_param(self):
        policy = os.sched_getscheduler(0)
        priority = os.sched_get_priority_min(policy)
        code = textwrap.dedent(f"""\
            import os, sys
            if os.sched_getscheduler(0) != {policy}:
                sys.exit(101)
            if os.sched_getparam(0).sched_priority != {priority}:
                sys.exit(102)""")
        pid = self.spawn_func(
            sys.executable,
            [sys.executable, '-c', code],
            os.environ,
            scheduler=(None, os.sched_param(priority))
        )
        support.wait_process(pid, exitcode=0)

    @requires_sched
    @unittest.skipIf(sys.platform.startswith(('freebsd', 'netbsd')),
                     "bpo-34685: test can fail on BSD")
    def test_setscheduler_with_policy(self):
        policy = os.sched_getscheduler(0)
        priority = os.sched_get_priority_min(policy)
        code = textwrap.dedent(f"""\
            import os, sys
            if os.sched_getscheduler(0) != {policy}:
                sys.exit(101)
            if os.sched_getparam(0).sched_priority != {priority}:
                sys.exit(102)""")
        pid = self.spawn_func(
            sys.executable,
            [sys.executable, '-c', code],
            os.environ,
            scheduler=(policy, os.sched_param(priority))
        )
        support.wait_process(pid, exitcode=0)

    def test_multiple_file_actions(self):
        file_actions = [
            (os.POSIX_SPAWN_OPEN, 3, os.path.realpath(__file__), os.O_RDONLY, 0),
            (os.POSIX_SPAWN_CLOSE, 0),
            (os.POSIX_SPAWN_DUP2, 1, 4),
        ]
        pid = self.spawn_func(self.NOOP_PROGRAM[0],
                              self.NOOP_PROGRAM,
                              os.environ,
                              file_actions=file_actions)
        support.wait_process(pid, exitcode=0)

    def test_bad_file_actions(self):
        args = self.NOOP_PROGRAM
        with self.assertRaises(TypeError):
            self.spawn_func(args[0], args, os.environ,
                            file_actions=[None])
        with self.assertRaises(TypeError):
            self.spawn_func(args[0], args, os.environ,
                            file_actions=[()])
        with self.assertRaises(TypeError):
            self.spawn_func(args[0], args, os.environ,
                            file_actions=[(None,)])
        with self.assertRaises(TypeError):
            self.spawn_func(args[0], args, os.environ,
                            file_actions=[(12345,)])
        with self.assertRaises(TypeError):
            self.spawn_func(args[0], args, os.environ,
                            file_actions=[(os.POSIX_SPAWN_CLOSE,)])
        with self.assertRaises(TypeError):
            self.spawn_func(args[0], args, os.environ,
                            file_actions=[(os.POSIX_SPAWN_CLOSE, 1, 2)])
        with self.assertRaises(TypeError):
            self.spawn_func(args[0], args, os.environ,
                            file_actions=[(os.POSIX_SPAWN_CLOSE, None)])
        with self.assertRaises(ValueError):
            self.spawn_func(args[0], args, os.environ,
                            file_actions=[(os.POSIX_SPAWN_OPEN,
                                           3, __file__ + '\0',
                                           os.O_RDONLY, 0)])

    def test_open_file(self):
        outfile = os_helper.TESTFN
        self.addCleanup(os_helper.unlink, outfile)
        script = """if 1:
            import sys
            sys.stdout.write("hello")
            """
        file_actions = [
            (os.POSIX_SPAWN_OPEN, 1, outfile,
                os.O_WRONLY | os.O_CREAT | os.O_TRUNC,
                stat.S_IRUSR | stat.S_IWUSR),
        ]
        args = self.python_args('-c', script)
        pid = self.spawn_func(args[0], args, os.environ,
                              file_actions=file_actions)

        support.wait_process(pid, exitcode=0)
        with open(outfile, encoding="utf-8") as f:
            self.assertEqual(f.read(), 'hello')

    def test_close_file(self):
        closefile = os_helper.TESTFN
        self.addCleanup(os_helper.unlink, closefile)
        script = f"""if 1:
            import os
            try:
                os.fstat(0)
            except OSError as e:
                with open({closefile!r}, 'w', encoding='utf-8') as closefile:
                    closefile.write('is closed %d' % e.errno)
            """
        args = self.python_args('-c', script)
        pid = self.spawn_func(args[0], args, os.environ,
                              file_actions=[(os.POSIX_SPAWN_CLOSE, 0)])

        support.wait_process(pid, exitcode=0)
        with open(closefile, encoding="utf-8") as f:
            self.assertEqual(f.read(), 'is closed %d' % errno.EBADF)

    def test_dup2(self):
        dupfile = os_helper.TESTFN
        self.addCleanup(os_helper.unlink, dupfile)
        script = """if 1:
            import sys
            sys.stdout.write("hello")
            """
        with open(dupfile, "wb") as childfile:
            file_actions = [
                (os.POSIX_SPAWN_DUP2, childfile.fileno(), 1),
            ]
            args = self.python_args('-c', script)
            pid = self.spawn_func(args[0], args, os.environ,
                                  file_actions=file_actions)
            support.wait_process(pid, exitcode=0)
        with open(dupfile, encoding="utf-8") as f:
            self.assertEqual(f.read(), 'hello')


@unittest.skipUnless(hasattr(os, 'posix_spawn'), "test needs os.posix_spawn")
@support.requires_subprocess()
class TestPosixSpawn(unittest.TestCase, _PosixSpawnMixin):
    spawn_func = getattr(posix, 'posix_spawn', None)


@unittest.skipUnless(hasattr(os, 'posix_spawnp'), "test needs os.posix_spawnp")
@support.requires_subprocess()
class TestPosixSpawnP(unittest.TestCase, _PosixSpawnMixin):
    spawn_func = getattr(posix, 'posix_spawnp', None)

    @os_helper.skip_unless_symlink
    def test_posix_spawnp(self):
        # Use a symlink to create a program in its own temporary directory
        temp_dir = tempfile.mkdtemp()
        self.addCleanup(os_helper.rmtree, temp_dir)

        program = 'posix_spawnp_test_program.exe'
        program_fullpath = os.path.join(temp_dir, program)
        os.symlink(sys.executable, program_fullpath)

        try:
            path = os.pathsep.join((temp_dir, os.environ['PATH']))
        except KeyError:
            path = temp_dir   # PATH is not set

        spawn_args = (program, '-I', '-S', '-c', 'pass')
        code = textwrap.dedent("""
            import os
            from test import support

            args = %a
            pid = os.posix_spawnp(args[0], args, os.environ)

            support.wait_process(pid, exitcode=0)
        """ % (spawn_args,))

        # Use a subprocess to test os.posix_spawnp() with a modified PATH
        # environment variable: posix_spawnp() uses the current environment
        # to locate the program, not its environment argument.
        args = ('-c', code)
        assert_python_ok(*args, PATH=path)


@unittest.skipUnless(sys.platform == "darwin", "test weak linking on macOS")
class TestPosixWeaklinking(unittest.TestCase):
    # These test cases verify that weak linking support on macOS works
    # as expected. These cases only test new behaviour introduced by weak linking,
    # regular behaviour is tested by the normal test cases.
    #
    # See the section on Weak Linking in Mac/README.txt for more information.
    def setUp(self):
        import sysconfig
        import platform

        config_vars = sysconfig.get_config_vars()
        self.available = { nm for nm in config_vars if nm.startswith("HAVE_") and config_vars[nm] }
        self.mac_ver = tuple(int(part) for part in platform.mac_ver()[0].split("."))

    def _verify_available(self, name):
        if name not in self.available:
            raise unittest.SkipTest(f"{name} not weak-linked")

    def test_pwritev(self):
        self._verify_available("HAVE_PWRITEV")
        if self.mac_ver >= (10, 16):
            self.assertTrue(hasattr(os, "pwritev"), "os.pwritev is not available")
            self.assertTrue(hasattr(os, "preadv"), "os.readv is not available")

        else:
            self.assertFalse(hasattr(os, "pwritev"), "os.pwritev is available")
            self.assertFalse(hasattr(os, "preadv"), "os.readv is available")

    def test_stat(self):
        self._verify_available("HAVE_FSTATAT")
        if self.mac_ver >= (10, 10):
            self.assertIn("HAVE_FSTATAT", posix._have_functions)

        else:
            self.assertNotIn("HAVE_FSTATAT", posix._have_functions)

            with self.assertRaisesRegex(NotImplementedError, "dir_fd unavailable"):
                os.stat("file", dir_fd=0)

    def test_ptsname_r(self):
        self._verify_available("HAVE_PTSNAME_R")
        if self.mac_ver >= (10, 13, 4):
            self.assertIn("HAVE_PTSNAME_R", posix._have_functions)
        else:
            self.assertNotIn("HAVE_PTSNAME_R", posix._have_functions)

    def test_access(self):
        self._verify_available("HAVE_FACCESSAT")
        if self.mac_ver >= (10, 10):
            self.assertIn("HAVE_FACCESSAT", posix._have_functions)

        else:
            self.assertNotIn("HAVE_FACCESSAT", posix._have_functions)

            with self.assertRaisesRegex(NotImplementedError, "dir_fd unavailable"):
                os.access("file", os.R_OK, dir_fd=0)

            with self.assertRaisesRegex(NotImplementedError, "follow_symlinks unavailable"):
                os.access("file", os.R_OK, follow_symlinks=False)

            with self.assertRaisesRegex(NotImplementedError, "effective_ids unavailable"):
                os.access("file", os.R_OK, effective_ids=True)

    def test_chmod(self):
        self._verify_available("HAVE_FCHMODAT")
        if self.mac_ver >= (10, 10):
            self.assertIn("HAVE_FCHMODAT", posix._have_functions)

        else:
            self.assertNotIn("HAVE_FCHMODAT", posix._have_functions)
            self.assertIn("HAVE_LCHMOD", posix._have_functions)

            with self.assertRaisesRegex(NotImplementedError, "dir_fd unavailable"):
                os.chmod("file", 0o644, dir_fd=0)

    def test_chown(self):
        self._verify_available("HAVE_FCHOWNAT")
        if self.mac_ver >= (10, 10):
            self.assertIn("HAVE_FCHOWNAT", posix._have_functions)

        else:
            self.assertNotIn("HAVE_FCHOWNAT", posix._have_functions)
            self.assertIn("HAVE_LCHOWN", posix._have_functions)

            with self.assertRaisesRegex(NotImplementedError, "dir_fd unavailable"):
                os.chown("file", 0, 0, dir_fd=0)

    def test_link(self):
        self._verify_available("HAVE_LINKAT")
        if self.mac_ver >= (10, 10):
            self.assertIn("HAVE_LINKAT", posix._have_functions)

        else:
            self.assertNotIn("HAVE_LINKAT", posix._have_functions)

            with self.assertRaisesRegex(NotImplementedError, "src_dir_fd unavailable"):
                os.link("source", "target",  src_dir_fd=0)

            with self.assertRaisesRegex(NotImplementedError, "dst_dir_fd unavailable"):
                os.link("source", "target",  dst_dir_fd=0)

            with self.assertRaisesRegex(NotImplementedError, "src_dir_fd unavailable"):
                os.link("source", "target",  src_dir_fd=0, dst_dir_fd=0)

            # issue 41355: !HAVE_LINKAT code path ignores the follow_symlinks flag
            with os_helper.temp_dir() as base_path:
                link_path = os.path.join(base_path, "link")
                target_path = os.path.join(base_path, "target")
                source_path = os.path.join(base_path, "source")

                with open(source_path, "w") as fp:
                    fp.write("data")

                os.symlink("target", link_path)

                # Calling os.link should fail in the link(2) call, and
                # should not reject *follow_symlinks* (to match the
                # behaviour you'd get when building on a platform without
                # linkat)
                with self.assertRaises(FileExistsError):
                    os.link(source_path, link_path, follow_symlinks=True)

                with self.assertRaises(FileExistsError):
                    os.link(source_path, link_path, follow_symlinks=False)


    def test_listdir_scandir(self):
        self._verify_available("HAVE_FDOPENDIR")
        if self.mac_ver >= (10, 10):
            self.assertIn("HAVE_FDOPENDIR", posix._have_functions)

        else:
            self.assertNotIn("HAVE_FDOPENDIR", posix._have_functions)

            with self.assertRaisesRegex(TypeError, "listdir: path should be string, bytes, os.PathLike or None, not int"):
                os.listdir(0)

            with self.assertRaisesRegex(TypeError, "scandir: path should be string, bytes, os.PathLike or None, not int"):
                os.scandir(0)

    def test_mkdir(self):
        self._verify_available("HAVE_MKDIRAT")
        if self.mac_ver >= (10, 10):
            self.assertIn("HAVE_MKDIRAT", posix._have_functions)

        else:
            self.assertNotIn("HAVE_MKDIRAT", posix._have_functions)

            with self.assertRaisesRegex(NotImplementedError, "dir_fd unavailable"):
                os.mkdir("dir", dir_fd=0)

    def test_mkfifo(self):
        self._verify_available("HAVE_MKFIFOAT")
        if self.mac_ver >= (13, 0):
            self.assertIn("HAVE_MKFIFOAT", posix._have_functions)

        else:
            self.assertNotIn("HAVE_MKFIFOAT", posix._have_functions)

            with self.assertRaisesRegex(NotImplementedError, "dir_fd unavailable"):
                os.mkfifo("path", dir_fd=0)

    def test_mknod(self):
        self._verify_available("HAVE_MKNODAT")
        if self.mac_ver >= (13, 0):
            self.assertIn("HAVE_MKNODAT", posix._have_functions)

        else:
            self.assertNotIn("HAVE_MKNODAT", posix._have_functions)

            with self.assertRaisesRegex(NotImplementedError, "dir_fd unavailable"):
                os.mknod("path", dir_fd=0)

    def test_rename_replace(self):
        self._verify_available("HAVE_RENAMEAT")
        if self.mac_ver >= (10, 10):
            self.assertIn("HAVE_RENAMEAT", posix._have_functions)

        else:
            self.assertNotIn("HAVE_RENAMEAT", posix._have_functions)

            with self.assertRaisesRegex(NotImplementedError, "src_dir_fd and dst_dir_fd unavailable"):
                os.rename("a", "b", src_dir_fd=0)

            with self.assertRaisesRegex(NotImplementedError, "src_dir_fd and dst_dir_fd unavailable"):
                os.rename("a", "b", dst_dir_fd=0)

            with self.assertRaisesRegex(NotImplementedError, "src_dir_fd and dst_dir_fd unavailable"):
                os.replace("a", "b", src_dir_fd=0)

            with self.assertRaisesRegex(NotImplementedError, "src_dir_fd and dst_dir_fd unavailable"):
                os.replace("a", "b", dst_dir_fd=0)

    def test_unlink_rmdir(self):
        self._verify_available("HAVE_UNLINKAT")
        if self.mac_ver >= (10, 10):
            self.assertIn("HAVE_UNLINKAT", posix._have_functions)

        else:
            self.assertNotIn("HAVE_UNLINKAT", posix._have_functions)

            with self.assertRaisesRegex(NotImplementedError, "dir_fd unavailable"):
                os.unlink("path", dir_fd=0)

            with self.assertRaisesRegex(NotImplementedError, "dir_fd unavailable"):
                os.rmdir("path", dir_fd=0)

    def test_open(self):
        self._verify_available("HAVE_OPENAT")
        if self.mac_ver >= (10, 10):
            self.assertIn("HAVE_OPENAT", posix._have_functions)

        else:
            self.assertNotIn("HAVE_OPENAT", posix._have_functions)

            with self.assertRaisesRegex(NotImplementedError, "dir_fd unavailable"):
                os.open("path", os.O_RDONLY, dir_fd=0)

    def test_readlink(self):
        self._verify_available("HAVE_READLINKAT")
        if self.mac_ver >= (10, 10):
            self.assertIn("HAVE_READLINKAT", posix._have_functions)

        else:
            self.assertNotIn("HAVE_READLINKAT", posix._have_functions)

            with self.assertRaisesRegex(NotImplementedError, "dir_fd unavailable"):
                os.readlink("path",  dir_fd=0)

    def test_symlink(self):
        self._verify_available("HAVE_SYMLINKAT")
        if self.mac_ver >= (10, 10):
            self.assertIn("HAVE_SYMLINKAT", posix._have_functions)

        else:
            self.assertNotIn("HAVE_SYMLINKAT", posix._have_functions)

            with self.assertRaisesRegex(NotImplementedError, "dir_fd unavailable"):
                os.symlink("a", "b",  dir_fd=0)

    def test_utime(self):
        self._verify_available("HAVE_FUTIMENS")
        self._verify_available("HAVE_UTIMENSAT")
        if self.mac_ver >= (10, 13):
            self.assertIn("HAVE_FUTIMENS", posix._have_functions)
            self.assertIn("HAVE_UTIMENSAT", posix._have_functions)

        else:
            self.assertNotIn("HAVE_FUTIMENS", posix._have_functions)
            self.assertNotIn("HAVE_UTIMENSAT", posix._have_functions)

            with self.assertRaisesRegex(NotImplementedError, "dir_fd unavailable"):
                os.utime("path", dir_fd=0)


class NamespacesTests(unittest.TestCase):
    """Tests for os.unshare() and os.setns()."""

    @unittest.skipUnless(hasattr(os, 'unshare'), 'needs os.unshare()')
    @unittest.skipUnless(hasattr(os, 'setns'), 'needs os.setns()')
    @unittest.skipUnless(os.path.exists('/proc/self/ns/uts'), 'need /proc/self/ns/uts')
    @support.requires_linux_version(3, 0, 0)
    def test_unshare_setns(self):
        code = """if 1:
            import errno
            import os
            import sys
            fd = os.open('/proc/self/ns/uts', os.O_RDONLY)
            try:
                original = os.readlink('/proc/self/ns/uts')
                try:
                    os.unshare(os.CLONE_NEWUTS)
                except OSError as e:
                    if e.errno == errno.ENOSPC:
                        # skip test if limit is exceeded
                        sys.exit()
                    raise
                new = os.readlink('/proc/self/ns/uts')
                if original == new:
                    raise Exception('os.unshare failed')
                os.setns(fd, os.CLONE_NEWUTS)
                restored = os.readlink('/proc/self/ns/uts')
                if original != restored:
                    raise Exception('os.setns failed')
            except PermissionError:
                # The calling process did not have the required privileges
                # for this operation
                pass
            except OSError as e:
                # Skip the test on these errors:
                # - ENOSYS: syscall not available
                # - EINVAL: kernel was not configured with the CONFIG_UTS_NS option
                # - ENOMEM: not enough memory
                if e.errno not in (errno.ENOSYS, errno.EINVAL, errno.ENOMEM):
                    raise
            finally:
                os.close(fd)
            """

        assert_python_ok("-c", code)


def tearDownModule():
    support.reap_children()


if __name__ == '__main__':
    unittest.main()