"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 copy
import errno
import sys
import signal
import time
import os
import platform
import pickle
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()')
    def test_confstr(self):
        with self.assertRaisesRegex(
            ValueError, "unrecognized configuration name"
        ):
            posix.confstr("CS_garbage")

        with self.assertRaisesRegex(
            TypeError, "configuration names must be strings or integers"
        ):
            posix.confstr(1.23)

        path = posix.confstr("CS_PATH")
        self.assertGreater(len(path), 0)
        self.assertEqual(posix.confstr(posix.confstr_names["CS_PATH"]), path)

    @unittest.skipUnless(hasattr(posix, 'sysconf'),
                         'test needs posix.sysconf()')
    def test_sysconf(self):
        with self.assertRaisesRegex(
            ValueError, "unrecognized configuration name"
        ):
            posix.sysconf("SC_garbage")

        with self.assertRaisesRegex(
            TypeError, "configuration names must be strings or integers"
        ):
            posix.sysconf(1.23)

        arg_max = posix.sysconf("SC_ARG_MAX")
        self.assertGreater(arg_max, 0)
        self.assertEqual(
            posix.sysconf(posix.sysconf_names["SC_ARG_MAX"]), arg_max)

    @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()

    @unittest.skipUnless(hasattr(posix, 'stat'),
                         'test needs posix.stat()')
    @unittest.skipUnless(os.stat in os.supports_follow_symlinks,
                         'test needs follow_symlinks support in os.stat()')
    def test_stat_fd_zero_follow_symlinks(self):
        with self.assertRaisesRegex(ValueError,
                'cannot use fd and follow_symlinks together'):
            posix.stat(0, follow_symlinks=False)
        with self.assertRaisesRegex(ValueError,
                'cannot use fd and follow_symlinks together'):
            posix.stat(1, follow_symlinks=False)

    def check_statlike_path(self, func):
        self.assertTrue(func(os_helper.TESTFN))
        self.assertTrue(func(os.fsencode(os_helper.TESTFN)))
        self.assertTrue(func(os_helper.FakePath(os_helper.TESTFN)))

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

    def test_stat(self):
        self.check_statlike_path(posix.stat)

    @unittest.skipUnless(hasattr(posix, 'statx'), 'test needs posix.statx()')
    def test_statx(self):
        def func(path, **kwargs):
            return posix.statx(path, posix.STATX_BASIC_STATS, **kwargs)
        self.check_statlike_path(func)

    @unittest.skipUnless(hasattr(posix, 'statx'), 'test needs posix.statx()')
    def test_statx_flags(self):
        # glibc's fallback implementation of statx via the stat family fails
        # with EINVAL on the (nonzero) sync flags.  If you see this failure,
        # update your kernel and/or seccomp syscall filter.
        valid_flag_names = ('AT_NO_AUTOMOUNT', 'AT_STATX_SYNC_AS_STAT',
                            'AT_STATX_FORCE_SYNC', 'AT_STATX_DONT_SYNC')
        for flag_name in valid_flag_names:
            flag = getattr(posix, flag_name)
            with self.subTest(msg=flag_name, flags=flag):
                posix.statx(os_helper.TESTFN, posix.STATX_BASIC_STATS,
                            flags=flag)

        # These flags are not exposed to Python because their functionality is
        # implemented via kwargs instead.
        kwarg_equivalent_flags = (
            (0x0100, 'AT_SYMLINK_NOFOLLOW', 'follow_symlinks'),
            (0x0400, 'AT_SYMLINK_FOLLOW', 'follow_symlinks'),
            (0x1000, 'AT_EMPTY_PATH', 'dir_fd'),
        )
        for flag, flag_name, kwarg_name in kwarg_equivalent_flags:
            with self.subTest(msg=flag_name, flags=flag):
                with self.assertRaisesRegex(ValueError, kwarg_name):
                    posix.statx(os_helper.TESTFN, posix.STATX_BASIC_STATS,
                                flags=flag)

        with self.subTest(msg="AT_STATX_FORCE_SYNC | AT_STATX_DONT_SYNC"):
            with self.assertRaises(OSError) as ctx:
                flags = posix.AT_STATX_FORCE_SYNC | posix.AT_STATX_DONT_SYNC
                posix.statx(os_helper.TESTFN, posix.STATX_BASIC_STATS,
                            flags=flags)
            self.assertEqual(ctx.exception.errno, errno.EINVAL)

    @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)

        # The following tests are needed to test functions accepting or
        # returning the special value NODEV (if it is defined). major(), minor()
        # and makefile() are the only easily reproducible examples, but that
        # behavior is platform specific -- on some platforms their code has
        # a special case for NODEV, on others this is just an implementation
        # artifact.
        if (hasattr(posix, 'NODEV') and
            sys.platform.startswith(('linux', 'macos', 'freebsd', 'dragonfly',
                                     'sunos'))):
            NODEV = posix.NODEV
            self.assertEqual(posix.major(NODEV), NODEV)
            self.assertEqual(posix.minor(NODEV), NODEV)
            self.assertEqual(posix.makedev(NODEV, NODEV), NODEV)

    def test_nodev(self):
        # NODEV is not a part of Posix, but is defined on many systems.
        if (not hasattr(posix, 'NODEV')
            and (not sys.platform.startswith(('linux', 'macos', 'freebsd',
                                              'dragonfly', 'netbsd', 'openbsd',
                                              'sunos'))
                 or support.linked_to_musl())):
            self.skipTest('not defined on this platform')
        self.assertHasAttr(posix, '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.assertHasAttr(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.assertHasAttr(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 platforms 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)

    @requires_sched
    def test_sched_param(self):
        param = posix.sched_param(1)
        for proto in range(pickle.HIGHEST_PROTOCOL+1):
            newparam = pickle.loads(pickle.dumps(param, proto))
            self.assertEqual(newparam, param)
        newparam = copy.copy(param)
        self.assertIsNot(newparam, param)
        self.assertEqual(newparam, param)
        newparam = copy.deepcopy(param)
        self.assertIsNot(newparam, param)
        self.assertEqual(newparam, param)
        newparam = copy.replace(param)
        self.assertIsNot(newparam, param)
        self.assertEqual(newparam, param)
        newparam = copy.replace(param, sched_priority=0)
        self.assertNotEqual(newparam, param)
        self.assertEqual(newparam.sched_priority, 0)

    @requires_sched
    def test_bug_140634(self):
        sched_priority = float('inf')  # any new reference
        param = posix.sched_param(sched_priority)
        param.__reduce__()
        del sched_priority, param  # should not crash
        support.gc_collect()  # just to be sure

    @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))

    @os_helper.skip_unless_hardlink
    @os_helper.skip_unless_symlink
    def test_link_follow_symlinks(self):
        default_follow = sys.platform.startswith(
            ('darwin', 'freebsd', 'netbsd', 'openbsd', 'dragonfly', 'sunos5'))
        default_no_follow = sys.platform.startswith(('win32', 'linux'))
        orig = os_helper.TESTFN
        symlink = orig + 'symlink'
        posix.symlink(orig, symlink)
        self.addCleanup(os_helper.unlink, symlink)

        with self.subTest('no follow_symlinks'):
            # no follow_symlinks -> platform depending
            link = orig + 'link'
            posix.link(symlink, link)
            self.addCleanup(os_helper.unlink, link)
            if os.link in os.supports_follow_symlinks or default_follow:
                self.assertEqual(posix.lstat(link), posix.lstat(orig))
            elif default_no_follow:
                self.assertEqual(posix.lstat(link), posix.lstat(symlink))

        with self.subTest('follow_symlinks=False'):
            # follow_symlinks=False -> duplicate the symlink itself
            link = orig + 'link_nofollow'
            try:
                posix.link(symlink, link, follow_symlinks=False)
            except NotImplementedError:
                if os.link in os.supports_follow_symlinks or default_no_follow:
                    raise
            else:
                self.addCleanup(os_helper.unlink, link)
                self.assertEqual(posix.lstat(link), posix.lstat(symlink))

        with self.subTest('follow_symlinks=True'):
            # follow_symlinks=True -> duplicate the target file
            link = orig + 'link_following'
            try:
                posix.link(symlink, link, follow_symlinks=True)
            except NotImplementedError:
                if os.link in os.supports_follow_symlinks or default_follow:
                    raise
            else:
                self.addCleanup(os_helper.unlink, link)
                self.assertEqual(posix.lstat(link), posix.lstat(orig))


# 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)

    def check_statlike_dir_fd(self, func, prefix):
        with self.prepare() as (dir_fd, name, fullname):
            with open(fullname, 'w') as outfile:
                outfile.write("testline\n")
            self.addCleanup(posix.unlink, fullname)

            def get(result, attr):
                return getattr(result, prefix + attr)

            s1 = func(fullname)
            s2 = func(name, dir_fd=dir_fd)
            self.assertEqual((get(s1, "dev"), get(s1, "ino")),
                             (get(s2, "dev"), get(s2, "ino")))
            s2 = func(fullname, dir_fd=None)
            self.assertEqual((get(s1, "dev"), get(s1, "ino")),
                             (get(s2, "dev"), get(s2, "ino")))

            self.assertRaisesRegex(TypeError, 'should be integer or None, not',
                    func, name, dir_fd=posix.getcwd())
            self.assertRaisesRegex(TypeError, 'should be integer or None, not',
                    func, name, dir_fd=float(dir_fd))
            self.assertRaises(OverflowError,
                    func, 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):
                        func('nonexisting', dir_fd=fd)
                self.assertEqual(cm.filename, __file__)

    @unittest.skipUnless(os.stat in os.supports_dir_fd, "test needs dir_fd support in os.stat()")
    def test_stat_dir_fd(self):
        self.check_statlike_dir_fd(posix.stat, prefix="st_")

    @unittest.skipUnless(hasattr(posix, 'statx'), "test needs os.statx()")
    def test_statx_dir_fd(self):
        def func(path, **kwargs):
            return posix.statx(path, os.STATX_INO, **kwargs)
        self.check_statlike_dir_fd(func, prefix="stx_")

    @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")
    @unittest.skipIf(platform.libc_ver()[0] == 'glibc' and
                     os.sched_getscheduler(0) in [
                        os.SCHED_BATCH,
                        os.SCHED_IDLE,
                        os.SCHED_DEADLINE],
                     "Skip test due to glibc posix_spawn policy")
    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.assertHasAttr(os, "pwritev")
            self.assertHasAttr(os, "preadv")

        else:
            self.assertNotHasAttr(os, "pwritev")
            self.assertNotHasAttr(os, "preadv")

    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()
