diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index a4c5fbb4815..3c4b0d52931 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -990,6 +990,17 @@ as internal buffering of data.
    .. versionadded:: 3.3
 
 
+.. function:: login_tty(fd)
+
+   Prepare the tty of which fd is a file descriptor for a new login session.
+   Make the calling process a session leader; make the tty the controlling tty,
+   the stdin, the stdout, and the stderr of the calling process; close fd.
+
+   .. availability:: Unix.
+
+   .. versionadded:: 3.10
+
+
 .. function:: lseek(fd, pos, how)
 
    Set the current position of file descriptor *fd* to position *pos*, modified
diff --git a/Misc/NEWS.d/next/Library/2020-12-11-04-56-12.bpo-41818.bVX3sO.rst b/Misc/NEWS.d/next/Library/2020-12-11-04-56-12.bpo-41818.bVX3sO.rst
new file mode 100644
index 00000000000..8fec11fbe4f
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-12-11-04-56-12.bpo-41818.bVX3sO.rst
@@ -0,0 +1 @@
+Soumendra Ganguly: New function os.login_tty() for Unix.
diff --git a/Modules/clinic/posixmodule.c.h b/Modules/clinic/posixmodule.c.h
index 4a72ea0dd56..5015da70b53 100644
--- a/Modules/clinic/posixmodule.c.h
+++ b/Modules/clinic/posixmodule.c.h
@@ -3029,6 +3029,41 @@ os_openpty(PyObject *module, PyObject *Py_UNUSED(ignored))
 
 #endif /* (defined(HAVE_OPENPTY) || defined(HAVE__GETPTY) || defined(HAVE_DEV_PTMX)) */
 
+#if (defined(HAVE_LOGIN_TTY) || defined(HAVE_FALLBACK_LOGIN_TTY))
+
+PyDoc_STRVAR(os_login_tty__doc__,
+"login_tty($module, fd, /)\n"
+"--\n"
+"\n"
+"Prepare the tty of which fd is a file descriptor for a new login session.\n"
+"\n"
+"Make the calling process a session leader; make the tty the\n"
+"controlling tty, the stdin, the stdout, and the stderr of the\n"
+"calling process; close fd.");
+
+#define OS_LOGIN_TTY_METHODDEF    \
+    {"login_tty", (PyCFunction)os_login_tty, METH_O, os_login_tty__doc__},
+
+static PyObject *
+os_login_tty_impl(PyObject *module, int fd);
+
+static PyObject *
+os_login_tty(PyObject *module, PyObject *arg)
+{
+    PyObject *return_value = NULL;
+    int fd;
+
+    if (!_PyLong_FileDescriptor_Converter(arg, &fd)) {
+        goto exit;
+    }
+    return_value = os_login_tty_impl(module, fd);
+
+exit:
+    return return_value;
+}
+
+#endif /* (defined(HAVE_LOGIN_TTY) || defined(HAVE_FALLBACK_LOGIN_TTY)) */
+
 #if defined(HAVE_FORKPTY)
 
 PyDoc_STRVAR(os_forkpty__doc__,
@@ -8764,6 +8799,10 @@ exit:
     #define OS_OPENPTY_METHODDEF
 #endif /* !defined(OS_OPENPTY_METHODDEF) */
 
+#ifndef OS_LOGIN_TTY_METHODDEF
+    #define OS_LOGIN_TTY_METHODDEF
+#endif /* !defined(OS_LOGIN_TTY_METHODDEF) */
+
 #ifndef OS_FORKPTY_METHODDEF
     #define OS_FORKPTY_METHODDEF
 #endif /* !defined(OS_FORKPTY_METHODDEF) */
@@ -9163,4 +9202,4 @@ exit:
 #ifndef OS_WAITSTATUS_TO_EXITCODE_METHODDEF
     #define OS_WAITSTATUS_TO_EXITCODE_METHODDEF
 #endif /* !defined(OS_WAITSTATUS_TO_EXITCODE_METHODDEF) */
-/*[clinic end generated code: output=f3ec08afcd6cd8f8 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=f9f9bf32d1318d82 input=a9049054013a1b77]*/
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index d9eb62f20e6..3e0530f7768 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -7118,22 +7118,21 @@ error:
 #  define DEV_PTY_FILE "/dev/ptmx"
 #endif
 
-#if defined(HAVE_OPENPTY) || defined(HAVE_FORKPTY) || defined(HAVE_DEV_PTMX)
-#ifdef HAVE_PTY_H
+#if defined(HAVE_OPENPTY) || defined(HAVE_FORKPTY) || defined(HAVE_LOGIN_TTY) || defined(HAVE_DEV_PTMX)
+#if defined(HAVE_PTY_H)
 #include <pty.h>
-#else
-#ifdef HAVE_LIBUTIL_H
+#if defined(HAVE_UTMP_H)
+#include <utmp.h>
+#endif /* HAVE_UTMP_H */
+#elif defined(HAVE_LIBUTIL_H)
 #include <libutil.h>
-#else
-#ifdef HAVE_UTIL_H
+#elif defined(HAVE_UTIL_H)
 #include <util.h>
-#endif /* HAVE_UTIL_H */
-#endif /* HAVE_LIBUTIL_H */
 #endif /* HAVE_PTY_H */
 #ifdef HAVE_STROPTS_H
 #include <stropts.h>
 #endif
-#endif /* defined(HAVE_OPENPTY) || defined(HAVE_FORKPTY) || defined(HAVE_DEV_PTMX) */
+#endif /* if defined(HAVE_OPENPTY) || defined(HAVE_FORKPTY) || defined(HAVE_LOGIN_TTY) || defined(HAVE_DEV_PTMX) */
 
 
 #if defined(HAVE_OPENPTY) || defined(HAVE__GETPTY) || defined(HAVE_DEV_PTMX)
@@ -7235,6 +7234,84 @@ error:
 }
 #endif /* defined(HAVE_OPENPTY) || defined(HAVE__GETPTY) || defined(HAVE_DEV_PTMX) */
 
+#if defined(HAVE_SETSID)
+#if defined(TIOCSCTTY) || defined(HAVE_TTYNAME)
+#define HAVE_FALLBACK_LOGIN_TTY 1
+#endif /* defined(TIOCSCTTY) || defined(HAVE_TTYNAME) */
+#endif /* HAVE_SETSID */
+
+#if defined(HAVE_LOGIN_TTY) || defined(HAVE_FALLBACK_LOGIN_TTY)
+/*[clinic input]
+os.login_tty
+
+    fd: fildes
+    /
+
+Prepare the tty of which fd is a file descriptor for a new login session.
+
+Make the calling process a session leader; make the tty the
+controlling tty, the stdin, the stdout, and the stderr of the
+calling process; close fd.
+[clinic start generated code]*/
+
+static PyObject *
+os_login_tty_impl(PyObject *module, int fd)
+/*[clinic end generated code: output=495a79911b4cc1bc input=5f298565099903a2]*/
+{
+#if defined(HAVE_LOGIN_TTY)
+    if (login_tty(fd) == -1) {
+        return posix_error();
+    }
+#else /* defined(HAVE_FALLBACK_LOGIN_TTY) */
+    /* Establish a new session. */
+    if (setsid() == -1) {
+        return posix_error();
+    }
+
+    /* The tty becomes the controlling terminal. */
+#if defined(TIOCSCTTY)
+    if (ioctl(fd, TIOCSCTTY, (char *)NULL) == -1) {
+        return posix_error();
+    }
+#else /* defined(HAVE_TTYNAME) */
+    /* Fallback method (archaic); from Advanced Programming in the UNIX(R)
+     * Environment, Third edition, 2013, Section 9.6 - Controlling Terminal:
+     * "Systems derived from UNIX System V allocate the controlling
+     * terminal for a session when the session leader opens the first
+     * terminal device that is not already associated with a session, as
+     * long as the call to open does not specify the O_NOCTTY flag." */
+    char *tmppath = ttyname(fd);
+    if (tmppath == NULL) {
+        return posix_error();
+    }
+
+#define CLOSE_IF_NOT_FD(otherfd) \
+    if (fd != otherfd) { \
+        close(otherfd); \
+    } \
+
+    CLOSE_IF_NOT_FD(0);
+    CLOSE_IF_NOT_FD(1);
+    CLOSE_IF_NOT_FD(2);
+
+    int tmpfd = open(tmppath, O_RDWR);
+    if (tmpfd == -1) {
+        return posix_error();
+    }
+    close(tmpfd);
+#endif /* defined(TIOCSCTTY) */
+
+    /* The tty becomes stdin/stdout/stderr */
+    if (dup2(fd, 0) == -1 || dup2(fd, 1) == -1 || dup2(fd, 2) == -1) {
+        return posix_error();
+    }
+    if (fd > 2) {
+        close(fd);
+    }
+#endif /* defined(HAVE_LOGIN_TTY) */
+    Py_RETURN_NONE;
+}
+#endif /* defined(HAVE_LOGIN_TTY) || defined(HAVE_FALLBACK_LOGIN_TTY) */
 
 #ifdef HAVE_FORKPTY
 /*[clinic input]
@@ -7271,8 +7348,9 @@ os_forkpty_impl(PyObject *module)
         /* parent: release the import lock. */
         PyOS_AfterFork_Parent();
     }
-    if (pid == -1)
+    if (pid == -1) {
         return posix_error();
+    }
     return Py_BuildValue("(Ni)", PyLong_FromPid(pid), master_fd);
 }
 #endif /* HAVE_FORKPTY */
@@ -7613,7 +7691,7 @@ os_initgroups_impl(PyObject *module, PyObject *oname, gid_t gid)
     const char *username = PyBytes_AS_STRING(oname);
 
     if (initgroups(username, gid) == -1)
-        return PyErr_SetFromErrno(PyExc_OSError);
+        return posix_error();
 
     Py_RETURN_NONE;
 }
@@ -14652,6 +14730,7 @@ static PyMethodDef posix_methods[] = {
     OS_SCHED_GETAFFINITY_METHODDEF
     OS_OPENPTY_METHODDEF
     OS_FORKPTY_METHODDEF
+    OS_LOGIN_TTY_METHODDEF
     OS_GETEGID_METHODDEF
     OS_GETEUID_METHODDEF
     OS_GETGID_METHODDEF
diff --git a/configure b/configure
index 9ee750b70f4..55eb94dc6df 100755
--- a/configure
+++ b/configure
@@ -8041,7 +8041,7 @@ sys/audioio.h sys/xattr.h sys/bsdtty.h sys/event.h sys/file.h sys/ioctl.h \
 sys/kern_control.h sys/loadavg.h sys/lock.h sys/mkdev.h sys/modem.h \
 sys/param.h sys/random.h sys/select.h sys/sendfile.h sys/socket.h sys/statvfs.h \
 sys/stat.h sys/syscall.h sys/sys_domain.h sys/termio.h sys/time.h \
-sys/times.h sys/types.h sys/uio.h sys/un.h sys/utsname.h sys/wait.h pty.h \
+sys/times.h sys/types.h sys/uio.h sys/un.h sys/utsname.h sys/wait.h pty.h utmp.h \
 libutil.h sys/resource.h netpacket/packet.h sysexits.h bluetooth.h \
 linux/tipc.h linux/random.h spawn.h util.h alloca.h endian.h \
 sys/endian.h sys/sysmacros.h linux/memfd.h linux/wait.h sys/memfd.h \
@@ -12735,7 +12735,7 @@ $as_echo "no" >&6; }
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 
-# check for openpty and forkpty
+# check for openpty, login_tty, and forkpty
 
 for ac_func in openpty
 do :
@@ -12831,6 +12831,103 @@ fi
 fi
 
 
+fi
+done
+
+for ac_func in login_tty
+do :
+  ac_fn_c_check_func "$LINENO" "login_tty" "ac_cv_func_login_tty"
+if test "x$ac_cv_func_login_tty" = xyes; then :
+  cat >>confdefs.h <<_ACEOF
+#define HAVE_LOGIN_TTY 1
+_ACEOF
+
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for login_tty in -lutil" >&5
+$as_echo_n "checking for login_tty in -lutil... " >&6; }
+if ${ac_cv_lib_util_login_tty+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  ac_check_lib_save_LIBS=$LIBS
+LIBS="-lutil  $LIBS"
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+/* Override any GCC internal prototype to avoid an error.
+   Use char because int might match the return type of a GCC
+   builtin and then its argument prototype would still apply.  */
+#ifdef __cplusplus
+extern "C"
+#endif
+char login_tty ();
+int
+main ()
+{
+return login_tty ();
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  ac_cv_lib_util_login_tty=yes
+else
+  ac_cv_lib_util_login_tty=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+LIBS=$ac_check_lib_save_LIBS
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_lib_util_login_tty" >&5
+$as_echo "$ac_cv_lib_util_login_tty" >&6; }
+if test "x$ac_cv_lib_util_login_tty" = xyes; then :
+  $as_echo "#define HAVE_LOGIN_TTY 1" >>confdefs.h
+ LIBS="$LIBS -lutil"
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for login_tty in -lbsd" >&5
+$as_echo_n "checking for login_tty in -lbsd... " >&6; }
+if ${ac_cv_lib_bsd_login_tty+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  ac_check_lib_save_LIBS=$LIBS
+LIBS="-lbsd  $LIBS"
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+/* Override any GCC internal prototype to avoid an error.
+   Use char because int might match the return type of a GCC
+   builtin and then its argument prototype would still apply.  */
+#ifdef __cplusplus
+extern "C"
+#endif
+char login_tty ();
+int
+main ()
+{
+return login_tty ();
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  ac_cv_lib_bsd_login_tty=yes
+else
+  ac_cv_lib_bsd_login_tty=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+LIBS=$ac_check_lib_save_LIBS
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_lib_bsd_login_tty" >&5
+$as_echo "$ac_cv_lib_bsd_login_tty" >&6; }
+if test "x$ac_cv_lib_bsd_login_tty" = xyes; then :
+  $as_echo "#define HAVE_LOGIN_TTY 1" >>confdefs.h
+ LIBS="$LIBS -lbsd"
+fi
+
+
+fi
+
+
 fi
 done