diff --git a/ChangeLog b/ChangeLog
index 8ad03354a0..77af307f40 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+Sat Nov 24 11:47:14 2012  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* process.c (proc_getsid): adds new method for getting session id.
+	  Contributed from fumiyas (Fumiyasu SATOH). Thank you!
+	  [Feature #6757] [ruby-dev:45977]
+	* configure.in: adds getsid check.
+	* test/ruby/test_process.rb (TestProcess#test_setsid): new test
+	  for the above.
+	* NEWS: news for the above.
+
 Sat Nov 24 10:59:14 2012  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* thread.c (thread_create_core): don't use th->thread_id before
diff --git a/NEWS b/NEWS
index 2fa1c32bf0..2da55a3c2a 100644
--- a/NEWS
+++ b/NEWS
@@ -109,6 +109,10 @@ with all sufficient information, see the ChangeLog file.
     * added method:
       * added nil.to_h which returns {}
 
+  * Process
+    * added method:
+      * added getsid for getting sessin id (unix only).
+
   * Range
     * added method:
       * added Range#size for lazy size evaluation.
diff --git a/configure.in b/configure.in
index d7d4a46660..7fa99c6d55 100644
--- a/configure.in
+++ b/configure.in
@@ -1554,7 +1554,7 @@ AC_CHECK_FUNCS(fmod killpg wait4 waitpid fork spawnv syscall __syscall chroot ge
 	      getpgrp setpgrp getpgid setpgid initgroups getgroups setgroups\
 	      getpriority getrlimit setrlimit sysconf close getpwnam_r getgrnam_r\
 	      dlopen sigprocmask sigaction sigsetjmp _setjmp _longjmp\
-	      setsid telldir seekdir fchmod cosh sinh tanh log2 round llabs\
+	      getsid setsid telldir seekdir fchmod cosh sinh tanh log2 round llabs\
 	      setuid setgid daemon select_large_fdset setenv unsetenv\
               mktime timegm gmtime_r clock_gettime gettimeofday poll ppoll\
               pread sendfile shutdown sigaltstack dl_iterate_phdr\
diff --git a/process.c b/process.c
index 427168de6c..1bda315b70 100644
--- a/process.c
+++ b/process.c
@@ -4219,6 +4219,40 @@ proc_setpgid(VALUE obj, VALUE pid, VALUE pgrp)
 #endif
 
 
+#ifdef HAVE_GETSID
+/*
+ *  call-seq:
+ *     Process.getsid()      -> integer
+ *     Process.getsid(pid)   -> integer
+ *
+ *  Returns the session ID for for the given process id. If not give,
+ *  return current process sid. Not available on all platforms.
+ *
+ *     Process.getsid()                #=> 27422
+ *     Process.getsid(0)               #=> 27422
+ *     Process.getsid(Process.pid())   #=> 27422
+ */
+static VALUE
+proc_getsid(int argc, VALUE *argv)
+{
+    rb_pid_t sid;
+    VALUE pid;
+
+    rb_secure(2);
+    rb_scan_args(argc, argv, "01", &pid);
+
+    if (NIL_P(pid))
+	pid = INT2NUM(0);
+
+    sid = getsid(NUM2PIDT(pid));
+    if (sid < 0) rb_sys_fail(0);
+    return PIDT2NUM(sid);
+}
+#else
+#define proc_getsid rb_f_notimplement
+#endif
+
+
 #if defined(HAVE_SETSID) || (defined(HAVE_SETPGRP) && defined(TIOCNOTTY))
 #if !defined(HAVE_SETSID)
 static rb_pid_t ruby_setsid(void);
@@ -6609,6 +6643,7 @@ Init_process(void)
     rb_define_module_function(rb_mProcess, "getpgid", proc_getpgid, 1);
     rb_define_module_function(rb_mProcess, "setpgid", proc_setpgid, 2);
 
+    rb_define_module_function(rb_mProcess, "getsid", proc_getsid, -1);
     rb_define_module_function(rb_mProcess, "setsid", proc_setsid, 0);
 
     rb_define_module_function(rb_mProcess, "getpriority", proc_getpriority, 2);
diff --git a/test/ruby/test_process.rb b/test/ruby/test_process.rb
index b549b6f770..c4427be33c 100644
--- a/test/ruby/test_process.rb
+++ b/test/ruby/test_process.rb
@@ -1558,4 +1558,19 @@ class TestProcess < Test::Unit::TestCase
     }
   end if File.executable?("/bin/sh")
 
+  def test_setsid
+    return unless Process.respond_to?(:setsid)
+    return unless Process.respond_to?(:getsid)
+
+    IO.popen(["./ruby-trunk", "-e", <<EOS]) do|io|
+	Marshal.dump(Process.getsid, STDOUT)
+	newsid = Process.setsid
+	Marshal.dump(newsid, STDOUT)
+	STDOUT.flush
+EOS
+
+      assert_equal(Marshal.load(io), Process.getsid)
+      assert_equal(Marshal.load(io), Process.getsid(io.pid))
+    end
+  end
 end