diff --git a/ChangeLog b/ChangeLog
index cbada31fcd..a54158c59d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Feb  8 18:46:15 2009  Tanaka Akira  <akr@fsij.org>
+
+	* ext/socket/ancdata.c (anc_inspect_passcred_credentials): new
+	  function to show SCM_CREDENTIALS on GNU/Linux.
+
 Sun Feb  8 18:34:43 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* io.c (rb_io_s_binread): ensures file path.  [ruby-dev:37940]
diff --git a/ext/socket/ancdata.c b/ext/socket/ancdata.c
index d9e54f4725..012f8d34b7 100644
--- a/ext/socket/ancdata.c
+++ b/ext/socket/ancdata.c
@@ -376,6 +376,23 @@ anc_inspect_socket_rights(int level, int type, VALUE data, VALUE ret)
 }
 #endif
 
+#if defined(SCM_CREDENTIALS) /* GNU/Linux */
+static int
+anc_inspect_passcred_credentials(int level, int type, VALUE data, VALUE ret)
+{
+    if (level == SOL_SOCKET && type == SCM_CREDENTIALS &&
+        RSTRING_LEN(data) == sizeof(struct ucred)) {
+        struct ucred cred;
+        memcpy(&cred, RSTRING_PTR(data), sizeof(struct ucred));
+        rb_str_catf(ret, " pid=%u uid=%u gid=%u", cred.pid, cred.uid, cred.gid);
+        return 0;
+    }
+    else {
+        return -1;
+    }
+}
+#endif
+
 #if defined(IPPROTO_IP) && defined(IP_RECVDSTADDR) /* 4.4BSD */
 static int
 anc_inspect_ip_recvdstaddr(int level, int type, VALUE data, VALUE ret)
@@ -496,6 +513,9 @@ ancillary_inspect(VALUE self)
         switch (type) {
 #        if defined(SCM_RIGHTS) /* 4.4BSD */
           case SCM_RIGHTS: if (anc_inspect_socket_rights(level, type, data, ret) == -1) goto dump; break;
+#        endif
+#        if defined(SCM_CREDENTIALS) /* GNU/Linux */
+          case SCM_CREDENTIALS: if (anc_inspect_passcred_credentials(level, type, data, ret) == -1) goto dump; break;
 #        endif
           default: goto dump;
         }