diff --git a/.gitignore b/.gitignore
index c1dff8bfec..dad8be1a48 100644
--- a/.gitignore
+++ b/.gitignore
@@ -172,6 +172,7 @@ cscope.*
 /src/test/test-child
 /src/test/test-memwipe
 /src/test/test-ntor-cl
+/src/test/test-switch-id
 /src/test/test_workqueue
 /src/test/test.exe
 /src/test/test-slow.exe
@@ -179,6 +180,7 @@ cscope.*
 /src/test/test-child.exe
 /src/test/test-ntor-cl.exe
 /src/test/test-memwipe.exe
+/src/test/test-switch-id.exe
 /src/test/test_workqueue.exe
 /src/test/test_zero_length_keys.sh
 /src/test/test_ntor.sh
diff --git a/src/test/include.am b/src/test/include.am
index d0a819fb7f..3fed3b7344 100644
--- a/src/test/include.am
+++ b/src/test/include.am
@@ -4,14 +4,16 @@ export SHELL=@SHELL@
 export abs_top_srcdir=@abs_top_srcdir@
 export builddir=@builddir@
 
-TESTSCRIPTS = src/test/test_zero_length_keys.sh
+TESTSCRIPTS = src/test/test_zero_length_keys.sh \
+	src/test/test_switch_id.sh
 
 if USEPYTHON
 TESTSCRIPTS += src/test/test_ntor.sh src/test/test_bt.sh
 endif
 
 TESTS += src/test/test src/test/test-slow src/test/test-memwipe \
-	src/test/test_workqueue src/test/test_keygen.sh $(TESTSCRIPTS)
+	src/test/test_workqueue src/test/test_keygen.sh \
+	$(TESTSCRIPTS)
 
 # These flavors are run using automake's test-driver and test-network.sh
 TEST_CHUTNEY_FLAVORS = basic-min bridges-min hs-min bridges+hs
@@ -33,7 +35,8 @@ noinst_PROGRAMS+= \
 	src/test/test-slow \
 	src/test/test-memwipe \
 	src/test/test-child \
-	src/test/test_workqueue
+	src/test/test_workqueue \
+	src/test/test-switch-id
 endif
 
 src_test_AM_CPPFLAGS = -DSHARE_DATADIR="\"$(datadir)\"" \
@@ -131,6 +134,14 @@ src_test_test_workqueue_SOURCES = \
 src_test_test_workqueue_CPPFLAGS= $(src_test_AM_CPPFLAGS)
 src_test_test_workqueue_CFLAGS = $(AM_CFLAGS) $(TEST_CFLAGS)
 
+src_test_test_switch_id_SOURCES = \
+	src/test/test_switch_id.c
+src_test_test_switch_id_CPPFLAGS= $(src_test_AM_CPPFLAGS)
+src_test_test_switch_id_CFLAGS = $(AM_CFLAGS) $(TEST_CFLAGS)
+src_test_test_switch_id_LDADD = \
+	src/common/libor-testing.a \
+	@TOR_ZLIB_LIBS@ @TOR_LIB_MATH@
+
 src_test_test_LDFLAGS = @TOR_LDFLAGS_zlib@ @TOR_LDFLAGS_openssl@ \
         @TOR_LDFLAGS_libevent@
 src_test_test_LDADD = src/or/libtor-testing.a src/common/libor-testing.a \
diff --git a/src/test/test_switch_id.c b/src/test/test_switch_id.c
new file mode 100644
index 0000000000..e85025c3b5
--- /dev/null
+++ b/src/test/test_switch_id.c
@@ -0,0 +1,181 @@
+/* Copyright (c) 2015, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+#include "or.h"
+
+#ifdef HAVE_SYS_CAPABILITY_H
+#include <sys/capability.h>
+#endif
+
+#define TEST_BUILT_WITH_CAPS         0
+#define TEST_HAVE_CAPS               1
+#define TEST_ROOT_CAN_BIND_LOW       2
+#define TEST_SETUID                  3
+#define TEST_SETUID_KEEPCAPS         4
+#define TEST_SETUID_STRICT           5
+
+static const char *username;
+
+static const struct {
+  const char *name;
+  int test_id;
+} which_test[] = {
+  { "built-with-caps",    TEST_BUILT_WITH_CAPS },
+  { "have-caps",          TEST_HAVE_CAPS },
+  { "root-bind-low",      TEST_ROOT_CAN_BIND_LOW },
+  { "setuid",             TEST_SETUID },
+  { "setuid-keepcaps",    TEST_SETUID_KEEPCAPS },
+  { "setuid-strict",      TEST_SETUID_STRICT },
+  { NULL, 0 }
+};
+
+/* 0 on no, 1 on yes, -1 on failure. */
+static int
+check_can_bind_low_ports(void)
+{
+  int port;
+  struct sockaddr_in sin;
+  memset(&sin, 0, sizeof(sin));
+  sin.sin_family = AF_INET;
+
+  for (port = 600; port < 1024; ++port) {
+    sin.sin_port = htons(port);
+    tor_socket_t fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
+    if (! SOCKET_OK(fd)) {
+      perror("socket");
+      return -1;
+    }
+
+    int one = 1;
+    if (setsockopt(fd, SOL_SOCKET,SO_REUSEADDR, &one, sizeof(one))) {
+      perror("setsockopt");
+      tor_close_socket_simple(fd);
+      return -1;
+    }
+
+    int res = bind(fd, (struct sockaddr *)&sin, sizeof(sin));
+    tor_close_socket_simple(fd);
+
+    if (res == 0) {
+      /* bind was successful */
+      return 1;
+    } else if (errno == EACCES || errno == EPERM) {
+      /* Got a permission-denied error. */
+      return 0;
+    } else if (errno == EADDRINUSE) {
+      /* Huh; somebody is using that port. */
+    } else {
+      perror("bind");
+    }
+  }
+
+  return -1;
+}
+
+int
+main(int argc, char **argv)
+{
+  const char *testname;
+  if (argc != 3) {
+    fprintf(stderr, "I want 2 arguments: a username and a command.\n");
+    return 1;
+  }
+  if (getuid() != 0) {
+    fprintf(stderr, "This test only works when it's run as root.\n");
+    return 1;
+  }
+  username = argv[1];
+  testname = argv[2];
+  int test_id = -1;
+  int i;
+  for (i = 0; which_test[i].name; ++i) {
+    if (!strcmp(which_test[i].name, testname)) {
+      test_id = which_test[i].test_id;
+      break;
+    }
+  }
+  if (test_id == -1) {
+    fprintf(stderr, "Unrecognized test '%s'\n", testname);
+    return 1;
+  }
+
+#ifdef HAVE_LINUX_CAPABILITIES
+  const int have_cap_support = 1;
+#else
+  const int have_cap_support = 0;
+#endif
+
+  int okay;
+
+  init_logging(1);
+  log_severity_list_t sev;
+  memset(&sev, 0, sizeof(sev));
+  set_log_severity_config(LOG_WARN, LOG_ERR, &sev);
+  add_stream_log(&sev, "", fileno(stderr));
+
+  switch (test_id)
+    {
+    case TEST_BUILT_WITH_CAPS:
+      /* Succeed if we were built with capability support. */
+      okay = have_cap_support;
+      break;
+    case TEST_HAVE_CAPS:
+      /* Succeed if "capabilities work" == "we were built with capability
+       * support." */
+      okay = have_cap_support == have_capability_support();
+      break;
+    case TEST_ROOT_CAN_BIND_LOW:
+      /* Succeed if root can bind low ports. */
+      okay = check_can_bind_low_ports() == 1;
+      break;
+    case TEST_SETUID:
+      /* Succeed if we can do a setuid with no capability retention, and doing
+       * so makes us lose the ability to bind low ports */
+    case TEST_SETUID_KEEPCAPS:
+      /* Succeed if we can do a setuid with capability retention, and doing so
+       * does not make us lose the ability to bind low ports */
+    {
+      int keepcaps = (test_id == TEST_SETUID_KEEPCAPS);
+      okay = switch_id(username, keepcaps ? SWITCH_ID_KEEP_BINDLOW : 0) == 0;
+      if (okay) {
+        okay = check_can_bind_low_ports() == keepcaps;
+      }
+      break;
+    }
+    case TEST_SETUID_STRICT:
+      /* Succeed if, after a setuid, we cannot setuid back, and we cannot
+       * re-grab any capabilities. */
+      okay = switch_id(username, SWITCH_ID_KEEP_BINDLOW) == 0;
+      if (okay) {
+        /* We'd better not be able to setuid back! */
+        if (setuid(0) == 0 || errno != EPERM) {
+          okay = 0;
+        }
+      }
+#ifdef HAVE_LINUX_CAPABILITIES
+      if (okay) {
+        cap_t caps = cap_get_proc();
+        const cap_value_t caplist[] = {
+          CAP_SETUID,
+        };
+        cap_set_flag(caps, CAP_PERMITTED, 1, caplist, CAP_SET);
+        if (cap_set_proc(caps) == 0 || errno != EPERM) {
+          okay = 0;
+        }
+        cap_free(caps);
+      }
+#endif
+      break;
+    default:
+      fprintf(stderr, "Unsupported test '%s'\n", testname);
+      okay = 0;
+      break;
+    }
+
+  if (!okay) {
+    fprintf(stderr, "Test %s failed!\n", testname);
+  }
+
+  return (okay ? 0 : 1);
+}
+
diff --git a/src/test/test_switch_id.sh b/src/test/test_switch_id.sh
new file mode 100755
index 0000000000..1b4e0998b5
--- /dev/null
+++ b/src/test/test_switch_id.sh
@@ -0,0 +1,25 @@
+#!/bin/sh
+
+if test "`id -u`" != '0'; then
+    echo "This test only works when run as root. Skipping." >&2
+    exit 77
+fi
+
+if test "`id -u nobody`" = ""; then
+    echo "This test requires that your system have a 'nobody' user. Sorry." >&2
+    exit 1
+fi
+
+"${builddir:-.}/src/test/test-switch-id" nobody setuid          || exit 1
+"${builddir:-.}/src/test/test-switch-id" nobody root-bind-low   || exit 1
+"${builddir:-.}/src/test/test-switch-id" nobody setuid-strict   || exit 1
+"${builddir:-.}/src/test/test-switch-id" nobody built-with-caps || exit 0
+# ... Go beyond this point only if we were built with capability support.
+
+"${builddir:-.}/src/test/test-switch-id" nobody have-caps       || exit 1
+"${builddir:-.}/src/test/test-switch-id" nobody setuid-keepcaps || exit 1
+
+
+echo "All okay"
+
+exit 0