diff --git a/man/sd_get_seats.xml b/man/sd_get_seats.xml
index 37eb3fc894..c053144483 100644
--- a/man/sd_get_seats.xml
+++ b/man/sd_get_seats.xml
@@ -81,8 +81,10 @@
     <title>Description</title>
 
     <para><function>sd_get_seats()</function> may be used to determine
-    all currently available local seats. Returns a
-    <constant>NULL</constant> terminated array of seat identifiers.
+    all currently available local seats. Returns the number of seat
+    identifiers and if the input pointer is non-NULL, a
+    <constant>NULL</constant>-terminated array of seat identifiers
+    is stored at the address.
     The returned array and all strings it references need to be freed
     with the libc
     <citerefentry project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
@@ -123,13 +125,6 @@
 
     <variablelist>
 
-      <varlistentry>
-        <term><constant>-EINVAL</constant></term>
-
-        <listitem><para>An input parameter was invalid (out of range,
-        or NULL, where that is not accepted).</para></listitem>
-      </varlistentry>
-
       <varlistentry>
         <term><constant>-ENOMEM</constant></term>
 
diff --git a/man/sd_pid_get_session.xml b/man/sd_pid_get_session.xml
index 0c135ba871..14ebd53e36 100644
--- a/man/sd_pid_get_session.xml
+++ b/man/sd_pid_get_session.xml
@@ -285,7 +285,7 @@
       </varlistentry>
 
       <varlistentry>
-        <term><constant>-BADF</constant></term>
+        <term><constant>-EBADF</constant></term>
 
         <listitem><para>The specified socket file descriptor was
         invalid.</para></listitem>
diff --git a/src/libsystemd/sd-bus/test-bus-vtable.c b/src/libsystemd/sd-bus/test-bus-vtable.c
index 31c35e8540..fd9ad81217 100644
--- a/src/libsystemd/sd-bus/test-bus-vtable.c
+++ b/src/libsystemd/sd-bus/test-bus-vtable.c
@@ -4,6 +4,7 @@
 /* We use system assert.h here, because we don't want to keep macro.h and log.h C++ compatible */
 #undef NDEBUG
 #include <assert.h>
+#include <errno.h>
 
 #include "sd-bus-vtable.h"
 
@@ -58,6 +59,7 @@ static const sd_bus_vtable vtable[] = {
 static void test_vtable(void) {
         sd_bus *bus = NULL;
         struct context c = {};
+        int r;
 
         assert(sd_bus_new(&bus) >= 0);
 
@@ -65,7 +67,9 @@ static void test_vtable(void) {
         assert(sd_bus_add_object_vtable(bus, NULL, "/foo", "org.freedesktop.systemd.testVtable2", vtable, &c) >= 0);
 
         assert(sd_bus_set_address(bus, DEFAULT_BUS_PATH) >= 0);
-        assert(sd_bus_start(bus) >= 0);
+        r = sd_bus_start(bus);
+        assert(r == 0 ||     /* success */
+               r == -ENOENT  /* dbus is inactive */ );
 
         sd_bus_unref(bus);
 }
diff --git a/src/libsystemd/sd-login/sd-login.c b/src/libsystemd/sd-login/sd-login.c
index 25dff7738f..b75acef82c 100644
--- a/src/libsystemd/sd-login/sd-login.c
+++ b/src/libsystemd/sd-login/sd-login.c
@@ -62,7 +62,7 @@ _public_ int sd_pid_get_session(pid_t pid, char **session) {
         assert_return(session, -EINVAL);
 
         r = cg_pid_get_session(pid, session);
-        return r == -ENXIO ? -ENODATA : r;
+        return IN_SET(r, -ENXIO, -ENOMEDIUM) ? -ENODATA : r;
 }
 
 _public_ int sd_pid_get_unit(pid_t pid, char **unit) {
@@ -72,7 +72,7 @@ _public_ int sd_pid_get_unit(pid_t pid, char **unit) {
         assert_return(unit, -EINVAL);
 
         r = cg_pid_get_unit(pid, unit);
-        return r == -ENXIO ? -ENODATA : r;
+        return IN_SET(r, -ENXIO, -ENOMEDIUM) ? -ENODATA : r;
 }
 
 _public_ int sd_pid_get_user_unit(pid_t pid, char **unit) {
@@ -82,39 +82,47 @@ _public_ int sd_pid_get_user_unit(pid_t pid, char **unit) {
         assert_return(unit, -EINVAL);
 
         r = cg_pid_get_user_unit(pid, unit);
-        return r == -ENXIO ? -ENODATA : r;
+        return IN_SET(r, -ENXIO, -ENOMEDIUM) ? -ENODATA : r;
 }
 
 _public_ int sd_pid_get_machine_name(pid_t pid, char **name) {
+        int r;
 
         assert_return(pid >= 0, -EINVAL);
         assert_return(name, -EINVAL);
 
-        return cg_pid_get_machine_name(pid, name);
+        r = cg_pid_get_machine_name(pid, name);
+        return IN_SET(r, -ENXIO, -ENOMEDIUM) ? -ENODATA : r;
 }
 
 _public_ int sd_pid_get_slice(pid_t pid, char **slice) {
+        int r;
 
         assert_return(pid >= 0, -EINVAL);
         assert_return(slice, -EINVAL);
 
-        return cg_pid_get_slice(pid, slice);
+        r = cg_pid_get_slice(pid, slice);
+        return IN_SET(r, -ENXIO, -ENOMEDIUM) ? -ENODATA : r;
 }
 
 _public_ int sd_pid_get_user_slice(pid_t pid, char **slice) {
+        int r;
 
         assert_return(pid >= 0, -EINVAL);
         assert_return(slice, -EINVAL);
 
-        return cg_pid_get_user_slice(pid, slice);
+        r = cg_pid_get_user_slice(pid, slice);
+        return IN_SET(r, -ENXIO, -ENOMEDIUM) ? -ENODATA : r;
 }
 
 _public_ int sd_pid_get_owner_uid(pid_t pid, uid_t *uid) {
+        int r;
 
         assert_return(pid >= 0, -EINVAL);
         assert_return(uid, -EINVAL);
 
-        return cg_pid_get_owner_uid(pid, uid);
+        r = cg_pid_get_owner_uid(pid, uid);
+        return IN_SET(r, -ENXIO, -ENOMEDIUM) ? -ENODATA : r;
 }
 
 _public_ int sd_pid_get_cgroup(pid_t pid, char **cgroup) {
@@ -790,11 +798,27 @@ _public_ int sd_seat_can_graphical(const char *seat) {
 }
 
 _public_ int sd_get_seats(char ***seats) {
-        return get_files_in_directory("/run/systemd/seats/", seats);
+        int r;
+
+        r = get_files_in_directory("/run/systemd/seats/", seats);
+        if (r == -ENOENT) {
+                if (seats)
+                        *seats = NULL;
+                return 0;
+        }
+        return r;
 }
 
 _public_ int sd_get_sessions(char ***sessions) {
-        return get_files_in_directory("/run/systemd/sessions/", sessions);
+        int r;
+
+        r = get_files_in_directory("/run/systemd/sessions/", sessions);
+        if (r == -ENOENT) {
+                if (sessions)
+                        *sessions = NULL;
+                return 0;
+        }
+        return r;
 }
 
 _public_ int sd_get_uids(uid_t **users) {
@@ -805,8 +829,14 @@ _public_ int sd_get_uids(uid_t **users) {
         _cleanup_free_ uid_t *l = NULL;
 
         d = opendir("/run/systemd/users/");
-        if (!d)
+        if (!d) {
+                if (errno == ENOENT) {
+                        if (users)
+                                *users = NULL;
+                        return 0;
+                }
                 return -errno;
+        }
 
         FOREACH_DIRENT_ALL(de, d, return -errno) {
                 int k;
@@ -848,14 +878,13 @@ _public_ int sd_get_uids(uid_t **users) {
 }
 
 _public_ int sd_get_machine_names(char ***machines) {
-        char **l = NULL, **a, **b;
+        char **l, **a, **b;
         int r;
 
-        assert_return(machines, -EINVAL);
-
         r = get_files_in_directory("/run/systemd/machines/", &l);
         if (r == -ENOENT) {
-                *machines = NULL;
+                if (machines)
+                        *machines = NULL;
                 return 0;
         }
         if (r < 0)
@@ -865,7 +894,7 @@ _public_ int sd_get_machine_names(char ***machines) {
                 r = 0;
 
                 /* Filter out the unit: symlinks */
-                for (a = l, b = l; *a; a++) {
+                for (a = b = l; *a; a++) {
                         if (startswith(*a, "unit:") || !machine_name_is_valid(*a))
                                 free(*a);
                         else {
@@ -878,7 +907,8 @@ _public_ int sd_get_machine_names(char ***machines) {
                 *b = NULL;
         }
 
-        *machines = l;
+        if (machines)
+                *machines = l;
         return r;
 }
 
diff --git a/src/libsystemd/sd-login/test-login.c b/src/libsystemd/sd-login/test-login.c
index 6a51ae6a91..b618b79b28 100644
--- a/src/libsystemd/sd-login/test-login.c
+++ b/src/libsystemd/sd-login/test-login.c
@@ -61,14 +61,15 @@ static void test_login(void) {
 
         r = sd_pid_get_unit(0, &unit);
         assert_se(r >= 0 || r == -ENODATA);
-        log_info("sd_pid_get_unit(0, …) → \"%s\"", unit);
+        log_info("sd_pid_get_unit(0, …) → \"%s\"", strna(unit));
 
         r = sd_pid_get_user_unit(0, &user_unit);
         assert_se(r >= 0 || r == -ENODATA);
-        log_info("sd_pid_get_user_unit(0, …) → \"%s\"", user_unit);
+        log_info("sd_pid_get_user_unit(0, …) → \"%s\"", strna(user_unit));
 
-        assert_se(sd_pid_get_slice(0, &slice) >= 0);
-        log_info("sd_pid_get_slice(0, …) → \"%s\"", slice);
+        r = sd_pid_get_slice(0, &slice);
+        assert_se(r >= 0 || r == -ENODATA);
+        log_info("sd_pid_get_slice(0, …) → \"%s\"", strna(slice));
 
         r = sd_pid_get_session(0, &session);
         if (r < 0) {
@@ -248,8 +249,9 @@ static void test_login(void) {
                 assert_se(r >= 0);
                 assert_se(r == (int) strv_length(machines));
                 assert_se(buf = strv_join(machines, " "));
-
                 log_info("sd_get_machines(…) → [%i] \"%s\"", r, buf);
+
+                assert_se(sd_get_machine_names(NULL) == r);
         }
 }