core: add transient units

Transient units can be created via the bus API. They are configured via
the method call parameters rather than on-disk files. They are subject
to normal GC. Transient units currently may only be created for
services (however, we will extend this), and currently only ExecStart=
and the cgroup parameters can be configured (also to be extended).

Transient units require a unique name, that previously had no
configuration file on disk.

A tool systemd-run is added that makes use of this functionality to run
arbitrary command lines as transient services:

$ systemd-run /bin/ping www.heise.de

Will cause systemd to create a new transient service and run ping in it.

14 files changed, 382 insertions, 51 deletions

diff --git a/src/core/dbus-cgroup.c b/src/core/dbus-cgroup.c
index cf05f04ea1..d1d35633c1 100644
--- a/src/core/dbus-cgroup.c
+++ b/src/core/dbus-cgroup.c
@@ -323,8 +323,6 @@ int bus_cgroup_set_property(
                                 return -EINVAL;
                         }
 
-                        n++;
-
                         if (mode != UNIT_CHECK) {
                                 a = new0(CGroupDeviceAllow, 1);
                                 if (!a)
@@ -343,6 +341,7 @@ int bus_cgroup_set_property(
                                 LIST_PREPEND(CGroupDeviceAllow, device_allow, c->device_allow, a);
                         }
 
+                        n++;
                         dbus_message_iter_next(&sub);
                 }
 
diff --git a/src/core/dbus-manager.c b/src/core/dbus-manager.c
index c512265903..fe2f749803 100644
--- a/src/core/dbus-manager.c
+++ b/src/core/dbus-manager.c
@@ -239,6 +239,13 @@
         "   <arg name=\"name\" type=\"s\" direction=\"out\"/>\n"        \
         "   <arg name=\"runtime\" type=\"b\" direction=\"in\"/>\n"      \
         "   <arg name=\"properties\" type=\"a(sv)\" direction=\"in\"/>\n" \
+        "  </method>\n"                                                 \
+        "  <method name=\"StartTransientUnit\">\n"                      \
+        "   <arg name=\"name\" type=\"s\" direction=\"in\"/>\n"         \
+        "   <arg name=\"mode\" type=\"s\" direction=\"in\"/>\n"         \
+        "   <arg name=\"properties\" type=\"a(sv)\" direction=\"in\"/>\n" \
+        "   <arg name=\"aux\" type=\"a(sa(sv))\" direction=\"in\"/>\n"  \
+        "   <arg name=\"job\" type=\"o\" direction=\"out\"/>\n"         \
         "  </method>\n"
 
 #define BUS_MANAGER_INTERFACE_SIGNALS                                   \
@@ -1758,7 +1765,7 @@ static DBusHandlerResult bus_manager_message_handler(DBusConnection *connection,
 
                 SELINUX_UNIT_ACCESS_CHECK(u, connection, message, "start");
 
-                r = bus_unit_set_properties(u, &iter, runtime ? UNIT_RUNTIME : UNIT_PERSISTENT, &error);
+                r = bus_unit_set_properties(u, &iter, runtime ? UNIT_RUNTIME : UNIT_PERSISTENT, true, &error);
                 if (r < 0)
                         return bus_send_error_reply(connection, message, &error, r);
 
@@ -1766,6 +1773,66 @@ static DBusHandlerResult bus_manager_message_handler(DBusConnection *connection,
                 if (!reply)
                         goto oom;
 
+        } else if (dbus_message_is_method_call(message, "org.freedesktop.systemd1.Manager", "StartTransientUnit")) {
+                const char *name, *smode;
+                DBusMessageIter iter;
+                JobMode mode;
+                UnitType t;
+                Unit *u;
+
+                if (!dbus_message_iter_init(message, &iter))
+                        goto oom;
+
+                if (bus_iter_get_basic_and_next(&iter, DBUS_TYPE_STRING, &name, true) < 0 ||
+                    bus_iter_get_basic_and_next(&iter, DBUS_TYPE_STRING, &smode, true) < 0)
+                        return bus_send_error_reply(connection, message, NULL, -EINVAL);
+
+                t = unit_name_to_type(name);
+                if (t < 0)
+                        return bus_send_error_reply(connection, message, NULL, -EINVAL);
+                if (!unit_vtable[t]->can_transient) {
+                        dbus_set_error(&error, DBUS_ERROR_INVALID_ARGS, "Unit type %s does not support transient units.", unit_type_to_string(t));
+                        return bus_send_error_reply(connection, message, &error, -EINVAL);
+                }
+
+                mode = job_mode_from_string(smode);
+                if (mode < 0) {
+                        dbus_set_error(&error, BUS_ERROR_INVALID_JOB_MODE, "Job mode %s is invalid.", smode);
+                        return bus_send_error_reply(connection, message, &error, -EINVAL);
+                }
+
+                r = manager_load_unit(m, name, NULL, NULL, &u);
+                if (r < 0)
+                        return bus_send_error_reply(connection, message, &error, r);
+
+                SELINUX_UNIT_ACCESS_CHECK(u, connection, message, "start");
+
+                if (u->load_state != UNIT_NOT_FOUND || set_size(u->dependencies[UNIT_REFERENCED_BY]) > 0) {
+                        dbus_set_error(&error, BUS_ERROR_UNIT_EXISTS, "Unit %s already exists.", name);
+                        return bus_send_error_reply(connection, message, &error, -EEXIST);
+                }
+
+                /* OK, the unit failed to load and is unreferenced,
+                 * now let's fill in the transient data instead */
+                r = unit_make_transient(u);
+                if (r < 0)
+                        return bus_send_error_reply(connection, message, &error, r);
+
+                /* Set our properties */
+                r = bus_unit_set_properties(u, &iter, UNIT_RUNTIME, false, &error);
+                if (r < 0)
+                        return bus_send_error_reply(connection, message, &error, r);
+
+                /* And load this stub fully */
+                r = unit_load(u);
+                if (r < 0)
+                        return bus_send_error_reply(connection, message, &error, r);
+
+                manager_dispatch_load_queue(m);
+
+                /* Finally, start it */
+                return bus_unit_queue_job(connection, message, u, JOB_START, mode, false);
+
         } else {
                 const BusBoundProperties bps[] = {
                         { "org.freedesktop.systemd1.Manager", bus_systemd_properties, systemd_property_string },
diff --git a/src/core/dbus-service.c b/src/core/dbus-service.c
index 867ef7e54c..c2031c3bf1 100644
--- a/src/core/dbus-service.c
+++ b/src/core/dbus-service.c
@@ -21,6 +21,8 @@
 
 #include <errno.h>
 
+#include "strv.h"
+#include "path-util.h"
 #include "dbus-unit.h"
 #include "dbus-execute.h"
 #include "dbus-kill.h"
@@ -162,6 +164,124 @@ DBusHandlerResult bus_service_message_handler(Unit *u, DBusConnection *connectio
         return bus_default_message_handler(connection, message, INTROSPECTION, INTERFACES_LIST, bps);
 }
 
+static int bus_service_set_transient_properties(
+                Service *s,
+                const char *name,
+                DBusMessageIter *i,
+                UnitSetPropertiesMode mode,
+                DBusError *error) {
+
+        int r;
+
+        assert(name);
+        assert(s);
+        assert(i);
+
+        if (streq(name, "ExecStart")) {
+                DBusMessageIter sub;
+                unsigned n = 0;
+
+                if (dbus_message_iter_get_arg_type(i) != DBUS_TYPE_ARRAY ||
+                    dbus_message_iter_get_element_type(i) != DBUS_TYPE_STRUCT)
+                        return -EINVAL;
+
+                dbus_message_iter_recurse(i, &sub);
+                while (dbus_message_iter_get_arg_type(&sub) == DBUS_TYPE_STRUCT) {
+                        _cleanup_strv_free_ char **argv = NULL;
+                        DBusMessageIter sub2;
+                        dbus_bool_t ignore;
+                        const char *path;
+
+                        dbus_message_iter_recurse(&sub, &sub2);
+
+                        if (bus_iter_get_basic_and_next(&sub2, DBUS_TYPE_STRING, &path, true) < 0)
+                                return -EINVAL;
+
+                        if (!path_is_absolute(path)) {
+                                dbus_set_error(error, DBUS_ERROR_INVALID_ARGS, "Path %s is not absolute.", path);
+                                return -EINVAL;
+                        }
+
+                        r = bus_parse_strv_iter(&sub2, &argv);
+                        if (r < 0)
+                                return r;
+
+                        dbus_message_iter_next(&sub2);
+
+                        if (bus_iter_get_basic_and_next(&sub2, DBUS_TYPE_BOOLEAN, &ignore, false) < 0)
+                                return -EINVAL;
+
+                        if (mode != UNIT_CHECK) {
+                                ExecCommand *c;
+
+                                c = new0(ExecCommand, 1);
+                                if (!c)
+                                        return -ENOMEM;
+
+                                c->path = strdup(path);
+                                if (!c->path) {
+                                        free(c);
+                                        return -ENOMEM;
+                                }
+
+                                c->argv = argv;
+                                argv = NULL;
+
+                                c->ignore = ignore;
+
+                                path_kill_slashes(c->path);
+                                exec_command_append_list(&s->exec_command[SERVICE_EXEC_START], c);
+                        }
+
+                        n++;
+                        dbus_message_iter_next(&sub);
+                }
+
+                if (mode != UNIT_CHECK) {
+                        _cleanup_free_ char *buf = NULL;
+                        _cleanup_fclose_ FILE *f = NULL;
+                        ExecCommand *c;
+                        size_t size = 0;
+
+                        if (n == 0) {
+                                exec_command_free_list(s->exec_command[SERVICE_EXEC_START]);
+                                s->exec_command[SERVICE_EXEC_START] = NULL;
+                        }
+
+                        f = open_memstream(&buf, &size);
+                        if (!f)
+                                return -ENOMEM;
+
+                        fputs("ExecStart=\n", f);
+
+                        LIST_FOREACH(command, c, s->exec_command[SERVICE_EXEC_START]) {
+                                char **a;
+                                fputs("ExecStart=", f);
+
+                                if (c->ignore)
+                                        fputc('-', f);
+
+                                fputc('@', f);
+                                fputs(c->path, f);
+
+                                STRV_FOREACH(a, c->argv) {
+                                        fputc(' ', f);
+                                        fputs(*a, f);
+                                }
+
+                                fputc('\n', f);
+                        }
+
+                        fflush(f);
+                        unit_write_drop_in_private_section(UNIT(s), mode, "exec-start", buf);
+                }
+
+                return 1;
+        }
+
+        return 0;
+}
+
 int bus_service_set_property(
                 Unit *u,
                 const char *name,
@@ -180,6 +300,14 @@ int bus_service_set_property(
         if (r != 0)
                 return r;
 
+        if (u->transient && u->load_state == UNIT_STUB) {
+                /* This is a transient unit, let's load a little more */
+
+                r = bus_service_set_transient_properties(s, name, i, mode, error);
+                if (r != 0)
+                        return r;
+        }
+
         return 0;
 }
 
diff --git a/src/core/dbus-unit.c b/src/core/dbus-unit.c
index b3724b679b..f518505750 100644
--- a/src/core/dbus-unit.c
+++ b/src/core/dbus-unit.c
@@ -415,7 +415,7 @@ static DBusHandlerResult bus_unit_message_dispatch(Unit *u, DBusConnection *conn
 
                 SELINUX_UNIT_ACCESS_CHECK(u, connection, message, "start");
 
-                r = bus_unit_set_properties(u, &iter, runtime ? UNIT_RUNTIME : UNIT_PERSISTENT, &error);
+                r = bus_unit_set_properties(u, &iter, runtime ? UNIT_RUNTIME : UNIT_PERSISTENT, true, &error);
                 if (r < 0)
                         return bus_send_error_reply(connection, message, &error, r);
 
@@ -716,7 +716,7 @@ DBusHandlerResult bus_unit_queue_job(
                                   (type == JOB_START || type == JOB_RESTART || type == JOB_TRY_RESTART) ? "start" :
                                   type == JOB_STOP ? "stop" : "reload");
 
-        if (type == JOB_STOP && u->load_state == UNIT_ERROR && unit_active_state(u) == UNIT_INACTIVE) {
+        if (type == JOB_STOP && (u->load_state == UNIT_NOT_FOUND || u->load_state == UNIT_ERROR) && unit_active_state(u) == UNIT_INACTIVE) {
                 dbus_set_error(&error, BUS_ERROR_NO_SUCH_UNIT, "Unit %s not loaded.", u->id);
                 return bus_send_error_reply(connection, message, &error, -EPERM);
         }
@@ -764,7 +764,13 @@ oom:
         return DBUS_HANDLER_RESULT_NEED_MEMORY;
 }
 
-int bus_unit_set_properties(Unit *u, DBusMessageIter *iter, UnitSetPropertiesMode mode, DBusError *error) {
+int bus_unit_set_properties(
+                Unit *u,
+                DBusMessageIter *iter,
+                UnitSetPropertiesMode mode,
+                bool commit,
+                DBusError *error) {
+
         bool for_real = false;
         DBusMessageIter sub;
         unsigned n = 0;
@@ -773,6 +779,9 @@ int bus_unit_set_properties(Unit *u, DBusMessageIter *iter, UnitSetPropertiesMod
         assert(u);
         assert(iter);
 
+        if (u->transient)
+                mode &= UNIT_RUNTIME;
+
         /* We iterate through the array twice. First run we just check
          * if all passed data is valid, second run actually applies
          * it. This is to implement transaction-like behaviour without
@@ -826,7 +835,7 @@ int bus_unit_set_properties(Unit *u, DBusMessageIter *iter, UnitSetPropertiesMod
                 n += for_real;
         }
 
-        if (n > 0 && UNIT_VTABLE(u)->bus_commit_properties)
+        if (commit && n > 0 && UNIT_VTABLE(u)->bus_commit_properties)
                 UNIT_VTABLE(u)->bus_commit_properties(u);
 
         return n;
@@ -896,5 +905,6 @@ const BusProperty bus_unit_properties[] = {
         { "ConditionResult",      bus_property_append_bool,           "b", offsetof(Unit, condition_result)                   },
         { "LoadError",            bus_unit_append_load_error,      "(ss)", 0 },
         { "ControlGroup",         bus_property_append_string,         "s", offsetof(Unit, cgroup_path),                                true },
+        { "Transient",            bus_property_append_bool,           "b", offsetof(Unit, transient)                          },
         { NULL, }
 };
diff --git a/src/core/dbus-unit.h b/src/core/dbus-unit.h
index 1b42757b47..18f7c4f088 100644
--- a/src/core/dbus-unit.h
+++ b/src/core/dbus-unit.h
@@ -128,6 +128,7 @@
         "  <property name=\"ConditionResult\" type=\"b\" access=\"read\"/>\n" \
         "  <property name=\"LoadError\" type=\"(ss)\" access=\"read\"/>\n" \
         "  <property name=\"ControlGroup\" type=\"s\" access=\"read\"/>\n" \
+        "  <property name=\"Transient\" type=\"b\" access=\"read\"/>\n" \
         " </interface>\n"
 
 #define BUS_UNIT_INTERFACES_LIST                \
@@ -141,7 +142,7 @@ void bus_unit_send_removed_signal(Unit *u);
 
 DBusHandlerResult bus_unit_queue_job(DBusConnection *connection, DBusMessage *message, Unit *u, JobType type, JobMode mode, bool reload_if_possible);
 
-int bus_unit_set_properties(Unit *u, DBusMessageIter *i, UnitSetPropertiesMode mode, DBusError *error);
+int bus_unit_set_properties(Unit *u, DBusMessageIter *i, UnitSetPropertiesMode mode, bool commit, DBusError *error);
 
 extern const DBusObjectPathVTable bus_unit_vtable;
 
diff --git a/src/core/job.c b/src/core/job.c
index d304a16d06..85f77e8f0d 100644
--- a/src/core/job.c
+++ b/src/core/job.c
@@ -1088,10 +1088,13 @@ void job_shutdown_magic(Job *j) {
          * asynchronous sync() would cause their exit to be
          * delayed. */
 
-        if (!unit_has_name(j->unit, SPECIAL_SHUTDOWN_TARGET))
+        if (j->type != JOB_START)
                 return;
 
-        if (j->type != JOB_START)
+        if (j->unit->manager->running_as != SYSTEMD_SYSTEM)
+                return;
+
+        if (!unit_has_name(j->unit, SPECIAL_SHUTDOWN_TARGET))
                 return;
 
         if (detect_container(NULL) > 0)
diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c
index 57c8156fdd..2b10d72ab3 100644
--- a/src/core/load-fragment.c
+++ b/src/core/load-fragment.c
@@ -2439,14 +2439,14 @@ static int load_from_path(Unit *u, const char *path) {
         if (null_or_empty(&st))
                 u->load_state = UNIT_MASKED;
         else {
+                u->load_state = UNIT_LOADED;
+
                 /* Now, parse the file contents */
                 r = config_parse(u->id, filename, f, UNIT_VTABLE(u)->sections,
                                  config_item_perf_lookup,
                                  (void*) load_fragment_gperf_lookup, false, true, u);
                 if (r < 0)
                         goto finish;
-
-                u->load_state = UNIT_LOADED;
         }
 
         free(u->fragment_path);
diff --git a/src/core/main.c b/src/core/main.c
index 3c6fccf527..102cc3b315 100644
--- a/src/core/main.c
+++ b/src/core/main.c
@@ -1666,7 +1666,7 @@ int main(int argc, char *argv[]) {
                 if (r < 0) {
                         log_error("Failed to load default target: %s", bus_error(&error, r));
                         dbus_error_free(&error);
-                } else if (target->load_state == UNIT_ERROR)
+                } else if (target->load_state == UNIT_ERROR || target->load_state == UNIT_NOT_FOUND)
                         log_error("Failed to load default target: %s", strerror(-target->load_error));
                 else if (target->load_state == UNIT_MASKED)
                         log_error("Default target masked.");
@@ -1679,7 +1679,7 @@ int main(int argc, char *argv[]) {
                                 log_error("Failed to load rescue target: %s", bus_error(&error, r));
                                 dbus_error_free(&error);
                                 goto finish;
-                        } else if (target->load_state == UNIT_ERROR) {
+                        } else if (target->load_state == UNIT_ERROR || target->load_state == UNIT_ERROR) {
                                 log_error("Failed to load rescue target: %s", strerror(-target->load_error));
                                 goto finish;
                         } else if (target->load_state == UNIT_MASKED) {
diff --git a/src/core/manager.c b/src/core/manager.c
index 6ba51a4116..42c9bcd48c 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -993,7 +993,13 @@ unsigned manager_dispatch_load_queue(Manager *m) {
         return n;
 }
 
-int manager_load_unit_prepare(Manager *m, const char *name, const char *path, DBusError *e, Unit **_ret) {
+int manager_load_unit_prepare(
+                Manager *m,
+                const char *name,
+                const char *path,
+                DBusError *e,
+                Unit **_ret) {
+
         Unit *ret;
         UnitType t;
         int r;
@@ -1053,7 +1059,13 @@ int manager_load_unit_prepare(Manager *m, const char *name, const char *path, DB
         return 0;
 }
 
-int manager_load_unit(Manager *m, const char *name, const char *path, DBusError *e, Unit **_ret) {
+int manager_load_unit(
+                Manager *m,
+                const char *name,
+                const char *path,
+                DBusError *e,
+                Unit **_ret) {
+
         int r;
 
         assert(m);
diff --git a/src/core/mount.c b/src/core/mount.c
index c1af903b12..3cc3e65b23 100644
--- a/src/core/mount.c
+++ b/src/core/mount.c
@@ -1562,7 +1562,7 @@ static int mount_add_one(
                         }
                 }
 
-                if (u->load_state == UNIT_ERROR) {
+                if (u->load_state == UNIT_NOT_FOUND) {
                         u->load_state = UNIT_LOADED;
                         u->load_error = 0;
 
diff --git a/src/core/service.c b/src/core/service.c
index 1dcd5cf443..6f18cbf759 100644
--- a/src/core/service.c
+++ b/src/core/service.c
@@ -983,7 +983,7 @@ static int service_load_sysv_name(Service *s, const char *name) {
         assert(s);
         assert(name);
 
-	/* For SysV services we strip the *.sh suffixes. */
+        /* For SysV services we strip the *.sh suffixes. */
         if (endswith(name, ".sh.service"))
                 return -ENOENT;
 
@@ -1193,27 +1193,32 @@ static int service_load(Unit *u) {
         assert(s);
 
         /* Load a .service file */
-        if ((r = unit_load_fragment(u)) < 0)
+        r = unit_load_fragment(u);
+        if (r < 0)
                 return r;
 
 #ifdef HAVE_SYSV_COMPAT
         /* Load a classic init script as a fallback, if we couldn't find anything */
-        if (u->load_state == UNIT_STUB)
-                if ((r = service_load_sysv(s)) < 0)
+        if (u->load_state == UNIT_STUB) {
+                r = service_load_sysv(s);
+                if (r < 0)
                         return r;
+        }
 #endif
 
         /* Still nothing found? Then let's give up */
         if (u->load_state == UNIT_STUB)
                 return -ENOENT;
 
-        /* We were able to load something, then let's add in the
-         * dropin directories. */
-        if ((r = unit_load_dropin(unit_follow_merge(u))) < 0)
-                return r;
-
         /* This is a new unit? Then let's add in some extras */
         if (u->load_state == UNIT_LOADED) {
+
+                /* We were able to load something, then let's add in
+                 * the dropin directories. */
+                r = unit_load_dropin(u);
+                if (r < 0)
+                        return r;
+
                 if (s->type == _SERVICE_TYPE_INVALID)
                         s->type = s->bus_name ? SERVICE_DBUS : SERVICE_SIMPLE;
 
@@ -3886,6 +3891,8 @@ const UnitVTable service_vtable = {
         .bus_set_property = bus_service_set_property,
         .bus_commit_properties = bus_service_commit_properties,
 
+        .can_transient = true,
+
 #ifdef HAVE_SYSV_COMPAT
         .enumerate = service_enumerate,
 #endif
diff --git a/src/core/transaction.c b/src/core/transaction.c
index fa97b69755..5259a5b7ca 100644
--- a/src/core/transaction.c
+++ b/src/core/transaction.c
@@ -851,12 +851,13 @@ int transaction_add_job_and_dependencies(
 
         if (unit->load_state != UNIT_LOADED &&
             unit->load_state != UNIT_ERROR &&
+            unit->load_state != UNIT_NOT_FOUND &&
             unit->load_state != UNIT_MASKED) {
                 dbus_set_error(e, BUS_ERROR_LOAD_FAILED, "Unit %s is not loaded properly.", unit->id);
                 return -EINVAL;
         }
 
-        if (type != JOB_STOP && unit->load_state == UNIT_ERROR) {
+        if (type != JOB_STOP && (unit->load_state == UNIT_ERROR || unit->load_state == UNIT_NOT_FOUND)) {
                 dbus_set_error(e, BUS_ERROR_LOAD_FAILED,
                                "Unit %s failed to load: %s. "
                                "See system logs and 'systemctl status %s' for details.",
diff --git a/src/core/unit.c b/src/core/unit.c
index afeb15c154..c6c9c18653 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -348,6 +348,29 @@ static void bidi_set_free(Unit *u, Set *s) {
         set_free(s);
 }
 
+static void unit_remove_transient(Unit *u) {
+        char **i;
+
+        assert(u);
+
+        if (!u->transient)
+                return;
+
+        if (u->fragment_path)
+                unlink(u->fragment_path);
+
+        STRV_FOREACH(i, u->dropin_paths) {
+                _cleanup_free_ char *p = NULL;
+                int r;
+
+                unlink(*i);
+
+                r = path_get_parent(*i, &p);
+                if (r >= 0)
+                        rmdir(p);
+        }
+}
+
 void unit_free(Unit *u) {
         UnitDependency d;
         Iterator i;
@@ -355,6 +378,9 @@ void unit_free(Unit *u) {
 
         assert(u);
 
+        if (u->manager->n_reloading <= 0)
+                unit_remove_transient(u);
+
         bus_unit_send_removed_signal(u);
 
         if (u->load_state != UNIT_STUB)
@@ -524,7 +550,7 @@ int unit_merge(Unit *u, Unit *other) {
                 return -EINVAL;
 
         if (other->load_state != UNIT_STUB &&
-            other->load_state != UNIT_ERROR)
+            other->load_state != UNIT_NOT_FOUND)
                 return -EEXIST;
 
         if (other->job)
@@ -580,7 +606,8 @@ int unit_merge_by_name(Unit *u, const char *name) {
                 name = s;
         }
 
-        if (!(other = manager_get_unit(u->manager, name)))
+        other = manager_get_unit(u->manager, name);
+        if (!other)
                 r = unit_add_name(u, name);
         else
                 r = unit_merge(u, other);
@@ -673,6 +700,7 @@ void unit_dump(Unit *u, FILE *f, const char *prefix) {
                 "%s\tInactive Enter Timestamp: %s\n"
                 "%s\tGC Check Good: %s\n"
                 "%s\tNeed Daemon Reload: %s\n"
+                "%s\tTransient: %s\n"
                 "%s\tSlice: %s\n"
                 "%s\tCGroup: %s\n"
                 "%s\tCGroup realized: %s\n"
@@ -688,6 +716,7 @@ void unit_dump(Unit *u, FILE *f, const char *prefix) {
                 prefix, strna(format_timestamp(timestamp4, sizeof(timestamp4), u->inactive_enter_timestamp.realtime)),
                 prefix, yes_no(unit_check_gc(u)),
                 prefix, yes_no(unit_need_daemon_reload(u)),
+                prefix, yes_no(u->transient),
                 prefix, strna(unit_slice_name(u)),
                 prefix, strna(u->cgroup_path),
                 prefix, yes_no(u->cgroup_realized),
@@ -903,34 +932,38 @@ int unit_load(Unit *u) {
         if (u->load_state != UNIT_STUB)
                 return 0;
 
-        if (UNIT_VTABLE(u)->load)
-                if ((r = UNIT_VTABLE(u)->load(u)) < 0)
+        if (UNIT_VTABLE(u)->load) {
+                r = UNIT_VTABLE(u)->load(u);
+                if (r < 0)
                         goto fail;
+        }
 
         if (u->load_state == UNIT_STUB) {
                 r = -ENOENT;
                 goto fail;
         }
 
-        if (u->load_state == UNIT_LOADED &&
-            u->default_dependencies)
-                if ((r = unit_add_default_dependencies(u)) < 0)
-                        goto fail;
-
         if (u->load_state == UNIT_LOADED) {
+
+                if (u->default_dependencies) {
+                        r = unit_add_default_dependencies(u);
+                        if (r < 0)
+                                goto fail;
+                }
+
                 r = unit_add_mount_links(u);
                 if (r < 0)
-                        return r;
-        }
+                        goto fail;
 
-        if (u->on_failure_isolate &&
-            set_size(u->dependencies[UNIT_ON_FAILURE]) > 1) {
+                if (u->on_failure_isolate &&
+                    set_size(u->dependencies[UNIT_ON_FAILURE]) > 1) {
 
-                log_error_unit(u->id,
-                               "More than one OnFailure= dependencies specified for %s but OnFailureIsolate= enabled. Refusing.", u->id);
+                        log_error_unit(u->id,
+                                       "More than one OnFailure= dependencies specified for %s but OnFailureIsolate= enabled. Refusing.", u->id);
 
-                r = -EINVAL;
-                goto fail;
+                        r = -EINVAL;
+                        goto fail;
+                }
         }
 
         assert((u->load_state != UNIT_MERGED) == !u->merged_into);
@@ -941,7 +974,7 @@ int unit_load(Unit *u) {
         return 0;
 
 fail:
-        u->load_state = UNIT_ERROR;
+        u->load_state = u->load_state == UNIT_STUB ? UNIT_NOT_FOUND : UNIT_ERROR;
         u->load_error = r;
         unit_add_to_dbus_queue(u);
         unit_add_to_gc_queue(u);
@@ -2117,6 +2150,11 @@ int unit_serialize(Unit *u, FILE *f, FDSet *fds, bool serialize_jobs) {
         if (dual_timestamp_is_set(&u->condition_timestamp))
                 unit_serialize_item(u, f, "condition-result", yes_no(u->condition_result));
 
+        unit_serialize_item(u, f, "transient", yes_no(u->transient));
+
+        if (u->cgroup_path)
+                unit_serialize_item(u, f, "cgroup", u->cgroup_path);
+
         /* End marker */
         fputc('\n', f);
         return 0;
@@ -2239,15 +2277,38 @@ int unit_deserialize(Unit *u, FILE *f, FDSet *fds) {
                 } else if (streq(l, "condition-result")) {
                         int b;
 
-                        if ((b = parse_boolean(v)) < 0)
+                        b = parse_boolean(v);
+                        if (b < 0)
                                 log_debug("Failed to parse condition result value %s", v);
                         else
                                 u->condition_result = b;
 
                         continue;
+
+                } else if (streq(l, "transient")) {
+                        int b;
+
+                        b = parse_boolean(v);
+                        if (b < 0)
+                                log_debug("Failed to parse transient bool %s", v);
+                        else
+                                u->transient = b;
+
+                        continue;
+                } else if (streq(l, "cgroup")) {
+                        char *s;
+
+                        s = strdup(v);
+                        if (!v)
+                                return -ENOMEM;
+
+                        free(u->cgroup_path);
+                        u->cgroup_path = s;
+                        continue;
                 }
 
-                if ((r = UNIT_VTABLE(u)->deserialize_item(u, l, v, fds)) < 0)
+                r = UNIT_VTABLE(u)->deserialize_item(u, l, v, fds);
+                if (r < 0)
                         return r;
         }
 }
@@ -2652,9 +2713,6 @@ static int drop_in_file(Unit *u, UnitSetPropertiesMode mode, const char *name, c
         assert(_q);
         assert(mode & (UNIT_PERSISTENT|UNIT_RUNTIME));
 
-        if (u->manager->running_as == SYSTEMD_USER && !(mode & UNIT_PERSISTENT))
-                return -ENOTSUP;
-
         if (!filename_is_safe(name))
                 return -EINVAL;
 
@@ -2668,7 +2726,7 @@ static int drop_in_file(Unit *u, UnitSetPropertiesMode mode, const char *name, c
                         return -ENOENT;
 
                 p = strjoin(c, "/", u->id, ".d", NULL);
-        } else  if (mode & UNIT_PERSISTENT)
+        } else if (mode & UNIT_PERSISTENT)
                 p = strjoin("/etc/systemd/system/", u->id, ".d", NULL);
         else
                 p = strjoin("/run/systemd/system/", u->id, ".d", NULL);
@@ -2741,6 +2799,43 @@ int unit_remove_drop_in(Unit *u, UnitSetPropertiesMode mode, const char *name) {
         return r;
 }
 
+int unit_make_transient(Unit *u) {
+        int r;
+
+        assert(u);
+
+        u->load_state = UNIT_STUB;
+        u->load_error = 0;
+        u->transient = true;
+
+        free(u->fragment_path);
+        u->fragment_path = NULL;
+
+        if (u->manager->running_as == SYSTEMD_USER) {
+                _cleanup_free_ char *c = NULL;
+
+                r = user_config_home(&c);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        return -ENOENT;
+
+                u->fragment_path = strjoin(c, "/", u->id, NULL);
+                if (!u->fragment_path)
+                        return -ENOMEM;
+
+                mkdir_p(c, 0755);
+        } else {
+                u->fragment_path = strappend("/run/systemd/system/", u->id);
+                if (!u->fragment_path)
+                        return -ENOMEM;
+
+                mkdir_p("/run/systemd/system", 0755);
+        }
+
+        return write_string_file_atomic_label(u->fragment_path, "# Transient stub");
+}
+
 int unit_kill_context(
                 Unit *u,
                 KillContext *c,
diff --git a/src/core/unit.h b/src/core/unit.h
index be6abaff98..8a62787b38 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -241,6 +241,9 @@ struct Unit {
         /* Did the last condition check succeed? */
         bool condition_result;
 
+        /* Is this a transient unit? */
+        bool transient;
+
         bool in_load_queue:1;
         bool in_dbus_queue:1;
         bool in_cleanup_queue:1;
@@ -425,6 +428,9 @@ struct UnitVTable {
 
         /* Exclude from automatic gc */
         bool no_gc:1;
+
+        /* True if transient units of this type are OK */
+        bool can_transient:1;
 };
 
 extern const UnitVTable * const unit_vtable[_UNIT_TYPE_MAX];
@@ -595,6 +601,8 @@ int unit_remove_drop_in(Unit *u, UnitSetPropertiesMode mode, const char *name);
 
 int unit_kill_context(Unit *u, KillContext *c, bool sigkill, pid_t main_pid, pid_t control_pid, bool main_pid_alien);
 
+int unit_make_transient(Unit *u);
+
 const char *unit_active_state_to_string(UnitActiveState i) _const_;
 UnitActiveState unit_active_state_from_string(const char *s) _pure_;