1 files changed, 77 insertions, 0 deletions
diff --git a/src/systemctl/systemctl-switch-root.c b/src/systemctl/systemctl-switch-root.c
new file mode 100644
index 0000000..669fa60
--- /dev/null
+++ b/src/systemctl/systemctl-switch-root.c
@@ -0,0 +1,77 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "bus-error.h"
+#include "bus-locator.h"
+#include "parse-util.h"
+#include "path-util.h"
+#include "proc-cmdline.h"
+#include "signal-util.h"
+#include "stat-util.h"
+#include "systemctl-switch-root.h"
+#include "systemctl-util.h"
+#include "systemctl.h"
+
+int verb_switch_root(int argc, char *argv[], void *userdata) {
+        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+        _cleanup_free_ char *cmdline_init = NULL;
+        const char *root, *init;
+        sd_bus *bus;
+        int r;
+
+        if (arg_transport != BUS_TRANSPORT_LOCAL)
+                return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Cannot switch root remotely.");
+
+        if (argc < 2 || argc > 3)
+                return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Wrong number of arguments.");
+
+        root = argv[1];
+
+        if (argc >= 3)
+                init = argv[2];
+        else {
+                r = proc_cmdline_get_key("init", 0, &cmdline_init);
+                if (r < 0)
+                        log_debug_errno(r, "Failed to parse /proc/cmdline: %m");
+
+                init = cmdline_init;
+        }
+
+        init = empty_to_null(init);
+        if (init) {
+                const char *root_systemd_path = NULL, *root_init_path = NULL;
+
+                root_systemd_path = prefix_roota(root, "/" SYSTEMD_BINARY_PATH);
+                root_init_path = prefix_roota(root, init);
+
+                /* If the passed init is actually the same as the systemd binary, then let's suppress it. */
+                if (files_same(root_init_path, root_systemd_path, 0) > 0)
+                        init = NULL;
+        }
+
+        /* Instruct PID1 to exclude us from its killing spree applied during the transition. Otherwise we
+         * would exit with a failure status even though the switch to the new root has succeed. */
+        assert(saved_argv);
+        assert(saved_argv[0]);
+        saved_argv[0][0] = '@';
+
+        r = acquire_bus(BUS_MANAGER, &bus);
+        if (r < 0)
+                return r;
+
+        /* If we are slow to exit after the root switch, the new systemd instance will send us a signal to
+         * terminate. Just ignore it and exit normally.  This way the unit does not end up as failed. */
+        r = ignore_signals(SIGTERM);
+        if (r < 0)
+                log_warning_errno(r, "Failed to change disposition of SIGTERM to ignore: %m");
+
+        log_debug("Switching root - root: %s; init: %s", root, strna(init));
+
+        r = bus_call_method(bus, bus_systemd_mgr, "SwitchRoot", &error, NULL, "ss", root, init);
+        if (r < 0) {
+                (void) default_signals(SIGTERM);
+
+                return log_error_errno(r, "Failed to switch root: %s", bus_error_message(&error, r));
+        }
+
+        return 0;
+}