src/systemctl/systemctl-switch-root.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include "bus-error.h"
   4 #include "bus-locator.h"
   5 #include "parse-util.h"
   6 #include "path-util.h"
   7 #include "proc-cmdline.h"
   8 #include "signal-util.h"
   9 #include "stat-util.h"
  10 #include "systemctl-switch-root.h"
  11 #include "systemctl-util.h"
  12 #include "systemctl.h"
  13
  14 int switch_root(int argc, char *argv[], void *userdata) {
  15         _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
  16         _cleanup_free_ char *cmdline_init = NULL;
  17         const char *root, *init;
  18         sd_bus *bus;
  19         int r;
  20
  21         if (arg_transport != BUS_TRANSPORT_LOCAL)
  22                 return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Cannot switch root remotely.");
  23
  24         if (argc < 2 || argc > 3)
  25                 return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Wrong number of arguments.");
  26
  27         root = argv[1];
  28
  29         if (argc >= 3)
  30                 init = argv[2];
  31         else {
  32                 r = proc_cmdline_get_key("init", 0, &cmdline_init);
  33                 if (r < 0)
  34                         log_debug_errno(r, "Failed to parse /proc/cmdline: %m");
  35
  36                 init = cmdline_init;
  37         }
  38
  39         init = empty_to_null(init);
  40         if (init) {
  41                 const char *root_systemd_path = NULL, *root_init_path = NULL;
  42
  43                 root_systemd_path = prefix_roota(root, "/" SYSTEMD_BINARY_PATH);
  44                 root_init_path = prefix_roota(root, init);
  45
  46                 /* If the passed init is actually the same as the systemd binary, then let's suppress it. */
  47                 if (files_same(root_init_path, root_systemd_path, 0) > 0)
  48                         init = NULL;
  49         }
  50
  51         /* Instruct PID1 to exclude us from its killing spree applied during the transition. Otherwise we
  52          * would exit with a failure status even though the switch to the new root has succeed. */
  53         assert(saved_argv);
  54         assert(saved_argv[0]);
  55         saved_argv[0][0] = '@';
  56
  57         r = acquire_bus(BUS_MANAGER, &bus);
  58         if (r < 0)
  59                 return r;
  60
  61         /* If we are slow to exit after the root switch, the new systemd instance will send us a signal to
  62          * terminate. Just ignore it and exit normally.  This way the unit does not end up as failed. */
  63         r = ignore_signals(SIGTERM, -1);
  64         if (r < 0)
  65                 log_warning_errno(r, "Failed to change disposition of SIGTERM to ignore: %m");
  66
  67         log_debug("Switching root - root: %s; init: %s", root, strna(init));
  68
  69         r = bus_call_method(bus, bus_systemd_mgr, "SwitchRoot", &error, NULL, "ss", root, init);
  70         if (r < 0) {
  71                 (void) default_signals(SIGTERM, -1);
  72
  73                 return log_error_errno(r, "Failed to switch root: %s", bus_error_message(&error, r));
  74         }
  75
  76         return 0;
  77 }