error: XDG_RUNTIME_DIR not set in the environment

[taxuezcy]

when run example ,the error is

error: XDG_RUNTIME_DIR not set in the environment. terminate called after throwing an instance of 'std::runtime_error' what(): Pangolin X11: Failed to open X display Stack trace (most recent call last):

18 Object "", at 0xffffffffffffffff, in

17 Source "/usr/include/c++/11/bits/shared_ptr_base.h", line 704, in _start [0x55dae1ec2134]

    702:       ~__shared_count() noexcept
    703:       {
  > 704:    if (_M_pi != nullptr)
    705:      _M_pi->_M_release();
    706:       }

16 Source "../csu/libc-start.c", line 392, in __libc_start_main_impl [0x7fb067d08e3f]

15 Source "../sysdeps/nptl/libc_start_call_main.h", line 58, in __libc_start_call_main [0x7fb067d08d8f]

14 Source "/home/root4/stella_vslam/example/run_video_slam.cc", line 295, in main [0x55dae1ec18a7]

    292:     // run tracking
    293:     int ret;
    294:     if (slam->get_camera()->setup_type_ == stella_vslam::camera::setup_type_t::Monocular) {
  > 295:         ret = mono_tracking(slam,
    296:                             cfg,
    297:                             video_file_path->value(),
    298:                             mask_img_path->value(),

13 Source "/home/root4/stella_vslam/example/run_video_slam.cc", line 141, in mono_tracking [0x55dae1ec3cd1]

    138:     if (!disable_gui) {
    139:         // run the viewer in the current thread
    140: #ifdef USE_PANGOLIN_VIEWER
  > 141:         viewer.run();
    142: #elif USE_SOCKET_PUBLISHER
    143:         publisher.run();
    144: #endif

12 Source "/home/root4/stella_vslam/src/pangolin_viewer/viewer.cc", line 54, in run [0x7fb069f39703]

     51: void viewer::run() {
     52:     is_terminated_ = false;
     53: 
  >  54:     pangolin::CreateWindowAndBind(map_viewer_name_, 1024, 768);
     55: 
     56:     glEnable(GL_BLEND);
     57:     glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);