Failed to use bus name org.freedesktop.DisplayManager

I have implemented the command lightdm --test-mode --debug and I happened here such error:
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[+0.01s] DEBUG: Logging to /var/log/lightdm/lightdm.log
[+0.01s] DEBUG: Starting Light Display Manager 1.10.3, UID=0 PID=1683
[+0.01s] DEBUG: Loading configuration dirs from /var/lib/menu-xdg/lightdm/lightdm.conf.d
[+0.01s] DEBUG: Loading configuration dirs from /usr/share/gdm/lightdm/lightdm.conf.d
[+0.01s] DEBUG: Loading configuration dirs from /usr/share/lightdm/lightdm.conf.d
[+0.01s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/01_debian.conf
[+0.01s] DEBUG: Loading configuration dirs from /usr/local/share/lightdm/lightdm.conf.d
[+0.01s] DEBUG: Loading configuration dirs from /var/lib/menu-xdg/lightdm/lightdm.conf.d
[+0.01s] DEBUG: Loading configuration dirs from /usr/share/gdm/lightdm/lightdm.conf.d
[+0.01s] DEBUG: Loading configuration dirs from /usr/share/lightdm/lightdm.conf.d
[+0.01s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/01_debian.conf
[+0.01s] DEBUG: Loading configuration dirs from /usr/local/share/lightdm/lightdm.conf.d
[+0.01s] DEBUG: Loading configuration dirs from /etc/xdg/lightdm/lightdm.conf.d
[+0.01s] DEBUG: Loading configuration from /etc/lightdm/lightdm.conf
[+0.01s] DEBUG: Using D-Bus name org.freedesktop.DisplayManager
[+0.01s] DEBUG: Using Xephyr for X servers
[+0.01s] DEBUG: Registered seat module xlocal
[+0.01s] DEBUG: Registered seat module xremote
[+0.01s] DEBUG: Registered seat module unity
[+0.01s] DEBUG: Registered seat module surfaceflinger
[+1.13s] DEBUG: Adding default seat
[+1.13s] DEBUG: Seat: Starting
[+1.13s] DEBUG: Seat: Creating greeter session
[+1.17s] DEBUG: Seat: Creating display server of type x
[+1.20s] DEBUG: Could not run plymouth --ping: Failed to execute child process "plymouth" (No such file or directory)
[+1.20s] DEBUG: Using VT 7
[+1.20s] DEBUG: Seat: Starting local X display on VT 7
[+1.20s] DEBUG: DisplayServer x-1: Logging to /var/log/lightdm/x-1.log
[+1.36s] DEBUG: DisplayServer x-1: Writing X server authority to /var/run/lightdm/root/:1
[+1.36s] DEBUG: DisplayServer x-1: Launching X Server
[+1.36s] DEBUG: Launching process 1687: /usr/bin/Xephyr :1 -seat seat0 -auth /var/run/lightdm/root/:1 -nolisten tcp vt7 -novtswitch
[+1.36s] DEBUG: DisplayServer x-1: Waiting for ready signal from X server :1
[+1.36s] DEBUG: Acquired bus name org.freedesktop.DisplayManager
[+1.36s] DEBUG: Registering seat with bus path /org/freedesktop/DisplayManager/Seat0
Failed to use bus name org.freedesktop.DisplayManager, do you have appropriate permissions?
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On the Internet I have the exact solution to this problem is not found. The computer I have is only one graphics card and built-in The controller is not present. Somebody help than you can!