debian 9.7 lightdm xfce4 无法使用xdmcp

lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description: Debian GNU/Linux 9.7 (stretch)
Release: 9.7
Codename: stretch

netstat -tunlp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 504/sshd
tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN 1763/cupsd
tcp 0 0 127.0.0.1:6010 0.0.0.0:* LISTEN 2956/sshd: root@pts
tcp6 0 0 :::80 :::* LISTEN 493/apache2
tcp6 0 0 :::22 :::* LISTEN 504/sshd
tcp6 0 0 ::1:631 :::* LISTEN 1763/cupsd
tcp6 0 0 ::1:6010 :::* LISTEN 2956/sshd: root@pts
udp 0 0 0.0.0.0:631 0.0.0.0:* 1764/cups-browsed
udp 0 0 0.0.0.0:47964 0.0.0.0:* 442/avahi-daemon: r
udp 0 0 0.0.0.0:5353 0.0.0.0:* 442/avahi-daemon: r
udp6 0 0 :::33041 :::* 442/avahi-daemon: r
udp6 0 0 :::5353 :::* 442/avahi-daemon: r

/etc/lightdm/lightdm.conf
[XDMCPServer]
enabled=true
port=177
在另外一台电脑上这样配置可以看到 XDMCP 177端口已正常打开,但在这台机器上就是没有显示监听177端口。

cat lightdm.log
[+0.00s] DEBUG: Logging to /var/log/lightdm/lightdm.log
[+0.00s] DEBUG: Starting Light Display Manager 1.18.3, UID=0 PID=2023
[+0.00s] DEBUG: Loading configuration dirs from /usr/share/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/01_debian.conf
[+0.00s] DEBUG: Loading configuration dirs from /usr/local/share/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration dirs from /etc/xdg/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration from /etc/lightdm/lightdm.conf
[+0.00s] DEBUG: Using D-Bus name org.freedesktop.DisplayManager
[+0.00s] DEBUG: Using Xephyr for X servers
[+0.00s] DEBUG: Registered seat module xlocal
[+0.00s] DEBUG: Registered seat module xremote
[+0.00s] DEBUG: Registered seat module unity
[+0.02s] DEBUG: Monitoring logind for seats
[+0.02s] DEBUG: New seat added from logind: seat0
[+0.02s] DEBUG: Seat seat0: Loading properties from config section Seat:*
[+0.02s] DEBUG: Seat seat0: Starting
[+0.02s] DEBUG: Seat seat0: Creating greeter session
[+0.02s] DEBUG: Seat seat0: Creating display server of type x
[+0.02s] DEBUG: Could not run plymouth --ping: Failed to execute child process "plymouth" (No such file or directory)
[+0.02s] DEBUG: Using VT 7
[+0.02s] DEBUG: Seat seat0: Starting local X display on VT 7
[+0.02s] DEBUG: DisplayServer x-1: Logging to /var/log/lightdm/x-1.log
[+0.02s] DEBUG: DisplayServer x-1: Can't launch X server Xephyr, not found in path
[+0.02s] DEBUG: DisplayServer x-1: X server stopped
[+0.02s] DEBUG: Releasing VT 7
[+0.02s] DEBUG: Seat seat0: Display server stopped
[+0.02s] DEBUG: Seat seat0: Can't create display server for greeter
[+0.02s] DEBUG: Seat seat0: Session stopped
[+0.02s] DEBUG: Seat seat0: Stopping display server, no sessions require it
[+0.02s] DEBUG: Seat seat0: Stopping
[+0.02s] DEBUG: Seat seat0: Stopped
[+0.02s] DEBUG: Failed to start seat: seat0

 cat  Xorg.0.log
[ 17481.599]
X.Org X Server 1.19.2
Release Date: 2017-03-02
[ 17481.599] X Protocol Version 11, Revision 0
[ 17481.599] Build Operating System: Linux 4.9.0-8-amd64 x86_64 Debian
[ 17481.599] Current Operating System: Linux debian-file-stor 4.9.0-8-amd64 #1 SMP Debian 4.9.130-2 (2018-10-27) x86_64
[ 17481.599] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.9.0-8-amd64 root=UUID=0508afdb-0712-4678-8209-b058685bd4eb ro quiet
[ 17481.599] Build Date: 03 November 2018  03:09:11AM
[ 17481.599] xorg-server 2:1.19.2-1+deb9u5 
[ 17481.599] Current version of pixman: 0.34.0
[ 17481.599]    Before reporting problems, check wiki.x.org
        to make sure that you have the latest version.
[ 17481.599] Markers: (--) probed, (**) from config file, (==) default setting,
        (++) from command line, (!!) notice, (II) informational,
        (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
[ 17481.599] (==) Log file: "/var/log/Xorg.0.log", Time: Wed Feb 13 18:24:13 2019
[ 17481.599] (==) Using system config directory "/usr/share/X11/xorg.conf.d"
[ 17481.599] (==) No Layout section.  Using the first Screen section.
[ 17481.599] (==) No screen section available. Using defaults.
[ 17481.599] (**) |-->Screen "Default Screen Section" (0)
[ 17481.599] (**) |   |-->Monitor "<default monitor>"
[ 17481.599] (==) No monitor specified for screen "Default Screen Section".
        Using a default monitor configuration.
[ 17481.599] (==) Automatically adding devices
[ 17481.599] (==) Automatically enabling devices
[ 17481.599] (==) Automatically adding GPU devices
[ 17481.599] (==) Max clients allowed: 256, resource mask: 0x1fffff
[ 17481.599] (WW) The directory "/usr/share/fonts/X11/cyrillic" does not exist.
[ 17481.599]    Entry deleted from font path.
[ 17481.600] (==) FontPath set to:
        /usr/share/fonts/X11/misc,
        /usr/share/fonts/X11/100dpi/:unscaled,
        /usr/share/fonts/X11/75dpi/:unscaled,
        /usr/share/fonts/X11/Type1,
        /usr/share/fonts/X11/100dpi,
        /usr/share/fonts/X11/75dpi,
        built-ins
[ 17481.600] (==) ModulePath set to "/usr/lib/xorg/modules"
[ 17481.600] (II) The server relies on udev to provide the list of input devices.
        If no devices become available, reconfigure udev or disable AutoAddDevices.
[ 17481.600] (II) Loader magic: 0x5558e0bb7e00
[ 17481.600] (II) Module ABI versions:
[ 17481.600]    X.Org ANSI C Emulation: 0.4
[ 17481.600]    X.Org Video Driver: 23.0
[ 17481.600]    X.Org XInput driver : 24.1
[ 17481.600]    X.Org Server Extension : 10.0
[ 17481.600] (++) using VT number 7

[ 17481.600] (II) systemd-logind: logind integration requires -keeptty and -keeptty was not provided, disabling logind integration
[ 17481.601] (II) xfree86: Adding drm device (/dev/dri/card0)
[ 17481.613] (--) PCI:*(0:0:2:0) 8086:2e32:1025:038e rev 3, Mem @ 0xfe400000/4194304, 0xd0000000/268435456, I/O @ 0x0000dc00/8, BIOS @ 0x????????/131072
[ 17481.613] (II) LoadModule: "glx"
[ 17481.613] (II) Loading /usr/lib/xorg/modules/extensions/libglx.so
[ 17481.614] (II) Module glx: vendor="X.Org Foundation"
[ 17481.614]    compiled for 1.19.2, module version = 1.0.0
[ 17481.614]    ABI class: X.Org Server Extension, version 10.0
[ 17481.615] (==) Matched modesetting as autoconfigured driver 0
[ 17481.615] (==) Matched fbdev as autoconfigured driver 1
[ 17481.615] (==) Matched vesa as autoconfigured driver 2
[ 17481.615] (==) Assigned the driver to the xf86ConfigLayout
[ 17481.615] (II) LoadModule: "modesetting"
[ 17481.615] (II) Loading /usr/lib/xorg/modules/drivers/modesetting_drv.so
[ 17481.615] (II) Module modesetting: vendor="X.Org Foundation"
[ 17481.615]    compiled for 1.19.2, module version = 1.19.2
[ 17481.615]    Module class: X.Org Video Driver
[ 17481.615]    ABI class: X.Org Video Driver, version 23.0
[ 17481.615] (II) LoadModule: "fbdev"
[ 17481.615] (II) Loading /usr/lib/xorg/modules/drivers/fbdev_drv.so
[ 17481.615] (II) Module fbdev: vendor="X.Org Foundation"
[ 17481.615]    compiled for 1.19.0, module version = 0.4.4
[ 17481.615]    Module class: X.Org Video Driver
[ 17481.615]    ABI class: X.Org Video Driver, version 23.0
[ 17481.615] (II) LoadModule: "vesa"
[ 17481.615] (II) Loading /usr/lib/xorg/modules/drivers/vesa_drv.so
[ 17481.615] (II) Module vesa: vendor="X.Org Foundation"
[ 17481.615]    compiled for 1.19.0, module version = 2.3.4
[ 17481.615]    Module class: X.Org Video Driver
[ 17481.615]    ABI class: X.Org Video Driver, version 23.0
[ 17481.615] (II) modesetting: Driver for Modesetting Kernel Drivers: kms
[ 17481.616] (II) FBDEV: driver for framebuffer: fbdev
[ 17481.616] (II) VESA: driver for VESA chipsets: vesa
[ 17481.628] (II) modeset(0): using drv /dev/dri/card0
[ 17481.628] (WW) Falling back to old probe method for fbdev
[ 17481.628] (II) Loading sub module "fbdevhw"
[ 17481.628] (II) LoadModule: "fbdevhw"
[ 17481.628] (II) Loading /usr/lib/xorg/modules/libfbdevhw.so
[ 17481.628] (II) Module fbdevhw: vendor="X.Org Foundation"
[ 17481.628]    compiled for 1.19.2, module version = 0.0.2
[ 17481.628]    ABI class: X.Org Video Driver, version 23.0
[ 17481.628] (WW) Falling back to old probe method for vesa
[ 17481.628] (II) modeset(0): Creating default Display subsection in Screen section
        "Default Screen Section" for depth/fbbpp 24/32
[ 17481.628] (==) modeset(0): Depth 24, (==) framebuffer bpp 32
[ 17481.629] (==) modeset(0): RGB weight 888
[ 17481.629] (==) modeset(0): Default visual is TrueColor
[ 17481.629] (II) Loading sub module "glamoregl"
[ 17481.629] (II) LoadModule: "glamoregl"
[ 17481.629] (II) Loading /usr/lib/xorg/modules/libglamoregl.so
[ 17481.633] (II) Module glamoregl: vendor="X.Org Foundation"
[ 17481.633]    compiled for 1.19.2, module version = 1.0.0
[ 17481.633]    ABI class: X.Org ANSI C Emulation, version 0.4
[ 17481.633] (II) glamor: OpenGL accelerated X.org driver based.
[ 17481.645] (II) glamor: EGL version 1.4 (DRI2):
[ 17481.648] (II) modeset(0): glamor initialized
....