当我从 Ubuntu Xenial 上的 XFCE 注销时，Lightdm 会自动登录我在 Ubuntu Xenial 上的用户。
我没有/etc/lightdm/lightdm.conf文件并且也不属于该nopasswdlogin组：
$ ls /etc/lightdm/lightdm.conf
ls: cannot access '/etc/lightdm/lightdm.conf': No such file or directory
$ groups | grep nopasswdlogin
$
EDIT0：我的默认 DM：
$ cat /etc/X11/default-display-manager
/usr/sbin/lightdm
编辑1：我有/etc/lightdm/lightdm.conf.d/10-xubuntu.conf：
$ cat /etc/lightdm/lightdm.conf.d/10-xubuntu.conf
[SeatDefaults]
user-session=xubuntu
编辑2：这是我在lightdm.service日记中的内容：
$ journalctl -au lightdm -S "2020-01-29 1:59"
-- Logs begin at lun. 2020-01-27 11:14:43 CET, end at mer. 2020-01-29 02:01:47 CET. --
janv. 29 01:59:45 sebastien-B206 lightdm[11808]: Failed to write utmpx: Permission denied
janv. 29 01:59:45 sebastien-B206 lightdm[11808]: Error writing to daemon: Bad file descriptor
janv. 29 01:59:45 sebastien-B206 lightdm[11808]: Error writing to daemon: Bad file descriptor
janv. 29 01:59:45 sebastien-B206 lightdm[11808]: Error writing to daemon: Bad file descriptor
janv. 29 01:59:45 sebastien-B206 lightdm[11808]: Failed to write utmpx: Permission denied
EDIT3：所以我刚刚重新启动了lightdm.service：
$ sudo service lightdm restart
$ service lightdm status
● lightdm.service - Light Display Manager
Loaded: loaded (/lib/systemd/system/lightdm.service; enabled; vendor preset: enabled)
Active: active (running) since Wed 2020-01-29 02:09:37 CET; 13s ago
Docs: man:lightdm(1)
Process: 15476 ExecStartPre=/bin/sh -c [ "$(basename $(cat /etc/X11/default-display-manager 2>/dev/null))" = "lightdm" ] (code=exited, status=0/SUCCESS)
Main PID: 15480 (lightdm)
CGroup: /system.slice/lightdm.service
├─15480 /usr/sbin/lightdm
├─15490 /usr/lib/xorg/Xorg -core :0 -seat seat0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch
└─15618 lightdm --session-child 12 19
Jan 29 02:09:37 sebastien-B206 systemd[1]: Starting Light Display Manager...
Jan 29 02:09:37 sebastien-B206 systemd[1]: Started Light Display Manager.
Jan 29 02:09:38 sebastien-B206 lightdm[15522]: pam_kwallet(lightdm-greeter:setcred): (null): pam_sm_setcred
Jan 29 02:09:38 sebastien-B206 lightdm[15522]: pam_kwallet5(lightdm-greeter:setcred): (null): pam_sm_setcred
Jan 29 02:09:38 sebastien-B206 lightdm[15522]: pam_unix(lightdm-greeter:session): session opened for user lightdm by (uid=0)
Jan 29 02:09:42 sebastien-B206 lightdm[15618]: pam_succeed_if(lightdm:auth): requirement "user ingroup nopasswdlogin" not met by user "sebastien"
你能帮我禁用自动登录吗？