我将屏幕保护程序配置为在一段时间后锁定桌面。有时，例如当我离开办公桌时，我更喜欢使用标题栏“锁定/切换帐户...”功能自己锁定屏幕。

尝试再次登录时，我输入了密码，但密码被标记为“无效”。

解决方法是，我必须使用鼠标转到标题栏中的“切换用户...”菜单，单击它，然后等待其他登录页面出现，这与屏幕保护程序锁定页面非常相似。 。（它还会列出其他用户名以供选择）

在那里，我输入相同的密码，并且密码被接受，我已经登录，出现统一桌面。

在控制台上登录也可以。

知道如何诊断和解决问题吗？

Linux xxx 3.19.0-28-generic＃30-Ubuntu SMP Mon Aug 31 15:52:51 UTC 2015 x86_64 x86_64 x86_64 GNU / Linux

团结7.3.2

Compiz 0.9.12.1

在kern.log和syslog中似乎没有任何兴趣，但是这里是/var/log/auth.log中的内容

    Sep 17 17:20:29 xxx lightdm: pam_kwallet(lightdm-greeter:setcred): pam_sm_setcred
Sep 17 17:20:29 xxx lightdm: pam_unix(lightdm-greeter:session): session opened for user lightdm by (uid=0)
Sep 17 17:20:29 xxx systemd-logind[843]: New session c13 of user lightdm.
Sep 17 17:20:29 xxx lightdm: pam_ck_connector(lightdm-greeter:session): nox11 mode, ignoring PAM_TTY :2
Sep 17 17:20:29 xxx lightdm: pam_kwallet(lightdm-greeter:session): pam_sm_open_session
Sep 17 17:20:29 xxx lightdm: pam_kwallet(lightdm-greeter:session): pam_kwallet: open_session called without kwallet_key
Sep 17 17:20:30 xxx lightdm: pam_succeed_if(lightdm:auth): requirement "user ingroup nopasswdlogin" not met by user "knb"
Sep 17 17:20:33 xxx CRON[37168]: pam_unix(cron:session): session closed for user munin
Sep 17 17:21:10 xxx lightdm: pam_kwallet(lightdm:auth): pam_sm_authenticate
Sep 17 17:21:10 xxx lightdm: pam_kwallet(lightdm:setcred): pam_sm_setcred
Sep 17 17:21:10 xxx lightdm: pam_unix(lightdm-greeter:session): session closed for user lightdm
Sep 17 17:21:10 xxx lightdm: pam_kwallet(lightdm-greeter:session): pam_sm_close_session
Sep 17 17:21:10 xxx lightdm: pam_kwallet(lightdm-greeter:setcred): pam_sm_setcred

这是我必须经过的屏幕的一些图片：

在这里，我没有输入常规密码。它仅包含ascii字符。

切换用户...（选择我自己的帐户，我不需要切换到另一个帐户）。

这行得通。

编辑：+150悬赏截止期限即将结束之前

我自己能够解决此问题（尽管遵循了所有提示和链接，但到目前为止所有〜5个答案中都包含了这些提示和链接）

I had to comment out this line in file /etc/pam.d/lightdm:

#auth sufficient pam_succeed_if.so user ingroup nopasswdlogin

I think the reason was that (many months ago, when I was the "only one" with physical access to my computer) I've added myself to the group that can login without password, and autologin to lightdn after boot/reboot. Then some day I changed this back to "login needed after reboot" but for some reason the previous no-login configuration was removed improperly from all the config files.

Now can login again :-)

A note on the bounty / "grading":

The first answerer was closest to the solution by saying something like "look closely at what's in /etc/pam.d". The answer was also the longest and the most thorough. However I checked all the other answers as valuable, that's all I can do for now, I think.