今天我注意到，每当我尝试以访客身份登录时，系统都会挂起。这种情况发生在两种情况下 - 当我尝试在登录屏幕以访客身份登录时以及当我单击右上角菜单选项“访客会话”时。
这可能很重要，因为我最近在从 14.04 升级到 15.04 时遇到了大问题 - 系统完全无法访问，我被迫使用实时 USB 和此处描述的恢复程序：https://help.ubuntu.com/community/LiveCdRecovery使系统重新启动。
这可能是什么问题？
编辑：我注意到尝试以访客身份登录会在系统日志中产生以下信息：
Jan 3 15:52:59 marek-GA-990XA-UD3 systemd[1888]: Starting Default.
Jan 3 15:52:59 marek-GA-990XA-UD3 systemd[1]: Started User Manager for UID 132.
Jan 3 15:52:59 marek-GA-990XA-UD3 kernel: [ 17.985371] audit_printk_skb: 39 callbacks suppressed
Jan 3 15:52:59 marek-GA-990XA-UD3 kernel: [ 17.985374] audit: type=1400 audit(1451832779.452:25): apparmor="DENIED" operation="create" profile="/usr/lib/lightdm/lightdm-guest-session" pid=1897 comm="xrdb" family="unix" sock_type="stream" protocol=0 requested_mask="create" denied_mask="create" addr=none
Jan 3 15:52:59 marek-GA-990XA-UD3 kernel: [ 17.998050] audit: type=1400 audit(1451832779.464:26): apparmor="DENIED" operation="create" profile="/usr/lib/lightdm/lightdm-guest-session" pid=1912 comm="id" family="unix" sock_type="stream" protocol=0 requested_mask="create" denied_mask="create" addr=none
Jan 3 15:52:59 marek-GA-990XA-UD3 kernel: [ 17.998057] audit: type=1400 audit(1451832779.464:27): apparmor="DENIED" operation="create" profile="/usr/lib/lightdm/lightdm-guest-session" pid=1912 comm="id" family="unix" sock_type="stream" protocol=0 requested_mask="create" denied_mask="create" addr=none
Jan 3 15:52:59 marek-GA-990XA-UD3 kernel: [ 17.999409] audit: type=1400 audit(1451832779.464:28): apparmor="DENIED" operation="create" profile="/usr/lib/lightdm/lightdm-guest-session" pid=1913 comm="xhost" family="unix" sock_type="stream" protocol=0 requested_mask="create" denied_mask="create" addr=none
Jan 3 15:52:59 marek-GA-990XA-UD3 kernel: [ 18.003125] audit: type=1400 audit(1451832779.468:29): apparmor="DENIED" operation="create" profile="/usr/lib/lightdm/lightdm-guest-session" pid=1916 comm="unity_support_t" family="unix" sock_type="stream" protocol=0 requested_mask="create" denied_mask="create" addr=none
Jan 3 15:52:59 marek-GA-990XA-UD3 kernel: [ 18.007685] audit: type=1400 audit(1451832779.472:30): apparmor="DENIED" operation="create" profile="/usr/lib/lightdm/lightdm-guest-session" pid=1921 comm="id" family="unix" sock_type="stream" protocol=0 requested_mask="create" denied_mask="create" addr=none
Jan 3 15:52:59 marek-GA-990XA-UD3 kernel: [ 18.007693] audit: type=1400 audit(1451832779.472:31): apparmor="DENIED" operation="create" profile="/usr/lib/lightdm/lightdm-guest-session" pid=1921 comm="id" family="unix" sock_type="stream" protocol=0 requested_mask="create" denied_mask="create" addr=none
Jan 3 15:52:59 marek-GA-990XA-UD3 kernel: [ 18.009047] audit: type=1400 audit(1451832779.476:32): apparmor="DENIED" operation="create" profile="/usr/lib/lightdm/lightdm-guest-session" pid=1922 comm="xhost" family="unix" sock_type="stream" protocol=0 requested_mask="create" denied_mask="create" addr=none
Jan 3 15:52:59 marek-GA-990XA-UD3 kernel: [ 18.013074] audit: type=1400 audit(1451832779.480:33): apparmor="DENIED" operation="create" profile="/usr/lib/lightdm/lightdm-guest-session" pid=1927 comm="xdg-user-dirs-u" family="unix" sock_type="stream" protocol=0 requested_mask="create" denied_mask="create" addr=none
Jan 3 15:52:59 marek-GA-990XA-UD3 kernel: [ 18.013081] audit: type=1400 audit(1451832779.480:34): apparmor="DENIED" operation="create" profile="/usr/lib/lightdm/lightdm-guest-session" pid=1927 comm="xdg-user-dirs-u" family="unix" sock_type="stream" protocol=0 requested_mask="create" denied_mask="create" addr=none
答案1
最有可能的是 lightdm-guest-session 文件
/etc/apparmor.d
已损坏或被删除。应该存在一个名为 lightdm-guest-session 的文件（无扩展名），其内容如下：
# vim:syntax=apparmor
# Profile for restricting lightdm guest session
#include <tunables/global>
/usr/lib/lightdm/lightdm-guest-session {
# Most applications are confined via the main abstraction
#include <abstractions/lightdm>
# chromium-browser needs special confinement due to its sandboxing
#include <abstractions/lightdm_chromium-browser> }
带有 #include 的行不是注释，但是是需要的！