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Today I noticed that whenever I try to log into as a guest, the system hangs. This happens in both cases - when I try to log-in as guest in log-in screen and when I click "Guest session" upper-right corner menu option.

It might be important that I recently had big problem with upgrade from 14.04 to 15.04 - the system was completely inaccessible and I was forced to use live USB and a recovery procedure described here: https://help.ubuntu.com/community/LiveCdRecovery to make system start again.

What could be the problem here?

EDIT: I noticed that the attempt to log in as a guest produces this in syslog:

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
  • Do you have any customization files in /etc/guest-session? – Gunnar Hjalmarsson Dec 19 '15 at 12:07
  • @GunnarHjalmarsson I don't even have /etc/guest-session directory. Should I? – Marek Lipka Dec 19 '15 at 15:31
  • No, it's optional. ;) But then we know that the cause is not such a badly configured file. – Gunnar Hjalmarsson Dec 19 '15 at 23:37
  • Does your root partition (,/ and /tmp ) have enough free space? – totti Jan 3 '16 at 14:43
  • @totti yes, it does. But I edited my question with a syslog fragment that can be relevant. – Marek Lipka Jan 3 '16 at 15:05
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+50

Most likely the lightdm-guest-session file in

/etc/apparmor.d

has been corrupted or been deleted. There should be a file present named lightdm-guest-session without extension and with the following inside:

# 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>  }

The lines with #include are not comments but needed!

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