Comment 12 for bug 1627304

I think this is an issue with the lightdm(-guest-session) apparmor profiles.

In dmesg:

laney@yakkety-vm:~$ dmesg | grep DENIED
[ 142.273990] audit: type=1400 audit(1474905574.718:125): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/sys/kernel/osrelease" pid=2167 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 142.274396] audit: type=1400 audit(1474905574.718:126): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/1/cmdline" pid=2167 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 142.274428] audit: type=1400 audit(1474905574.718:127): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/2/cmdline" pid=2167 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 142.274457] audit: type=1400 audit(1474905574.718:128): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/3/cmdline" pid=2167 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 142.274484] audit: type=1400 audit(1474905574.718:129): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/4/cmdline" pid=2167 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 142.274513] audit: type=1400 audit(1474905574.718:130): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/5/cmdline" pid=2167 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 142.274542] audit: type=1400 audit(1474905574.718:131): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/6/cmdline" pid=2167 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 142.274569] audit: type=1400 audit(1474905574.718:132): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/7/cmdline" pid=2167 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 142.274598] audit: type=1400 audit(1474905574.718:133): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/8/cmdline" pid=2167 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 142.274626] audit: type=1400 audit(1474905574.718:134): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/9/cmdline" pid=2167 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 147.434462] audit: type=1400 audit(1474905579.878:282): apparmor="DENIED" operation="connect" profile="/usr/lib/lightdm/lightdm-guest-session" pid=2843 comm="initctl" family="unix" sock_type="stream" protocol=0 requested_mask="send receive accept" denied_mask="send accept" addr="@/com/ubuntu/upstart-session/998/2526" peer_addr=none peer="unconfined"
[ 147.450970] audit: type=1400 audit(1474905579.894:283): apparmor="DENIED" operation="connect" profile="/usr/lib/lightdm/lightdm-guest-session" pid=2855 comm="initctl" family="unix" sock_type="stream" protocol=0 requested_mask="send receive accept" denied_mask="send accept" addr="@/com/ubuntu/upstart-session/998/2526" peer_addr=none peer="unconfined"
[ 147.494563] audit: type=1400 audit(1474905579.938:284): apparmor="DENIED" operation="connect" profile="/usr/lib/lightdm/lightdm-guest-session" pid=2871 comm="initctl" family="unix" sock_type="stream" protocol=0 requested_mask="send receive accept" denied_mask="send accept" addr="@/com/ubuntu/upstart-session/998/2526" peer_addr=none peer="unconfined"
[ 147.511922] audit: type=1400 audit(1474905579.954:285): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/sys/kernel/osrelease" pid=2879 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 147.512279] audit: type=1400 audit(1474905579.958:286): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/1/cmdline" pid=2879 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 147.512303] audit: type=1400 audit(1474905579.958:287): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/2/cmdline" pid=2879 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 147.512322] audit: type=1400 audit(1474905579.958:288): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/3/cmdline" pid=2879 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 147.512340] audit: type=1400 audit(1474905579.958:289): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/4/cmdline" pid=2879 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 147.512356] audit: type=1400 audit(1474905579.958:290): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/5/cmdline" pid=2879 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0
[ 147.512373] audit: type=1400 audit(1474905579.958:291): apparmor="DENIED" operation="open" profile="/usr/lib/lightdm/lightdm-guest-session" name="/proc/6/cmdline" pid=2879 comm="pkill" requested_mask="r" denied_mask="r" fsuid=998 ouid=0

In the journal:

Sep 26 16:59:39 yakkety-vm systemd[2518]: Starting Unity Shell v7...
Sep 26 16:59:39 yakkety-vm kernel: audit_printk_skb: 441 callbacks suppressed
Sep 26 16:59:39 yakkety-vm kernel: audit: type=1400 audit(1474905579.878:282): apparmor="DENIED" operation="connect" profile="/usr/lib/lightdm/lightdm-guest-session" pid=2843 comm="initctl" family="
Sep 26 16:59:39 yakkety-vm systemd[2518]: Started GNOME Session Manager.
Sep 26 16:59:39 yakkety-vm sh[2846]: + [ ubuntu != gnome-classic ]
Sep 26 16:59:39 yakkety-vm sh[2846]: + [ ubuntu = gnome-flashback-metacity ]
Sep 26 16:59:39 yakkety-vm sh[2846]: + exec gnome-session --session=ubuntu
Sep 26 16:59:39 yakkety-vm audit[2855]: AVC apparmor="DENIED" operation="connect" profile="/usr/lib/lightdm/lightdm-guest-session" pid=2855 comm="initctl" family="unix" sock_type="stream" protocol=0
Sep 26 16:59:39 yakkety-vm systemd-prestart-check[2845]: initctl: Unable to connect to Upstart: Failed to connect to socket /com/ubuntu/upstart-session/998/2526: Permission denied
Sep 26 16:59:39 yakkety-vm kernel: audit: type=1400 audit(1474905579.894:283): apparmor="DENIED" operation="connect" profile="/usr/lib/lightdm/lightdm-guest-session" pid=2855 comm="initctl" family="
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: OpenGL vendor string: VMware, Inc.
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: OpenGL renderer string: Gallium 0.4 on llvmpipe (LLVM 3.8, 256 bits)
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: OpenGL version string: 3.0 Mesa 12.0.1
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: Not software rendered: no
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: Not blacklisted: yes
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: GLX fbconfig: yes
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: GLX texture from pixmap: yes
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: GL npot or rect textures: yes
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: GL vertex program: yes
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: GL fragment program: yes
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: GL vertex buffer object: yes
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: GL framebuffer object: yes
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: GL version is 1.4+: yes
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: Unity 3D supported: no
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: Using compiz profile 'ubuntu-lowgfx'
Sep 26 16:59:39 yakkety-vm audit[2871]: AVC apparmor="DENIED" operation="connect" profile="/usr/lib/lightdm/lightdm-guest-session" pid=2871 comm="initctl" family="unix" sock_type="stream" protocol=0
Sep 26 16:59:39 yakkety-vm compiz-profile-selector[2861]: initctl: Unable to connect to Upstart: Failed to connect to socket /com/ubuntu/upstart-session/998/2526: Permission denied
Sep 26 16:59:39 yakkety-vm systemd[2518]: unity7.service: Control process exited, code=exited status=1
Sep 26 16:59:39 yakkety-vm systemd[2518]: Failed to start Unity Shell v7.
Sep 26 16:59:39 yakkety-vm systemd[2518]: Dependency failed for User systemd services for the Ubuntu graphical session.
Sep 26 16:59:39 yakkety-vm systemd[2518]: ubuntu-session.target: Job ubuntu-session.target/start failed with result 'dependency'.
Sep 26 16:59:39 yakkety-vm systemd[2518]: unity7.service: Unit entered failed state.
Sep 26 16:59:39 yakkety-vm kernel: audit: type=1400 audit(1474905579.938:284): apparmor="DENIED" operation="connect" profile="/usr/lib/lightdm/lightdm-guest-session" pid=2871 comm="initctl" family="
Sep 26 16:59:39 yakkety-vm systemd[2518]: unity7.service: Failed with result 'exit-code'.