TL,DR: it's Apparmor's fault, and due to my home directory being outside
Under a default installation of Ubuntu 10.04, the apparmor package is pulled in as an indirect Recommends-level dependency of the ubuntu-standard package. The system logs (
/var/log/syslog) show that Apparmor is rejecting Evince's attempt to read
Jul 5 17:58:31 darkstar kernel: [15994724.481599] type=1503 audit(13415
03911.542:168): operation="open" pid=9806 parent=9805 profile="/usr/bin/evince"
requested_mask="r::" denied_mask="r::" fsuid=1001 ouid=1001 name="/elsewhere/home/gilles/.Xauthority"
The default Evince configuration for Apparmor (in
/etc/apparmor.d/usr.bin.evince) is very permissive: it allows arbitrary reads and writes under all home directories. However, my home directory on this machine is a symbolic link to non-standard location which is not listed in the default AppArmor configuration. Access is allowed under
/home, but the real location of my home directory is
/elsewhere/home/gilles, so access is denied.
Other applications that might be affected by this issue include:
- Firefox, but its profile is disabled by default (by the presence of a symbolic link
/etc/apparmor.d/disable/usr.bin.firefox -> /etc/apparmor.d/usr.bin.firefox).
- CUPS PDF printing; I haven't tested, but I expect it to fail writing to
My fix was to edit
/etc/apparmor.d/tunables/home.d/local and add the line
to have the non-standard location of home directories recognized (note that the final
/ is important; see the comments in
/etc/apparmor.d/tunables/home.d/ubuntu), then run
/etc/init.d/apparmor reload to update the Apparmor settings.
If you don't have administrator privileges and the system administrator is unresponsive, you can copy the
evince binary to a different location such as
~/bin, and it won't be covered by the Apparmor policy (so you'll be able to start it, but will not be afforded the very limited extra security that Apparmor provides).
This issue has been reported as Ubuntu bug #447292. The resolution handles the case when some users have their home directory as listed in
/home, but not cases such as mine where
/home/gilles is a symbolic link.