Comment 12 for bug 1433165

I have the same problem, but the above solutions don't work:

$evince testpdf.pdf
No protocol specified

** (evince:5819): WARNING **: Could not open X display
No protocol specified
gdk_mir_display_open
Failed to connect to Mir: Failed to connect to server socket: No such file or directory
Unable to init server: Could not connect: Connection refused
Cannot parse arguments: Cannot open display:

dmesg gives:
[ 862.287951] audit: type=1400 audit(1433776649.140:49): apparmor="DENIED" operation="open" profile="/usr/bin/evince" name="/work/davids/.Xauthority" pid=5819 comm="evince" requested_mask="r" denied_mask="r" fsuid=1011 ouid=1011

$ sudo dpkg-reconfigure apparmor (with name=/work/davids/)

update-rc.d: warning: start and stop actions are no longer supported; falling back to defaults
Skipping profile in /etc/apparmor.d/disable: usr.bin.firefox
Skipping profile in /etc/apparmor.d/disable: usr.sbin.rsyslogd

Try again:

$evince testpdf.pdf
No protocol specified

** (evince:5991): WARNING **: Could not open X display
No protocol specified
gdk_mir_display_open
Failed to connect to Mir: Failed to connect to server socket: No such file or directory
Unable to init server: Could not connect: Connection refused
Cannot parse arguments: Cannot open display: