mysql database under symlinked directory: ERROR 1018 (HY000): Can't read dir of './/' (errno: 13)
It turns out that the ubuntu mysql package uses apparmor.  I found a github blog entry (no longer available a/o Oct 2019) describing my scenario and the steps to fix it, summarized below:


  Here's the gotcha: Ubuntu comes with AppArmor. AppArmor's security model is to bind access control attributes to programs rather than to users. In my /etc/apparmor.d/usr.sbin.mysqld file I've made these changes:

 # I disabled these two lines;
 # Comments indicate you don't need to
 /var/lib/mysql/ r,
 /var/lib/mysql/** rwk,
 # Added these two lines
 /example_ssd_partition/mysql/data r,
 /example_ssd_partition/mysql/data/** rwk,