When installing Kolab on CentOS7 some packages will execute SQL queries on non-existing database. This should not happen when Kolab is not installed and setup yet.
Installing : chwala-0.5-1.1.el7.kolab_16.noarch 512/516 ERROR: SQLSTATE[HY000] [2002] No such file or directoryError 500: Error connecting to database: SQLSTATE[HY000] [2002] No such file or directory Installing : kolab-16.0.1-4.3.el7.kolab_16.x86_64 516/516 ERROR: SQLSTATE[HY000] [2002] No such file or directoryError 500: Error connecting to database: SQLSTATE[HY000] [2002] No such file or directory
https://kolab.org/hub/topic/243/kolab-16-on-centos-7-installation-issue