Comment 2 for bug 1828756

Thanks for filing this bug in Ubuntu.

This is the error:
Setting up mysql-server-5.7 (5.7.26-0ubuntu0.18.04.1) ...
Installing new version of config file /etc/mysql/mysql.conf.d/mysqld.cnf ...
/var/lib/dpkg/info/mysql-server-5.7.postinst: line 191: /usr/share/mysql-common/configure-symlinks: No such file or directory
dpkg: error processing package mysql-server-5.7 (--configure):
 installed mysql-server-5.7 package post-installation script subprocess returned error exit status 127

That file (configure-symlinks) is in the mysql-common package:
$ apt-file search /usr/share/mysql-common/configure-symlinks
mysql-common: /usr/share/mysql-common/configure-symlinks

From elsewhere in your logs, we can see that you had mysql-common installed from another source, mariadb perhaps:
mysql-client-5.7 5.7.26-0ubuntu0.18.04.1
mysql-client-core-5.7 5.7.26-0ubuntu0.18.04.1
mysql-common 10.1.40+maria-1~xenial [origin: unknown]
mysql-server-core-5.7 5.7.26-0ubuntu0.18.04.1

That kind of mix is not supported. Maybe that's something you had from when you installed this machine for the first time, with xenial, and tried out mysql and mariadb, but didn't clean the installation properly before settling on one?

I will mark this bug as invalid for the time being. If you think that's a mistake and that there really is something wrong with the packaging, then please reopen the bug and state your reasons, preferably with steps to reproduce the problem.

Thanks!