From log:
Setting up slapd (2.4.28-1.1ubuntu4) ...
Installing new version of config file /etc/ldap/schema/misc.ldif ...
Installing new version of config file /etc/ldap/schema/cosine.ldif ...
Installing new version of config file /etc/ldap/schema/README ...
Installing new version of config file
Thank you for taking the time to report this bug and helping to make
Ubuntu better.
This looks like a local configuration problem, rather than a bug in
Ubuntu. As such, I'm marking this bug as Invalid.
You can find pointers to get help for this sort of problem here:
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https://bugs.launchpad.net/bugs/1011883
Title:
package slapd 2.4.28-1.1ubuntu4 failed to install/upgrade:
ErrorMessage: subprocess installed post-installation