package slapd 2.4.31-1+nmu2ubuntu8.3 failed to install/upgrade: subprocess new pre-installation script returned error exit status 1

Hi Rick,
thank you for taking the time to report this bug and helping to make Ubuntu better.

It seems you are upgrading "to" Trusty as version 2.4.31-1+nmu2ubuntu8.3 is trusty.
Is that a full precise to trusty Update with slapd formerly configured and working?

In the log I found a few issues, looking at them one by one:
#1
Preparing to unpack .../slapd_2.4.42+dfsg-2ubuntu3.1_amd64.deb ...
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/^(.*?)(\\)?\${ <-- HERE ([^{}]+)}(.*)$/ at /usr/share/perl5/Debconf/Question.pm line 72.

This is "just" an annoying message and fixed later on, see https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=786705. So not a problem.

#2
/tmp/ubuntu-release-upgrader-15bkpjew/imported/invoke-rc.d: 1: /tmp/ubuntu-release-upgrader-15bkpjew/imported/invoke-rc.d: /sbin/runlevel: not found
 * Stopping OpenLDAP slapd
   ...done.
  Dumping to /var/backups/slapd-2.4.31-1+nmu2ubuntu8.3:
  - directory dc=kavobv, dc=local... 58cbb2fc ldif_read_file: checksum error on "/etc/ldap/slapd.d/cn=config/olcDatabase={1}hdb.ldif"
58cbb2fc olcRootPW: value #0: <olcRootPW> can only be set when rootdn is under suffix
58cbb2fc config error processing olcDatabase={1}hdb,cn=config: <olcRootPW> can only be set when rootdn is under suffix
slapcat: bad configuration directory!
failed

That seems to have run into issues while trying to dump the DB to use it on postinst.
To do so it uses slapcat and sets a few opts.

The default is "when needed" and that is then only true if coming from before 2.4.31-1+nmu2ubuntu5 which we do in your case.

So you can trigger/test that dump manually via:
/var/lib/dpkg/info/slapd.preinst upgrade 2.4.25-1

Also enabling a set -x in that file gave me a working dump like this:
+ echo /var/backups/slapd-VERSION
+ sed -e s/VERSION/2.4.25-1/
+ dir=/var/backups/slapd-2.4.25-1
+ mkdir -p -m 700 /var/backups/slapd-2.4.25-1
+ echo /var/backups/slapd-2.4.25-1
+ dir=/var/backups/slapd-2.4.25-1
+ echo Dumping to /var/backups/slapd-2.4.25-1:
  Dumping to /var/backups/slapd-2.4.25-1:
+ + read suffix
get_suffix
+ [ -f /etc/ldap/slapd.d ]
+ + cut -d: -fgrep 2
 -h olcSuffix /etc/ldap/slapd.d/cn=config/olcDatabase={-1}frontend.ldif /etc/ldap/slapd.d/cn=config/olcDatabase={0}config.ldif /etc/ldap/slapd.d/cn=config/olcDatabase={1}hdb.ldif
+ get_directory dc=lxd
+ [ -d /etc/ldap/slapd.d ]
+ get_suffix
+ [ -f /etc/ldap/slapd.d ]
+ grep -q dc=lxd
+ cut -d: -f 2
+ grep -h olcSuffix /etc/ldap/slapd.d/cn=config/olcDatabase={-1}frontend.ldif /etc/ldap/slapd.d/cn=config/olcDatabase={0}config.ldif /etc/ldap/slapd.d/cn=config/olcDatabase={1}hdb.ldif
+ cut -d: -f 2
+ grep -l olcSuffix: dc=lxd /etc/ldap/slapd.d/cn=config/olcDatabase={-1}frontend.ldif /etc/ldap/slapd.d/cn=config/olcDatabase={0}config.ldif /etc/ldap/slapd.d/cn=config/olcDatabase={1}hdb.ldif
+ sed s/^ *//g
+ grep olcDbDirectory: /etc/ldap/slapd.d/cn=config/olcDatabase={1}hdb.ldif
+ dbdir=/var/lib/ldap
+ [ -n /var/lib/ldap ]
+ [ -d /var/lib/ldap ]
+ file=/var/backups/slapd-2.4.25-1/dc=lxd.ldif
+ echo -n - directory dc=lxd...
  - directory dc=lxd... + [ -f /etc/ldap/slapd.d ]
+ slapcat_opts=-g -F /etc/ldap/slapd.d
+ slapcat -g -F /etc...