I have been struggling all weekend, to upgrade an existing postgresql database from version 8.4 to 9.1. I have (had) both versions of databases after I updated my OS from 10.0.4 to 12.04.

I finally became exasperated and in a moment of lapsed judgement, I forcibly removing all 8.4 related files from my machine, using:

find / -type d -name 8.4 2>/dev/null | xargs rm -rf {}

I decided the better way to have removed it would have been `apt-get remove postgresql-8.4'

Well when I tried that, apt-get reported:

Reading package lists... Done

Building dependency tree       

Reading state information... Done

The following packages will be REMOVED:

  postgresql-8.4

0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.

1 not fully installed or removed.

After this operation, 15.5 MB disk space will be freed.

Do you want to continue [Y/n]? y

(Reading database ... 304184 files and directories currently installed.)

Removing postgresql-8.4 ...

find: `/usr/share/postgresql/8.4/tsearch_data': No such file or directory

dpkg: error processing postgresql-8.4 (--remove):

 subprocess installed pre-removal script returned error exit status 1

Errors were encountered while processing:

 postgresql-8.4

E: Sub-process /usr/bin/dpkg returned an error code (1)

How do I purge postgresql 8.4 from my machine?

[[Edit]]

After I tried apt-get install --reinstall postgresql-8.4, I get the following error:

Reading package lists... Done

Building dependency tree       

Reading state information... Done

Suggested packages:

  oidentd ident-server

The following NEW packages will be installed:

  postgresql-8.4

0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.

1 not fully installed or removed.

Need to get 0 B/5,599 kB of archives.

After this operation, 15.5 MB of additional disk space will be used.

Selecting previously unselected package postgresql-8.4.

(Reading database ... 304010 files and directories currently installed.)

Unpacking postgresql-8.4 (from .../postgresql-8.4_8.4.14-0ubuntu12.04.2_amd64.deb) ...

Setting up postgresql-client-8.4 (8.4.14-0ubuntu12.04.2) ...

update-alternatives: error: alternative path /usr/share/postgresql/8.4/man/man1/psql.1.gz doesn't exist.

dpkg: error processing postgresql-client-8.4 (--configure):

 subprocess installed post-installation script returned error exit status 2

dpkg: dependency problems prevent configuration of postgresql-8.4:

 postgresql-8.4 depends on postgresql-client-8.4; however:

  Package postgresql-client-8.4 is not configured yet.

dpkg: error processing postgresql-8.4 (--configure):

 dependency problems - leaving unconfigured

No apport report written because the error message indicates its a followup error from a previous failure.

                                                                                                          Errors were encountered while processing:

 postgresql-client-8.4

 postgresql-8.4

E: Sub-process /usr/bin/dpkg returned an error code (1)