[Qgis-user] Error: ERROR: could not access file "$libdir/postgis-2.4": No such file or directory - After installing QGIS 3.10 LTR

[Neil B]

I find it odd that installing QGIS 3.10 would force an upgrade on
Postgresql to version 10.12. What version of Postgresql were you running
before? If it was a minor version of 10 before and it is still 10, then
that's trival. If it was previously a 9.X version then I wonder how your
data got migrated from the 9.X version to the 10 version automatically.

I'm guessing that the dependencies of gdal, proj, et cetera being brought
in for QGIS 3.10 probably forced an upgrade of the postgis version that's
causing the problem. The following steps are all run from the command line
as root. (Preface the command with sudo if required.)

Find out what versions of postgis for Postresql 10 are available/installed:
     apt list --all-versions | grep postgresql-10-postgis
The versions that are installed will have [installed]
or [installed,automatic] at the end. The entries for postgis-2.4 shouldn't
have anything at the end.

If you want to just fix the missing packages, then run
     apt install postgresql-10-postgis-2.4 postgresql-10-postgis-2.4-scripts
This should resolve your immediate problem and you can stop here.

Based on the earlier command, if postgis 2.5 shows up as being installed
and you want to upgrade to that version, there are several steps that need
to be done. The previous step of installing the postgis-2.4 packages still
needs to be done and you should have both the 2.4 and 2.5 packages
installed.

The extensions in Postgresql need to be upgraded and the following commands
only need to be done in the database(s) where the postgis extension has
been installed. All commands shown are run from the command line and using
psql to connect. Also assuming postgis was initially installed within
Postgresql using extensions.

Connect to the Postgresql cluster and the necessary database as the user
postgres.
The following command will provide a list of installed extensions.
     mydb=# \dx
If postgis does not show up in the list, stop. Make sure you're connected
to the correct database if you have multiple databases on that cluster. If
postgis shows up (and should say 2.4.X for the version) in the list then
proceed.
     mydb=# alter extension postgis update;
And run the following to update existing or get additional extensions
associated with that version of postgis.
     mydb=# select postgis_extensions_upgrade();
Repeat the above procedure for each database within the cluster that has
postgis extensions installed. Upgrading one database does not upgrade all
of the databases.

If everything was successful in the above steps, the postgis 2.4 packages
can be removed from the OS. Only do this if you have upgraded all databases
using postgis 2.4 to a newer version. Running as root from the command line:
     apt remove postgresql-10-postgis-2.4 postgresql-10-postgis-2.4-scripts

Not specific to this question but adding the following as thoughts for
longer term planning to anyone still using older versions of Postgresql and
Postgis.

It is best to upgrade from postgis version 2.4 or lower to either version
2.5 or version 3.0 sooner than later especially if you are planning a major
version upgrade of Postgresql. My experience is that you require
the scripts for the version of the postgis extension installed to actually
upgrade the extension within Postgresql to a newer version. Newer versions
(11 and 12) of Postgresql do not have packages in the repository for
postgis 2.4 which may cause problems if trying to update/upgrade the
postgis extensions post database upgrade.

Just an FYI Postgresql 9.5 and 9.6 will both have their final releases next
year. If you have no hard dependencies on the version of Postresql, and are
planning an upgrade, I would suggest going to Postgresql version 12 with
Postgis version 3. Postgresql 12's final release date is set for 14 Nov
2024 which will give you a few years of stability.

On Sat, May 9, 2020 at 12:53 AM Marie Anna Baovola <marieannabvl at gmail.com>
wrote:

> Hello everyone,
>
> Anyone could help me how to fix my error in my object, please?
> I have installed the QGIS 3.10 and it seems that my PostgreSQL is upgraded
> into 10.12. I use Ubuntu 18.04 bionic.
>
> I cannot reinstall the extension Postgis.
>
> Thank you in advance for your help.
>
> Best regards,
>
>
> --
> BAOVOLA Marie Anna
>
>
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