Unable to install postgreSQL 9.6 in Ubuntu 18.04

I'm trying to install postgreSQL 9.6 in Ubuntu 18.04 via Ubuntu Software Centre and type from terminal

sudo apt-get install postgresql-9.6

according to official documentation

Create the file /etc/apt/sources.list.d/pgdg.list and add a line for the repository

deb bionic-pgdg main

Import the repository signing key, and update the package lists
wget --quiet -O - | sudo apt-key add -
sudo apt-get update

The version to be installaed is 10

Any help?

Thanks in advance.

postgresql:

Installed: (none) Candidate: 10+191.pgdg18.04+1 Version table: 10+191.pgdg18.04+1 500 500 bionic-pgdg/main amd64 Packages 500 bionic-pgdg/main i386 Packages 10+190 500 500 bionic/main amd64 Packages 500 bionic/main i386 Packages

If I check where are the postgresql folders, it seems that I have both versions, 9.6 and 10

/usr/lib/postgresql

2 Answers

After few months I had to erase and install from scratch, so in order to install postgresql 9.6 I followed next steps:

Important notes: If you have already installed postgresql 10 and you want 9.6, you need to remove postgresql 10 completely and then manually install postgresql 9.6, so follow method 2.

Method 1

Step 1

sudo sh -c 'echo "deb `lsb_release -cs`-pgdg main" >> /etc/apt/sources.list.d/pgdg.list' 

Step 2

wget -q -O - | sudo apt-key add - 

Step 3.

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install postgresql-9.6 

Method 2

In order to install postgres 9.6 having already postgres 10 or other version different from 9.6 installed, you need first to uninstall postgresql (any version and file related) completely following the next steps.

sudo apt-get --purge remove postgresql
dpkg -l | grep postgres (to look for postgresfiles in the system)
sudo rm -rf postgresql ... (remove all the files that appeared in the list after running the previous command)

Finally install manually postgreSQL with the next command:

sudo apt-get install postgresql-9.6

I hope it can help somebody that could have the same problem.

Not completely the same in my case when trying to replace postgresql 10 with postgresql 9.4.

I removed the old unwanted packages by

dpkg -l | grep postgres | cut -d' ' -f3 | xargs sudo apt --purge remove -y

But while I am trying to remove the packages, I also encounter several issues, I terminate the process before it reaches the 100% and the following commands are used to fix the issues along the way.

sudo lsof /var/lib/dpkg/lock-frontend
sudo kill -9 <PID>
sudo dpkg --configure -a
# if necessary, rerun the removing command above

And start the installation as:

sudo sh -c 'echo "deb `lsb_release -cs`-pgdg main" >> /etc/apt/sources.list.d/pgdg.list'
wget --quiet -O - | sudo apt-key add -
sudo apt-get update
sudo apt-get install -y postgresql-9.4