I am following this guide to install postgres 9.3 on ubuntu 17.10, but after line of code where I actually try to install (sudo apt-get install postgresql-9.3 pgadmin3) I get the following output:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package postgresql-9.3 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'postgresql-9.3' has no installation candidate
Also, I need to install postgis, and when I type
sudo apt-get install postgresql-9.3-postgis-2.1
I got the same error. Can anyone help me?