Get more on UsersWikiPostGIS2 for describes how to install Postgresql 10, PostGIS 2.4, pgRouting 2.6, PGAdmin on Ubuntu.

You can use the UbuntuGIS. UbuntuGIS is a repository that can be added in your sources.list which will provide up to date GIS packages. After adding the UbuntuGIS repository corresponding to their distribution (in sources.list), you can easily install on your machine each of the GIS applications.

Verify what version of ubuntu

$ sudo lsb_release -a
sudo lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 18.04 LTS
Release:	18.04
Codename:	bionic

Add respository to sources.list

Replace ubuntu_codename with Codename from lsb_release command.

sudo sh -c 'echo "deb http://apt.postgresql.org/pub/repos/apt ubuntu_codename-pgdg main" >> /etc/apt/sources.list'

In this case is bionic (Ubuntu 18.04 LTS).

sudo sh -c 'echo "deb http://apt.postgresql.org/pub/repos/apt bionic-pgdg main" >> /etc/apt/sources.list'

Import the gpg keys and update packages

apt-key is used to manage the list of keys used by apt to authenticate packages.

wget --quiet -O - http://apt.postgresql.org/pub/repos/apt/ACCC4CF8.asc | sudo apt-key add -

sudo apt update

Install postgresql and postgis

The following will install PostgreSQL 10, PostGIS 2.4

sudo apt install postgresql-10
sudo apt install postgresql-10-postgis-2.4
sudo apt install postgresql-10-postgis-scripts
...
# pg_lsclusters
Ver Cluster Port Status Owner    Data directory              Log file
10  main    5432 online postgres /var/lib/postgresql/10/main /var/log/postgresql/postgresql-10-main.log
#

Install pgRouting

pgRouting extends the PostGIS / PostgreSQL geospatial database to provide geospatial routing functionality.

sudo apt install postgresql-10-pgrouting

Create a database and schema

The following may be executed from the SQL Shell as the postgres user:

• Create a database name is gisdb with command CREATE DATABASE
• Create a schema name is postgis with command CREATE SCHEMA. CREATE SCHEMA enters a new schema into the current database. A schema is essentially a namespace: it contains named objects (tables, data types, functions, and operators) whose names can duplicate those of other objects existing in other schemas.

postgres=# CREATE DATABASE gisdb;

postgres=#\l
                                       List of databases
       Name        |    Owner    | Encoding |   Collate   |    Ctype    |   Access privileges   
-------------------+-------------+----------+-------------+-------------+-----------------------
 finance           | postgres    | UTF8     | en_US.UTF-8 | en_US.UTF-8 |
 gisdb             | postgres    | UTF8     | en_US.UTF-8 | en_US.UTF-8 |

postgres=#\connect gisdb;

gisdb=# CREATE SCHEMA postgis;
ALTER DATABASE gisdb SET search_path=public, postgis, contrib;

Enable the postgis extension

gisdb=# CREATE EXTENSION postgis SCHEMA postgis;

Show postgis version

Reconnect the gisdb database. Use postgis_full_version() to reports full postgis version and build configuration infos.

gisdb=#SELECT postgis_full_version();
-[ RECORD 1 ]--------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
postgis_full_version | POSTGIS="2.4.3 r16312" PGSQL="100" GEOS="3.6.2-CAPI-1.10.2 4d2925d6" PROJ="Rel. 4.9.3, 15 August 2016" GDAL="GDAL 2.2.3, released 2017/11/20" LIBXML="2.9.4" LIBJSON="0.12.1" LIBPROTOBUF="1.2.1" RASTER
gisdb=#

Managing the database

Create a new postgres user (ubuntu) which we will use to connect. Replace secure_password with your password which need to use login database. Chnage owner of the gisdb database to ubuntu user and upgrade to be a superuser.

Reference to Creating a spatial database for GeoDjango Installation

The database user must be a superuser in order to run CREATE EXTENSION postgis;.The command is run during the migrate process.

# su postgres
$ psql
psql (10.3 (Ubuntu 10.3-1))
Type "help" for help.

postgres=# CREATE USER ubuntu WITH PASSWORD secure_password;
postgres=# ALTER DATABASE gisdb OWNER TO ubuntu;
postgres=# ALTER USER ubuntu WITH SUPERUSER;
postgres=# \du
List of roles
Role name |                         Attributes                         | Member of
-----------+------------------------------------------------------------+-----------
postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS | {}
ubuntu    | Superuser
postgres=# \q