Introduction

PostgreSQL is a powerful object-relational database management system, provided under a flexible BSD-style license.[1] PostgreSQL contains many advanced features, is very fast and standards compliant.

PostgreSQL has bindings for many programming languages such as C, C++, Python, Java, PHP, Ruby... It can be used to power anything from simple web applications to massive databases with millions of records.

Client Installation

If you only wish to connect to an external PostgreSQL server, do not install the main PostgreSQL package, but install the PostgreSQL client package instead. To do this, use the following command

 sudo apt-get install postgresql-client

you then connect to the server with the following command

 psql -h server.domain.org database user

After you inserted the password you access PostgreSQL with line commands. You may for instance insert the following

 SELECT * FROM table WHERE 1;

You exit the connection with

 \q

Installation

To install the server locally use the command line and type:

 sudo apt-get install postgresql postgresql-contrib

This will install the latest version available in your Ubuntu release and the commonly used add-ons for it.

See "External Links" below for options for getting newer releases.

Installing PostGIS, procedural languages, client interfaces, etc

Additional packages contain procedural language runtimes, add-ons like PostGIS, language client interfaces like psycopg2 for Python, etc. You can get a listing with:

 apt-cache search postgres

Administration

pgAdmin III is a handy GUI for PostgreSQL, it is essential to beginners. To install it, type at the command line:

 sudo apt-get install pgadmin3

You may also use the Synaptic package manager from the System>Administration menu to install these packages.

Basic Server Setup

To start off, we need to set the password of the PostgreSQL user (role) called "postgres"; we will not be able to access the server externally otherwise. As the local “postgres” Linux user, we are allowed to connect and manipulate the server using the psql command.

In a terminal, type:

sudo -u postgres psql postgres

this connects as a role with same name as the local user, i.e. "postgres", to the database called "postgres" (1st argument to psql).

Set a password for the "postgres" database role using the command:

\password postgres

and give your password when prompted. The password text will be hidden from the console for security purposes.

Type Control+D or \q to exit the posgreSQL prompt.

Create database

To create the first database, which we will call "mydb", simply type:

 sudo -u postgres createdb mydb

Install Server Instrumentation (for PgAdmin) for Postgresql 8.4 or 9.3

PgAdmin requires the installation of an add-on for full functionality. The "adminpack" addon, which it calls Server Instrumentation, is part of postgresql-contrib, so you must install that package if you haven't already:

 sudo apt-get install postgresql-contrib

Then to activate the extension, for ""Postgresql 8.4"", run the adminpack.sql script, simply type:

 sudo -u postgres psql < /usr/share/postgresql/8.4/contrib/adminpack.sql

For "Postgresql 9.3"+ install the adminpack "extension" in the "postgres" database:

 sudo -u postgres psql
 CREATE EXTENSION adminpack;

Alternative Server Setup

If you don't intend to connect to the database from other machines, this alternative setup may be simpler.

By default in Ubuntu, Postgresql is configured to use 'ident sameuser' authentication for any connections from the same machine. Check out the excellent Postgresql documentation for more information, but essentially this means that if your Ubuntu username is 'foo' and you add 'foo' as a Postgresql user then you can connect to the database without requiring a password.

Since the only user who can connect to a fresh install is the postgres user, here is how to create yourself a database account (which is in this case also a database superuser) with the same name as your login name and then create a password for the user:

 sudo -u postgres createuser --superuser $USER
 sudo -u postgres psql

 postgres=# \password $USER

Client programs, by default, connect to the local host using your Ubuntu login name and expect to find a database with that name too. So to make things REALLY easy, use your new superuser privileges granted above to create a database with the same name as your login name:

 sudo -u postgres createdb $USER

Connecting to your own database to try out some SQL should now be as easy as:

 psql

Creating additional database is just as easy, so for example, after running this:

 create database amarokdb;

You can go right ahead and tell Amarok to use postgresql to store its music catalog. The database name would be amarokdb, the username would be your own login name, and you don't even need a password thanks to 'ident sameuser' so you can leave that blank.

Using pgAdmin III GUI

To get an idea of what PostgreSQL can do, you may start by firing up a graphical client. In a terminal type :

 pgadmin3

You will be presented with the pgAdmin III interface. Click on the "Add a connection to a server" button (top left). In the new dialog, enter the address 127.0.0.1 (Local host is default, so it can be left out.), a description of the server, the default database ("mydb" in the example above), your username ("postgres") and your password. One more step is required in order to allow pgAdmin III to connect to the server, and that is to edit pg_hba.conf file and change the authentication method from peer to md5 (will not work if you have not set the password):

sudo nano /etc/postgresql/9.3/main/pg_hba.conf

and change the line

# Database administrative login by Unix domain socket
local   all             postgres                                peer

to

# Database administrative login by Unix domain socket
local   all             postgres                                md5

Now you should reload the server configuration changes and connect pgAdmin III to your PostgreSQL database server.

sudo /etc/init.d/postgresql reload

With this GUI you may start creating and managing databases, query the database, execute SQl etc.

Managing the Server

To learn more about managing PostgreSQL (but without the Ubuntu specifics) see the official PostgreSQL documentation

Managing users and rights

User management is discussed in detail in the client authentication chapter of the PostgreSQL documentation; the following is an introduction to get you started.

To manage users, you first have to edit /etc/postgresql/current/main/pg_hba.conf and modify the default configuration which is very locked down and secure. For example, if you want postgres to manage its own users (not linked with system users), you will add the following line:

8<-------------------------------------------
# TYPE  DATABASE    USER        IP-ADDRESS        IP-MASK           METHOD
host    all         all         10.0.0.0       255.255.255.0    md5
8<-------------------------------------------

Which means that on your local network (10.0.0.0/24 - replace with your own local network !), postgres users can connect through the network to the database providing a classical couple user / password.

Besides allowing a user to connect over the network to the to a database on the server, you must enable PostgreSQL to listen across different networks. To do that, open up /etc/postgresql/current/main/postgresql.conf in your favourite editor and alter the listen_addresses as below:

listen_addresses = '*'

to listen on all network interfaces. See the docs for listen_addresses for other options.

To create a database with a user that have full rights on the database, use the following command:

sudo -u postgres createuser -D -A -P myuser
sudo -u postgres createdb -O myuser mydb

The first command line creates the user with no database creation rights (-D) with no add user rights -A) and will prompt you for entering a password (-P). The second command line create the database 'mydb with 'myuser' as owner.

This little example will probably suit most of your needs. For more details, please refer to the corresponding man pages or the online documentation.

restarting the server

After configuring the networking / users you may need to reload the server, here is a suggested command to do so.

sudo /etc/init.d/postgresql reload

Some settings changes in postgresql.conf require a full restart, which will terminate active connections and abort uncommitted transactions:

sudo /etc/init.d/postgresql restart

Further reading

If you are not familiar with SQL you may want to look into this powerful language, although some simple uses of PostgreSQL may not require this knowledge (such as a simple Django project).

The PostgreSQL website contains a wealth of information on using this database. In particular, the tutorial is a useful starting point, but you can skip the installation step as you've already installed it using Ubuntu packages.

Troubleshooting

fe_sendauth: no password supplied

Your pg_hba.conf specifies that md5 authentication is to be used for this connection based on the origin host, connection method and the requested username/database, but your application didn't supply a password.

Change the authentication mode or set a password for the user you're connecting to and then specify that password in your application's connection settings.

FATAL: role "myusername" does not exist

By default PostgreSQL connects to the PostgreSQL user with the same name as the current unix user. You have not created a PostgreSQL user by that name in your database.

Create a suitable user, or specify a different username to connect with. In the command line tools the -U flag does this.

FATAL: database "myusername" does not exist

A user named "myusername" exists, but there's no database of the same name.

By default PostgreSQL connects to the database with the same name as the user you're connecting as, but it doesn't auto-create the database if it doesn't exist.

Create the database, or specify a different database to connect to.

FATAL: Peer authentication failed for user "myusername"

You are connecting to localhost via a unix socket. A user named "myusername" exists, but your current unix user is not the same as that username. PostgreSQL is set to use "peer" authentication on unix sockets for this user/db combo so it requires your unix and postgresql usernames to match.

Connect from the unix user that matches the desired PostgreSQL user - perhaps with sudo -u theusername psql - or change pg_hba.conf to use a different authentication mode like "md5" for this username.

could not connect to server: No such file or directory

An error like this (possibly with a different unix socket path, depending on your install):

 psql: could not connect to server: No such file or directory
 Is the server running locally and accepting
 connections on Unix domain socket "/tmp/.s.PGSQL.5432"?

can mean a number of things:

* The server isn't running;

* The server has a different unix_socket_directories to the default in your client's libpq, either due to different compiled-in defaults or a mismatched setting;

* The server is listening on a different "port". PostgreSQL emulates TCP/IP ports on unix sockets by using the port number as the suffix for the socket file, e.g. 5432.

Eliminate these in turn.

First make sure the server is running. On Ubuntu, ps -u postgres -f will show you any processes running as user postgres - you want to see multiple ones named postgres.

Now make sure the server is listening where your client thinks it is. To find out your PostgreSQL server's socket directory:

 sudo -u postgres psql -c "SHOW unix_socket_directories;"

or on older PostgreSQL versions, unix_socket_directory as the parameter changed name. To show the server's port (which applies for both TCP/IP and unix sockets):

 sudo -u postgres psql -c "SHOW port;"

If you can't even connect with psql under unix user postgres you can check the socket dir with lsof:

 $ sudo lsof -U -a -c postgres
 COMMAND   PID     USER   FD   TYPE             DEVICE SIZE/OFF   NODE NAME
 postgres 6565 postgres    5u  unix 0xffff88005a049f80      0t0 183009 /tmp/.s.PGSQL.5432
 postgres 6566 postgres    1u  unix 0xffff88013bc22d80      0t0 183695 socket
 postgres 6566 postgres    2u  unix 0xffff88013bc22d80      0t0 183695 socket

In this case the first line is the socket location. This server has socket directory /tmp with port 5432.

If your client is looking in a different socket directory, you're probably trying to connect over unix sockets to the default socket path and/or to the default port, and the libpq your client application is linked to has a different compiled-in unix socket path and/or port than your running PostgreSQL. Most likely your LD_LIBRARY_PATH or /etc/ld.so.conf has a different libpq before the one that came with your version of PostgreSQL. This doesn't generally matter much, you can just override the socket directory.

To specify an alternative socket directory and/port port to connect to, specify the socket dir as the host parameter in your connection options, e.g. to connect as user bob to the server listening in /tmp on port 5433:

 psql -h /tmp -p 5433 -U bob ...

or in connection-string form:

 psql "host=/tmp port=5433 user=bob ..."

The same works with any client that uses libpq (all the PostgreSQL client tools, plus e.g. psycopg2, the Pg gem in Ruby/Rails, PHP's postgres and PDO, Perl's DBB::Pg, etc). It does NOT work with non-libpq clients like PgJDBC, py-postgresql, etc, but most of these don't support unix sockets at all. See the client documentation for non-libpq based clients.


[1] You do not have to pay in order to use PostgreSQL for any application, such as commercial closed source software. See http://www.postgresql.org/about/licence/.

Official PostgreSQL downloads

The PostgreSQL project provides an official list of download locations, including an Ubuntu software repository, at its download page. In particular, Ubuntu users can get newer PostgreSQL versions than those packaged in their Ubuntu release using apt-get via apt.postgresql.org.

For support and services around PostgreSQL see the services and support page.

EnterpriseDB

The PostgreSQL Linux downloads page contains a section on "Graphical installer" built by EnterpriseDB. You download the installer, change its properties to allow to run it as command (it has .run extension), and run it from command prompt as in "sudo whateveritwas.run".

You end up with

  • configured DB server instance, which starts with your server
  • pgAdmin III UI client application

Note that the installed software will not be integrated with Ubuntu software center. As a result, you will not receive any security updates from Ubuntu. However, the installed version will closely match the latest Ubuntu version.

Turnkey Linux

An Ubuntu-based PostgreSQL appliance is one of the easiest ways to get up and running with PostgreSQL on Ubuntu. It's part of a family of pre-integrated TurnKey Linux Software Appliances based on Ubuntu 10.04.1 (Lucid LTS).

PostgreSQL (last edited 2015-08-28 13:16:48 by mikini)