Starting postgres on linux

TablePlus

How to start and stop PostgreSQL server?

October 30, 2018

In this post, we are going to figure out how to start, stop, and restart a PostgreSQL server on macOS, Linux, and Windows.

1. On macOS

If you installed PostgreSQL via Homebrew:

• To start PostgreSQL server now and relaunch at login:

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2. On Windows

First, you need to find the PostgreSQL database directory, it can be something like C:\Program Files\PostgreSQL\10.4\data . Then open Command Prompt and execute this command:

• Open Run Window by Winkey + R
• Type services.msc
• Search Postgres service based on version installed.
• Click stop, start or restart the service option.

3. On Linux

Update and install PostgreSQL 10.4

By default, the postgres user has no password and can hence only connect if ran by the postgres system user. The following command will assign it:

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Getting started with PostgreSQL on Linux

This post contains some introductory guidance and commands to get you started and productive with PostgreSQL in a few minutes. I’ve written it as a handy reference because I always forget most of these commands and then end up trawling the web to piece them all back together again.

Note: This was written and tested against PostgreSQL 11.7 on Debian GNU/Linux but most of it should still be generally applicable to other versions and operating systems.

Right, let’s get started!

Installation

The installation instructions below are for Debian. For other operating systems see here.

Before installing PostrgreSQL we need to run a few commands to verify that we’re installing the official package, then we can run the installation.

To do all of this, open up your terminal and enter the following commands:

Confirm you’re happy with the installation size when prompted, wait a few minutes and PostgreSQL should now be installed on your machine.

Getting started

Postgres creates a postgres super user while installing. You’ll need to switch over to this user from your current Linux user account in order to access the psql client. You can switch over to the postgres user like this:

You should now see the postgres username somewhere in your command prompt, depending on your distro. To return to your previous user from here you can just type exit .

Run psql

Psql is a tool for interacting with Postgres via the command-line. Once you’ve switched to the postgres user as per above, then you can start up psql like this:

You should now see the default postgres=# prompt, this means psql is ready to accept commands or SQL queries.

Note: This prompt is included in code examples below but you do not need to enter it as part of any commands, it’s just there for context. Some SQL query examples below won’t show this prompt because it would make the formatting of longer queries unnecessarily messy for this post .

Exit psql

To exit psql, enter the command: \q

Check version

To check what version of Postgres you’re running you can use the following:

Users

This section covers the basics on listing, creating, altering and deleting users.

List users

Create user

The above SQL query creates a user called ‘username’ with the password ‘secret123’ and gives this user permissions to create databases and users. More detail on creating users can be found here.

Alter user

This user has now had their password changed to something more secure and will become invalid just before the first second of 2021 has elapsed. It’s permissions to create databases and users have also been removed. More detail on altering users can be found here.

Delete user

If the username contains special characters then you need to enclose it in double quotes.

Databases

This section covers the basics of working with databases at a high-level. Working with tables within a database is addressed lower down.

List databases

User the command \list or \l to have a look at some of the default databases:

Create database

Let’s now create our own database called ‘mystore’:

Connect to database

to connect to a database you can use the \c command followed by the database name:

Notice that‌ your prompt now changes to reflect the name of the database you’re connected to.

Delete database

Note: you cannot delete a database that has active connections, so if you’re connected to it you’ll need to connect to another database before you can run this command.

Tables

Create table

Your new database won’t have any tables at this point, here’s an example of a query to create a table with columns of varying data types.

Below is a list of data types that you can use when creating columns.

Fixed-length character field with a limit of n. Any remaining character count in the length is padded with spaces.

Fixed-length character field with a limit of n, without padding of spaces.

Character field with no limit on characters.

BOOL or BOOLEAN

Can be true, false or NULL.

signed 2-byte integer from -32,768 to 32,767

signed 4-byte integer from -2,147,483,648 to 2,147,483,647

Same as INT except it will automatically increment the previous row’s value. This is commonly used for id fields to auto-increment the value for each new row.

floating-point number with precision of at least n up to a max of 8 bytes.

4-byte floating-point number.

NUMERIC or NUMERIC(p,s)

floating-point number with p digits before decimal point and s digits after the decimal point.

Stores date only.

Stores time of day only.

Stores date and time.

Stores date and time with timezone.

Stores periods of time.

Allows you to store an array of any valid data types. See the categories column above in the create table example that defines an array field of the TEXT data type.

Stores data as plain JSON. Slower to process than JSONB as it requires re-parsing whenever it’s processed.

Stores JSON data in binary format, slower to insert but faster to process and supports indexing.

Universally Unique Identifier has better uniqueness than SERIAL and is better for using in cases where the data is publically exposed. For example, it’s better to use UUID’s in URLs.

There is a lot more that can be done when creating tables, like creating foreign keys and so on. You can find more detail on creating tables here.

List tables

Now that you have at least one table you can list a database’s tables by being connected to it and running the \dt command.

Delete table

Insert rows

Once we’ve created a table we can then proceed to insert data into selected columns.

The indentation above is not required, however it does help to improve the readability of the query.

Select rows

Selecting all columns and rows from a table is quite straightforward.

This should produce the following output:

You can select data with conditions data more precisely like this:

which will produce an output like this:

Delete rows

Deleting rows is very similar to selecting them, you just use delete instead.

You can also use the RETURNING command to output the rows that have been deleted. In the above example, the * requests all columns for the rows to be returned but if you only wanted specific columns you could replace this with something like (username, email) .

Exporting

If you want to export a database, you can use the pg_dump tool. You’ll need to exit psql to use this. It effectively exports a file of SQL commands that when re-imported will re-create the database exactly as it was.

The below example outputs the mystore database dump into a file called ‘mystore_backup.sql’:

This is handy because you can also do things like pipe the output through your preferred compression tool into a compressed file:

Importing

To import a database dump first make sure that you’ve created a new empty database, then exit the psql client and from the command line you can use the psql command again to import the dump into your newly created database.

Okay, so that should be enough to get you started for now. Once you’re comfortable with eveything above you might want to look into creating relationships between tables using FOREIGN KEY columns and then using these to perform JOIN queries between multiple tables.

If you have any questions, comments or tips of your own, feel free to leave them below. Otherwise, I’ll update this guide in future with any more info that might be helpful here.

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YoLinux Tutorial: The PostgreSQL Database and Linux

This tutorial covers the installation and use of the PostgreSQL database on Linux This tutorial will also cover the generation and use a simple database. The interface language of the PostgreSQL database is the standard SQL (Standard Query Language) which allows for inserts, updates and queries of data stored in relational tables. The SQL language is also used for the administration of the database for the creation and modification of tables, users and access privileges. Tables are identified by unique names and hold data in a row and column (record) structure. A fixed number of named columns are defined for a table with a variable number of rows.

Characteristics favoring the PostgreSQL Database:

• Close adherence to the SQL standard
• Supports a procedural language (PL/pgSQL, PL/Tcl, PL/Perl, PL/Python) to allow for processing within the database architecture
• Extensive geospatial support (PostgreSQL is a leader in mapping and geospatial applications)

Related YoLinux Tutorials:

Ubuntu: (16.04, 14.04) Install: sudo apt-get install postgresql

• postgresql-9.X — libraries and SQL
• postgresql-common — the database program
• postgresql-client-9.X — utility programs and man pages
• postgresql-client-common — utility programs and man pages
• libpq5 — network client libraries

Starting the database: sudo service postgresql start

Red Hat Enterprise Linux 6 RPM packages:

• postgresql-8.4.11-1.el6_2.x86_64 — commands, HTML docs and man pages
• postgresql-server-8.4.11-1.el6_2.x86_64 — DB server and locale based messages
• postgresql-libs-8.4.11-1.el6_2.x86_64 — libraries and locale based messages
• postgresql-docs-8.4.11-1.el6_2.x86_64 — tutorials, examples and a monster PDF manual

Other RPM packages:

• postgresql-test — lots of examples.
• postgresql-jdbc — Java connectivity
• postgresql-plperl — Perl connectivity
• postgresql-plpython — Python connectivity
• postgresql-devel — C language connectivity

Starting the database (as root): service postgresql start

The first time this is run you will get the following error:
/var/lib/pgsql/data is missing. Use "service postgresql initdb" to initialize the cluster first.
[FAILED]

To initialize the system for the first run (as root): service postgresql initdb
Initializing database: [ OK ]

Once the database initialization has occurred, one can then start the database (as root): service postgresql restart

The user «postgres» should have already been configured by the installation of the RPMs. Info:

• User: postgres
• Home directory: /var/lib/pgsql
• Default shell: /bin/bash

A password will be missing. As root issue the command: passwd postgres to assign a password for user postgres.

• Login as user postgres: su - postgres
  This will execute the profile: /var/lib/pgsql/.bash_profile
• Initialize PostgreSQL database server: initdb --pgdata=/var/lib/pgsql/data
  This creates a bunch of directories, a template directory and sets up the postgres configuration in the user directory /var/lib/pgsql/. Red Hat start command (service)/script (rc script) will perform this task if it has not already been performed. See next step — Starting the database.

Starting the database server: As root. (from most to least favorite method)
service postgresql start
(If the database has not already been initialized with initdb, this will be performed by the command)
OR
/etc/rc.d/init.d/postgresql start
(If the database has not already been initialized with initdb, this will be performed by the script)
OR
/usr/bin/pg_ctl -D /var/lib/pgsql/data -p /usr/bin/postmaster -l logfile start &
OR
/usr/bin/postmaster -D /var/lib/pgsql/data &

Notes:

• Configuration file: /var/lib/pgsql/data/postgresql.conf
  By default there is no network access. See the directive tcpip_socket. (Required for ODBC,JDBC) Also see the postmaster directive «-i». Logging and tuning parameters are specified here.
• Host Access file: /var/lib/pgsql/data/pg_hba.conf
• Authentication/Identification file: /var/lib/pgsql/data/pg_ident.conf

• Create a database:/usr/bin/createdb bedrock
  (As Linux user postgres: sudo su - postgres)

Connect to the database:/usr/bin/psql bedrock
Execute command as Linux user postgres
You will now be at the PostgreSQL command line prompt.

Database discovery / Examine a database (as user postgres: su - postgres):
[postgres]$ psql

• \l :List databases
• \c database-name :Connect to database
• \c :Show the database your are connected to
• \d :List tables in database
• \d table-name :Describe table
• SELECT * FROM table-name :List table contents

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