Back up a PostgreSQL Database with pg_dump

If you are using PostgreSQL in a production environment, it is important to take precautions to ensure that your users’ data is not lost. By frequently backing up your database, automating backups with a cron task, you can restore your system when your database is lost or corrupted. Fortunately, PostgreSQL includes tools to make this task simple and easy to manage. Learn how to backup your PostgreSQL database in Linux, in this guide.

Before You Begin

You should have a working installation of PostgreSQL on your system before beginning this guide. Go through our How to Install PostgreSQL on Ubuntu guide to install PostgreSQL and create a sample database.

One-Time SQL Dump

Single Database

PostgreSQL provides the pg_dump utility to simplify backing up a single database. This command must be run as a user with read permissions to the database you intend to back up.

1. Log in as the postgres user:

   su - postgres
   

2. Dump the contents of a database to a file by running the following command. Replace dbname with the name of the database to be backed up.

   pg_dump dbname > dbname.bak
   

   After performing the PostgreSQL load dump into a file, the resulting backup file containing the database is dbname.bak. This file can be transferred to another host with scp or stored locally for later use.

3. To demonstrate how to load a database in PostgreSQL and restore lost data, first delete your example database and then create an empty database:

   dropdb dbname
   createdb dbname
   

4. Restore the database using psql:

   psql test < dbname.bak
   

   There are several options for the backup format:

   • *.bak: compressed binary format
   • *.sql: plaintext dump
   • *.tar: tarball

After you restore a database using pg_dump, you can query the database to collect statistics about the database using:

analyze dbname

Remote Database

Just as psql allows you to connect to a remote host, pg_dump can be run from a client computer to back up data on a remote server. Use the -h flag to specify the IP address of your Linode and -p to identify the port on which PostgreSQL is listening:

pg_dump -h 198.51.100.0 -p 5432 dbname > dbname.bak

All Databases

Because pg_dump only creates a backup of one database at a time, it does not store information about database roles or other cluster-wide configuration. To store this information, and back up all of your databases simultaneously, you can use pg_dumpall.

1. Create a backup file:

   pg_dumpall > pg_backup.bak
   

2. Restore all databases from the backup:

   psql -f pg_backup.bak postgres
   

Automate Backups with a Cron Task

In this section, learn how to import a database in PostgreSQL and automate the process. To do this you need to set up a cron job so that your database backs up automatically at regular intervals. The steps in this section sets up a cron task that runs pg_dump once every week.

1. Make sure you are logged in as the postgres user:

   su - postgres
   

2. Create a directory in the postgres user’s home to store the automatic backups:

   mkdir -p ~/backups
   

3. Edit the crontab to create the new cron task:

   crontab -e
   

4. Add the following line to the end of the crontab:

   File: crontab

   1	0 0 * * 0 pg_dump -U postgres dbname > ~/postgres/backups/dbname.bak

5. Save and exit from the editor. Your database is set to back up at midnight every Sunday. To change the time or frequency of the updates, see our Schedule Tasks with Cron guide.

It is always a good idea to export a Postgres database before any major changes in structure or the installation of a new application. This applies to a Postgres import dump from a remote server.

Check PostgreSQL Backup Status

You can set up error logging to check on the status of your PostgreSQL automated backups. If you aren’t creating a log file for your PostgreSQL, create one by adding the following at the end of your cron job.

1. Make sure you are logged in as the postgres user:

   su - postgres
   

2. Create a directory in the postgres user’s home to store your error log files:

   mkdir -p ~/logs
   

3. Edit the crontab to modify the cron task:

   crontab -e
   

4. Modify the cron task line to output and append any backup errors to a log file:

   File: crontab

   1	0 0 * * 0 pg_dump -U postgres dbname > ~/backups/dbname.bak 2>> ~/logs/dbname.bak.log

5. If your system is capable of sending emails, you can also configure your cron task to send an email alert whenever there is a PostgreSQL backup error. For example, if mailx is installed and enabled for the postgres user, the following cron task sends the last line of your log file whenever an error occurs:

   File: crontab

   1	0 0 * * 0 pg_dump -U postgres dbname > ~/backups/dbname.bak 2>> ~/logs/dbname.bak.log || tail -1 ~/logs/dbname.bak.log | mailx 'example@linode.com' -s "Postgresql backup failure!"

   Now, if there are any issues with the backup, you should receive an email containing the error.

Next Steps

PostgreSQL also offers more advanced ways to back up your databases. The official docs describe how to set up continuous archiving and point-in-time recovery. This is a much more complex process, but it can maintain a constant archive of your database. You can replay PostgreSQL’s logs to recover the state of the database at any point in the past.

This method can also be helpful if you have a very large database although continuously archiving a large database consumes resources. Since the process is ongoing, there is no need to make frequent and time consuming full backups.

More Information

You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.

• PostgreSQL Documentation