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Physical backups with pg_basebackup

Last reviewed: 2026-01-05 / Plakar v1.0.6

Overview

pg_basebackup is the standard PostgreSQL utility used to perform physical backups of a PostgreSQL cluster.
Unlike SQL dumps, a physical backup captures the entire data directory, allowing you to restore a PostgreSQL instance exactly as it was at backup time, including configuration files and internal state.

For a deeper understanding of physical backups, replication, and base backups, refer to the official PostgreSQL documentation on pg_basebackup.

Requirements

This guide assumes that you have:

  • A running PostgreSQL server configured to allow base backups.
  • A PostgreSQL role with REPLICATION privileges.
  • The environment variables PGHOST, PGPORT, PGUSER, and PGPASSWORD set to connect to your PostgreSQL server.
  • pg_basebackup available on the system where the backup is performed.

pg_hba.conf configuration

Since pg_basebackup requires replication connections, ensure that your pg_hba.conf file includes an entry allowing the backup user to connect for replication. For example:

# TYPE  DATABASE        USER            ADDRESS                 METHOD
local   replication     all                                     trust

This entry allows local replication connections without a password and should only be used in trusted environments.

Adapt the configuration to your needs and restart PostgreSQL after making changes.

Performing the backup

Directory-based backup

pg_basebackup expects a directory where the database will be copied. This directory can be stored with Plakar, like any other directory.

Run the following commands:

export PGUSER=xxx
export PGPORT=5432
export PGHOST=xxx
export PGPASSWORD=xxx

pg_basebackup -D ./database
plakar at /var/backups backup ./database
rm -rf ./database

This sequence of commands:

  • Exports the necessary environment variables to connect to the PostgreSQL server.
  • Runs pg_basebackup, storing the backup in a local directory named ./database.
  • Uses Plakar to back up the ./database directory into the Kloset store at /var/backups.
  • Removes the local backup directory to free up space.

With this method, WAL files are fetched as needed during the base backup process.

Tar-based backup

Storing the backup to an intermediate directory can be a problem, as it requires enough space to store the backup.

Alternatively, pg_basebackup can create a tarball. This tarball can be used with the tar source importer of Plakar.

export PGUSER=xxx
export PGPORT=5432
export PGHOST=xxx
export PGPASSWORD=xxx

pg_basebackup -D - -F tar -X fetch | plakar at /var/backups backup -no-progress tar:///dev/stdin

While no intermediate directory is created, this method may be slower as it requires serializing the data into a tarball stream.

Restoring a physical backup

To restore a physical backup created with pg_basebackup, use the plakar restore command to extract the backup to a local directory.

 plakar at /var/backups restore -to ./mydb 3bcb4fd8

This command restores the snapshot with ID 3bcb4fd8 from the Kloset store located at /var/backups to a local directory named ./mydb.

This command is not PostgreSQL-specific. It works for any data stored in Plakar.

Running PostgreSQL with Docker from a physical backup

With a physical backup, you can easily run a PostgreSQL instance using Docker, provided the PostgreSQL version matches the one used to create the backup.

docker run --rm -ti --name pg -v ./mydb:/var/lib/postgresql/data postgres

This command starts a PostgreSQL container using the official postgres image, mounting the restored backup directory ./mydb as the data directory for PostgreSQL.

Replace postgres with postgres:<version> to specify the desired PostgreSQL version.

To connect to the running PostgreSQL instance, use:

docker exec -ti pg psql -U postgres -c '\l'

Considerations

Physical vs logical backups

SQL dumps (pg_dump, pg_dumpall) are logical backups, portable across PostgreSQL versions and architectures.

pg_basebackup produces physical backups, which are faster to restore but must be used with a compatible PostgreSQL version and system layout.

Choose the method that best fits your recovery and portability requirements.

Read-only mounts

Plakar supports a FUSE filesystem that allows mounting a Kloset store as a read-only filesystem.

PostgreSQL requires read-write access to its data directory, even for read-only operations. Therefore, it is not possible to run PostgreSQL directly from a read-only mount of a Kloset store.

Kloset store location

In the examples above, we used /var/backups as the Kloset store location.

It is possible to use other store locations, for example to store the snapshots in a cloud storage bucket. Check the guide Create a Kloset store for more information on setting up Kloset stores.