BackRest takes some command-line parameters, but depends on a configuration file for most of the settings. The default location for the configuration file is /etc/pg_backrest.conf.
### configuration examples
#### Simple single host install
This configuration is appropriate for a small installation where backups are being made locally or to a remote file system that is mounted locally.
Each section defines important aspects of the backup. All configuration sections below should be prefixed with "global:" as demonstrated in the configuration samples.
#### command section
The command section defines external commands that are used by BackRest.
##### psql key
Defines the full path to psql. psql is used to call pg_start_backup() and pg_stop_backup().
_required_: y
_example_: psql=/usr/bin/psql
##### remote key
Defines the file path to pg_backrest_remote.pl.
Required only if the path to pg_backrest_remote.pl is different on the local and remote systems. If not defined, the remote path will be assumed to be the same as the local path.
Defines the number of threads to use for backup. Each thread will perform compression and transfer to make the backup run faster, but don't set `thread-max` so high that it impacts database performance.
Maximum amount of time that a backup thread should run. This limits the amount of time that a thread might be stuck due to unforeseen issues during the backup.
_default_: <none>
_example_: thread-max=4
##### archive-required
Are archive logs required to to complete the backup? It's a good idea to leave this as the default unless you are using another
method for archiving.
_default_: y
_example_: archive-required=n
#### archive section
The archive section defines parameters when doing async archiving. This means that the archive files will be stored locally, then a background process will pick them and move them to the backup.
##### path
Path where archive logs are stored before being asynchronously transferred to the backup. Make sure this is not the same path as the backup is using if the backup is local.
_required_: y
_example_: path=/backup/archive
##### compress-async
When set then archive logs are not compressed immediately, but are instead compressed when copied to the backup host. This means that more space will be used on local storage, but the initial archive process will complete more quickly allowing greater throughput from Postgres.
_default_: n
_example_: compress-async=y
##### archive-max-mb
Limits the amount of archive log that will be written locally. After the limit is reached, the following will happen:
1. BackRest will notify Postgres that the archive was succesfully backed up, then DROP IT.
2. An error will be logged to the console and also to the Postgres log.
3. A stop file will be written in the lock directory and no more archive files will be backed up until it is removed.
If this occurs then the archive log stream will be interrupted and PITR will not be possible past that point. A new backup will be required to regain full restore capability.
The purpose of this feature is to prevent the log volume from filling up at which point Postgres will stop all operation. Better to lose the backup than have the database go down completely.
To start normal archiving again you'll need to remove the stop file which will be located at `${archive-path}/lock/${stanza}-archive.stop` where `${archive-path}` is the path set in the archive section, and ${stanza} is the backup stanza.
_required_: n
_example_: archive-max-mb=1024
#### retention section
The rentention section defines how long backups will be retained. Expiration only occurs when the number of complete backups exceeds the allowed retention. In other words, if full-retention is set to 2, then there must be 3 complete backups before the oldest will be expired. Make sure you always have enough space for rentention + 1 backups.
##### full-retention
Number of full backups to keep. When a full backup expires, all differential and incremental backups associated with the full backup will also expire. When not defined then all full backups will be kept.
_required_: n
_example_: full-retention=2
##### differential-retention
Number of differential backups to keep. When a differential backup expires, all incremental backups associated with the differential backup will also expire. When not defined all differential backups will be kept.
_required_: n
_example_: differential-retention=3
##### archive-retention-type
Type of backup to use for archive retention (full or differential). If set to full, then BackRest will keep archive logs for the number of full backups defined by `archive-retention`. If set to differential, then BackRest will keep archive logs for the number of differential backups defined by `archive-retention`.
If not defined then archive logs will be kept indefinitely. In general it is not useful to keep archive logs that are older than the oldest backup, but there may be reasons for doing so.
_required_: n
_example_: archive-retention-type=full
##### archive-retention
Number of backups worth of archive log to keep. If not defined, then `full-retention` will be used when `archive-retention-type=full` and `differential-retention` will be used when `archive-retention-type=differential`.
_required_: n
_example_: archive-retention=2
### stanza sections
A stanza defines a backup for a specific database. The stanza section must define the base database path and host/user if the database is remote. Also, any global configuration sections can be overridden to define stanza-specific settings.
##### host
Sets the database host.
* _required_: n (but must be set if user is defined)
* _example_: host=db.mydomain.com
##### user
Sets user account on the db host.
* _required_: n (but must be set if host is defined)
* _example_: user=postgres
##### path
Path to the db data directory (data_directory setting in postgresql.conf).
