pg\_basebackup

pg\_basebackup

1

Application

pg\_basebackup

take a base backup of a

PostgreSQL

cluster

pg\_basebackup

option

Description
===========

pg\_basebackup is used to take a base backup of a running PostgreSQL
database cluster. The backup is taken without affecting other clients of
the database, and can be used both for point-in-time recovery (see
[???](#continuous-archiving)) and as the starting point for a
log-shipping or streaming-replication standby server (see
[???](#warm-standby)).

pg\_basebackup makes an exact copy of the database cluster\'s files,
while making sure the server is put into and out of backup mode
automatically. Backups are always taken of the entire database cluster;
it is not possible to back up individual databases or database objects.
For selective backups, another tool such as [???](#app-pgdump) must be
used.

The backup is made over a regular PostgreSQL connection that uses the
replication protocol. The connection must be made with a user ID that
has `REPLICATION` permissions (see [???](#role-attributes)) or is a
superuser, and [`pg_hba.conf`](#auth-pg-hba-conf) must permit the
replication connection. The server must also be configured with
[???](#guc-max-wal-senders) set high enough to provide at least one
walsender for the backup plus one for WAL streaming (if used).

There can be multiple `pg_basebackup`s running at the same time, but it
is usually better from a performance point of view to take only one
backup, and copy the result.

pg\_basebackup can make a base backup from not only a primary server but
also a standby. To take a backup from a standby, set up the standby so
that it can accept replication connections (that is, set
`max_wal_senders` and [???](#guc-hot-standby), and configure its
`pg_hba.conf` appropriately). You will also need to enable
[???](#guc-full-page-writes) on the primary.

Note that there are some limitations in taking a backup from a standby:

-   The backup history file is not created in the database cluster
    backed up.

-   pg\_basebackup cannot force the standby to switch to a new WAL file
    at the end of backup. When you are using `-X none`, if write
    activity on the primary is low, pg\_basebackup may need to wait a
    long time for the last WAL file required for the backup to be
    switched and archived. In this case, it may be useful to run
    `pg_switch_wal` on the primary in order to trigger an immediate WAL
    file switch.

-   If the standby is promoted to be primary during backup, the backup
    fails.

-   All WAL records required for the backup must contain sufficient
    full-page writes, which requires you to enable `full_page_writes` on
    the primary and not to use a tool in your `archive_library` to
    remove full-page writes from WAL files.

Whenever pg\_basebackup is taking a base backup, the server\'s
pg\_stat\_progress\_basebackup view will report the progress of the
backup. See [???](#basebackup-progress-reporting) for details.

Options
=======

The following command-line options control the location and format of
the output:

`-D directory`; `--pgdata=directory`

:   Sets the target directory to write the output to. pg\_basebackup
    will create this directory (and any missing parent directories) if
    it does not exist. If it already exists, it must be empty.

    When the backup is in tar format, the target directory may be
    specified as `-` (dash), causing the tar file to be written to
    `stdout`.

    This option is required.

`-F format`; `--format=format`

:   Selects the format for the output. format can be one of the
    following:

    `p`; `plain`

    :   Write the output as plain files, with the same layout as the
        source server\'s data directory and tablespaces. When the
        cluster has no additional tablespaces, the whole database will
        be placed in the target directory. If the cluster contains
        additional tablespaces, the main data directory will be placed
        in the target directory, but all other tablespaces will be
        placed in the same absolute path as they have on the source
        server. (See `--tablespace-mapping` to change that.)

        This is the default format.

    `t`; `tar`

    :   Write the output as tar files in the target directory. The main
        data directory\'s contents will be written to a file named
        `base.tar`, and each other tablespace will be written to a
        separate tar file named after that tablespace\'s OID.

        If the target directory is specified as `-` (dash), the tar
        contents will be written to standard output, suitable for piping
        to (for example) gzip. This is only allowed if the cluster has
        no additional tablespaces and WAL streaming is not used.

`-R`; `--write-recovery-conf`

:   Creates a [`standby.signal`](#file-standby-signal)
    `standby.signal`pg\_basebackup \--write-recovery-conf file and
    appends connection settings to the `postgresql.auto.conf` file in
    the target directory (or within the base archive file when using tar
    format). This eases setting up a standby server using the results of
    the backup.

    The `postgresql.auto.conf` file will record the connection settings
    and, if specified, the replication slot that pg\_basebackup is
    using, so that streaming replication will use the same settings
    later on.

`-t target`; `--target=target`

:   Instructs the server where to place the base backup. The default
    target is `client`, which specifies that the backup should be sent
    to the machine where pg\_basebackup is running. If the target is
    instead set to `server:/some/path`, the backup will be stored on the
    machine where the server is running in the `/some/path` directory.
    Storing a backup on the server requires superuser privileges or
    having privileges of the `pg_write_server_files` role. If the target
    is set to `blackhole`, the contents are discarded and not stored
    anywhere. This should only be used for testing purposes, as you will
    not end up with an actual backup.

    Since WAL streaming is implemented by pg\_basebackup rather than by
    the server, this option cannot be used together with `-Xstream`.
    Since that is the default, when this option is specified, you must
    also specify either `-Xfetch` or `-Xnone`.

`-T olddir=newdir`; `--tablespace-mapping=olddir=newdir`

:   Relocates the tablespace in directory olddir to newdir during the
    backup. To be effective, olddir must exactly match the path
    specification of the tablespace as it is defined on the source
    server. (But it is not an error if there is no tablespace in olddir
    on the source server.) Meanwhile newdir is a directory in the
    receiving host\'s filesystem. As with the main target directory,
    newdir need not exist already, but if it does exist it must be
    empty. Both olddir and newdir must be absolute paths. If either path
    needs to contain an equal sign (`=`), precede that with a backslash.
    This option can be specified multiple times for multiple
    tablespaces.

    If a tablespace is relocated in this way, the symbolic links inside
    the main data directory are updated to point to the new location. So
    the new data directory is ready to be used for a new server instance
    with all tablespaces in the updated locations.

    Currently, this option only works with plain output format; it is
    ignored if tar format is selected.

`--waldir=waldir`

:   Sets the directory to write WAL (write-ahead log) files to. By
    default WAL files will be placed in the `pg_wal` subdirectory of the
    target directory, but this option can be used to place them
    elsewhere. waldir must be an absolute path. As with the main target
    directory, waldir need not exist already, but if it does exist it
    must be empty. This option can only be specified when the backup is
    in plain format.

`-X method`; `--wal-method=method`

:   Includes the required WAL (write-ahead log) files in the backup.
    This will include all write-ahead logs generated during the backup.
    Unless the method `none` is specified, it is possible to start a
    postmaster in the target directory without the need to consult the
    log archive, thus making the output a completely standalone backup.

    The following methods for collecting the write-ahead logs are
    supported:

    `n`; `none`

    :   Don\'t include write-ahead logs in the backup.

    `f`; `fetch`

    :   The write-ahead log files are collected at the end of the
        backup. Therefore, it is necessary for the source server\'s
        [???](#guc-wal-keep-size) parameter to be set high enough that
        the required log data is not removed before the end of the
        backup. If the required log data has been recycled before it\'s
        time to transfer it, the backup will fail and be unusable.

        When tar format is used, the write-ahead log files will be
        included in the `base.tar` file.

    `s`; `stream`

    :   Stream write-ahead log data while the backup is being taken.
        This method will open a second connection to the server and
        start streaming the write-ahead log in parallel while running
        the backup. Therefore, it will require two replication
        connections not just one. As long as the client can keep up with
        the write-ahead log data, using this method requires no extra
        write-ahead logs to be saved on the source server.

        When tar format is used, the write-ahead log files will be
        written to a separate file named `pg_wal.tar` (if the server is
        a version earlier than 10, the file will be named
        `pg_xlog.tar`).

        This value is the default.

`-z`; `--gzip`

:   Enables gzip compression of tar file output, with the default
    compression level. Compression is only available when using the tar
    format, and the suffix `.gz` will automatically be added to all tar
    filenames.

`-Z level`; `-Z [{client|server}-]method[:detail]`; `--compress=level`; `--compress=[{client|server}-]method[:detail]`

:   Requests compression of the backup. If `client` or `server` is
    included, it specifies where the compression is to be performed.
    Compressing on the server will reduce transfer bandwidth but will
    increase server CPU consumption. The default is `client` except when
    `--target` is used. In that case, the backup is not being sent to
    the client, so only server compression is sensible. When `-Xstream`,
    which is the default, is used, server-side compression will not be
    applied to the WAL. To compress the WAL, use client-side
    compression, or specify `-Xfetch`.

    The compression method can be set to `gzip`, `lz4`, `zstd`, or
    `none` for no compression. A compression detail string can
    optionally be specified. If the detail string is an integer, it
    specifies the compression level. Otherwise, it should be a
    comma-separated list of items, each of the form `keyword` or
    `keyword=value`. Currently, the supported keywords are `level` and
    `workers`.

    If no compression level is specified, the default compression level
    will be used. If only a level is specified without mentioning an
    algorithm, `gzip` compression will be used if the level is greater
    than 0, and no compression will be used if the level is 0.

    When the tar format is used with `gzip`, `lz4`, or `zstd`, the
    suffix `.gz`, `.lz4`, or `.zst`, respectively, will be automatically
    added to all tar filenames. When the plain format is used,
    client-side compression may not be specified, but it is still
    possible to request server-side compression. If this is done, the
    server will compress the backup for transmission, and the client
    will decompress and extract it.

    When this option is used in combination with `-Xstream`,
    `pg_wal.tar` will be compressed using `gzip` if client-side gzip
    compression is selected, but will not be compressed if any other
    compression algorithm is selected, or if server-side compression is
    selected.

The following command-line options control the generation of the backup
and the invocation of the program:

`-c {fast|spread}`; `--checkpoint={fast|spread}`

:   Sets checkpoint mode to fast (immediate) or spread (the default)
    (see [???](#backup-lowlevel-base-backup)).

`-C`; `--create-slot`

:   Specifies that the replication slot named by the `--slot` option
    should be created before starting the backup. An error is raised if
    the slot already exists.

`-l label`; `--label=label`

:   Sets the label for the backup. If none is specified, a default value
    of "`pg_basebackup base backup`" will be used.

`-n`; `--no-clean`

:   By default, when `pg_basebackup` aborts with an error, it removes
    any directories it might have created before discovering that it
    cannot finish the job (for example, the target directory and
    write-ahead log directory). This option inhibits tidying-up and is
    thus useful for debugging.

    Note that tablespace directories are not cleaned up either way.

`-N`; `--no-sync`

:   By default, `pg_basebackup` will wait for all files to be written
    safely to disk. This option causes `pg_basebackup` to return without
    waiting, which is faster, but means that a subsequent operating
    system crash can leave the base backup corrupt. Generally, this
    option is useful for testing but should not be used when creating a
    production installation.

`-P`; `--progress`

:   Enables progress reporting. Turning this on will deliver an
    approximate progress report during the backup. Since the database
    may change during the backup, this is only an approximation and may
    not end at exactly `100%`. In particular, when WAL log is included
    in the backup, the total amount of data cannot be estimated in
    advance, and in this case the estimated target size will increase
    once it passes the total estimate without WAL.

`-r rate`; `--max-rate=rate`

:   Sets the maximum transfer rate at which data is collected from the
    source server. This can be useful to limit the impact of
    pg\_basebackup on the server. Values are in kilobytes per second.
    Use a suffix of `M` to indicate megabytes per second. A suffix of
    `k` is also accepted, and has no effect. Valid values are between 32
    kilobytes per second and 1024 megabytes per second.

    This option always affects transfer of the data directory. Transfer
    of WAL files is only affected if the collection method is `fetch`.

`-S slotname`; `--slot=slotname`

:   This option can only be used together with `-X
            stream`. It causes WAL streaming to use the specified
    replication slot. If the base backup is intended to be used as a
    streaming-replication standby using a replication slot, the standby
    should then use the same replication slot name as
    [???](#guc-primary-slot-name). This ensures that the primary server
    does not remove any necessary WAL data in the time between the end
    of the base backup and the start of streaming replication on the new
    standby.

    The specified replication slot has to exist unless the option `-C`
    is also used.

    If this option is not specified and the server supports temporary
    replication slots (version 10 and later), then a temporary
    replication slot is automatically used for WAL streaming.

`-v`; `--verbose`

:   Enables verbose mode. Will output some extra steps during startup
    and shutdown, as well as show the exact file name that is currently
    being processed if progress reporting is also enabled.

`--manifest-checksums=algorithm`

:   Specifies the checksum algorithm that should be applied to each file
    included in the backup manifest. Currently, the available algorithms
    are `NONE`, `CRC32C`, `SHA224`, `SHA256`, `SHA384`, and `SHA512`.
    The default is `CRC32C`.

    If `NONE` is selected, the backup manifest will not contain any
    checksums. Otherwise, it will contain a checksum of each file in the
    backup using the specified algorithm. In addition, the manifest will
    always contain a `SHA256` checksum of its own contents. The `SHA`
    algorithms are significantly more CPU-intensive than `CRC32C`, so
    selecting one of them may increase the time required to complete the
    backup.

    Using a SHA hash function provides a cryptographically secure digest
    of each file for users who wish to verify that the backup has not
    been tampered with, while the CRC32C algorithm provides a checksum
    that is much faster to calculate; it is good at catching errors due
    to accidental changes but is not resistant to malicious
    modifications. Note that, to be useful against an adversary who has
    access to the backup, the backup manifest would need to be stored
    securely elsewhere or otherwise verified not to have been modified
    since the backup was taken.

    [???](#app-pgverifybackup) can be used to check the integrity of a
    backup against the backup manifest.

`--manifest-force-encode`

:   Forces all filenames in the backup manifest to be hex-encoded. If
    this option is not specified, only non-UTF8 filenames are
    hex-encoded. This option is mostly intended to test that tools which
    read a backup manifest file properly handle this case.

`--no-estimate-size`

:   Prevents the server from estimating the total amount of backup data
    that will be streamed, resulting in the backup\_total column in the
    pg\_stat\_progress\_basebackup view always being `NULL`.

    Without this option, the backup will start by enumerating the size
    of the entire database, and then go back and send the actual
    contents. This may make the backup take slightly longer, and in
    particular it will take longer before the first data is sent. This
    option is useful to avoid such estimation time if it\'s too long.

    This option is not allowed when using `--progress`.

`--no-manifest`

:   Disables generation of a backup manifest. If this option is not
    specified, the server will generate and send a backup manifest which
    can be verified using [???](#app-pgverifybackup). The manifest is a
    list of every file present in the backup with the exception of any
    WAL files that may be included. It also stores the size, last
    modification time, and an optional checksum for each file.

`--no-slot`

:   Prevents the creation of a temporary replication slot for the
    backup.

    By default, if log streaming is selected but no slot name is given
    with the `-S` option, then a temporary replication slot is created
    (if supported by the source server).

    The main purpose of this option is to allow taking a base backup
    when the server has no free replication slots. Using a replication
    slot is almost always preferred, because it prevents needed WAL from
    being removed by the server during the backup.

`--no-verify-checksums`

:   Disables verification of checksums, if they are enabled on the
    server the base backup is taken from.

    By default, checksums are verified and checksum failures will result
    in a non-zero exit status. However, the base backup will not be
    removed in such a case, as if the `--no-clean` option had been used.
    Checksum verification failures will also be reported in the
    [pg\_stat\_database](#monitoring-pg-stat-database-view) view.

The following command-line options control the connection to the source
server:

`-d connstr`; `--dbname=connstr`

:   Specifies parameters used to connect to the server, as a [connection
    string](#libpq-connstring); these will override any conflicting
    command line options.

    The option is called `--dbname` for consistency with other client
    applications, but because pg\_basebackup doesn\'t connect to any
    particular database in the cluster, any database name in the
    connection string will be ignored.

`-h host`; `--host=host`

:   Specifies the host name of the machine on which the server is
    running. If the value begins with a slash, it is used as the
    directory for a Unix domain socket. The default is taken from the
    PGHOST environment variable, if set, else a Unix domain socket
    connection is attempted.

`-p port`; `--port=port`

:   Specifies the TCP port or local Unix domain socket file extension on
    which the server is listening for connections. Defaults to the
    PGPORT environment variable, if set, or a compiled-in default.

`-s interval`; `--status-interval=interval`

:   Specifies the number of seconds between status packets sent back to
    the source server. Smaller values allow more accurate monitoring of
    backup progress from the server. A value of zero disables periodic
    status updates completely, although an update will still be sent
    when requested by the server, to avoid timeout-based disconnects.
    The default value is 10 seconds.

`-U username`; `--username=username`

:   Specifies the user name to connect as.

`-w`; `--no-password`

:   Prevents issuing a password prompt. If the server requires password
    authentication and a password is not available by other means such
    as a `.pgpass` file, the connection attempt will fail. This option
    can be useful in batch jobs and scripts where no user is present to
    enter a password.

`-W`; `--password`

:   Forces pg\_basebackup to prompt for a password before connecting to
    the source server.

    This option is never essential, since pg\_basebackup will
    automatically prompt for a password if the server demands password
    authentication. However, pg\_basebackup will waste a connection
    attempt finding out that the server wants a password. In some cases
    it is worth typing `-W` to avoid the extra connection attempt.

Other options are also available:

`-V`; `--version`

:   Prints the pg\_basebackup version and exits.

`-?`; `--help`

:   Shows help about pg\_basebackup command line arguments, and exits.

Environment
===========

This utility, like most other PostgreSQL utilities, uses the environment
variables supported by libpq (see [???](#libpq-envars)).

The environment variable PG\_COLOR specifies whether to use color in
diagnostic messages. Possible values are `always`, `auto` and `never`.

Notes
=====

At the beginning of the backup, a checkpoint needs to be performed on
the source server. This can take some time (especially if the option
`--checkpoint=fast` is not used), during which pg\_basebackup will
appear to be idle.

The backup will include all files in the data directory and tablespaces,
including the configuration files and any additional files placed in the
directory by third parties, except certain temporary files managed by
PostgreSQL. But only regular files and directories are copied, except
that symbolic links used for tablespaces are preserved. Symbolic links
pointing to certain directories known to PostgreSQL are copied as empty
directories. Other symbolic links and special device files are skipped.
See [???](#protocol-replication) for the precise details.

In plain format, tablespaces will be backed up to the same path they
have on the source server, unless the option `--tablespace-mapping` is
used. Without this option, running a plain format base backup on the
same host as the server will not work if tablespaces are in use, because
the backup would have to be written to the same directory locations as
the original tablespaces.

When tar format is used, it is the user\'s responsibility to unpack each
tar file before starting a PostgreSQL server that uses the data. If
there are additional tablespaces, the tar files for them need to be
unpacked in the correct locations. In this case the symbolic links for
those tablespaces will be created by the server according to the
contents of the `tablespace_map` file that is included in the `base.tar`
file.

pg\_basebackup works with servers of the same or an older major version,
down to 9.1. However, WAL streaming mode (`-X
   stream`) only works with server version 9.3 and later, and tar format
(`--format=tar`) only works with server version 9.5 and later.

pg\_basebackup will preserve group permissions for data files if group
permissions are enabled on the source cluster.

Examples
========

To create a base backup of the server at `mydbserver` and store it in
the local directory `/usr/local/pgsql/data`:

    $ pg_basebackup -h mydbserver -D /usr/local/pgsql/data

To create a backup of the local server with one compressed tar file for
each tablespace, and store it in the directory `backup`, showing a
progress report while running:

    $ pg_basebackup -D backup -Ft -z -P

To create a backup of a single-tablespace local database and compress
this with bzip2:

    $ pg_basebackup -D - -Ft -X fetch | bzip2 > backup.tar.bz2

(This command will fail if there are multiple tablespaces in the
database.)

To create a backup of a local database where the tablespace in `/opt/ts`
is relocated to `./backup/ts`:

    $ pg_basebackup -D backup/data -T /opt/ts=$(pwd)/backup/ts

To create a backup of a local server with one tar file for each
tablespace compressed with gzip at level 9, stored in the directory
`backup`:

    $ pg_basebackup -D backup -Ft --compress=gzip:9

See Also
========
