<!--
doc/src/sgml/ref/pg_basebackup.sgml
PostgreSQL documentation
-->
<refentry id="app-pgbasebackup">
<indexterm zone="app-pgbasebackup">
<primary>pg_basebackup</primary>
</indexterm>
<refmeta>
<refentrytitle><application>pg_basebackup</application></refentrytitle>
<manvolnum>1</manvolnum>
<refmiscinfo>Application</refmiscinfo>
</refmeta>
<refnamediv>
<refname>pg_basebackup</refname>
<refpurpose>take a base backup of a <productname>PostgreSQL</productname> cluster</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>pg_basebackup</command>
<arg rep="repeat"><replaceable>option</replaceable></arg>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<application>pg_basebackup</application> is used to take a base backup of
a running <productname>PostgreSQL</productname> database cluster. The backup
is taken without affecting other clients of the database, and can be used
both for point-in-time recovery (see <xref linkend="continuous-archiving"/>)
and as the starting point for a log-shipping or streaming-replication standby
server (see <xref linkend="warm-standby"/>).
</para>
<para>
<application>pg_basebackup</application> can take a full or incremental
base backup of the database. When used to take a full backup, it makes an
exact copy of the database cluster's files. When used to take an incremental
backup, some files that would have been part of a full backup may be
replaced with incremental versions of the same files, containing only those
blocks that have been modified since the reference backup. An incremental
backup cannot be used directly; instead,
<xref linkend="app-pgcombinebackup"/> must first
be used to combine it with the previous backups upon which it depends.
See <xref linkend="backup-incremental-backup" /> for more information
about incremental backups, and <xref linkend="backup-pitr-recovery" />
for steps to recover from a backup.
</para>
<para>
In any mode, <application>pg_basebackup</application> makes 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
<xref linkend="app-pgdump"/> must be used.
</para>
<para>
The backup is made over a regular <productname>PostgreSQL</productname>
connection that uses the replication protocol. The connection must be made
with a user ID that has <literal>REPLICATION</literal> permissions
(see <xref linkend="role-attributes"/>) or is a superuser,
and <link linkend="auth-pg-hba-conf"><filename>pg_hba.conf</filename></link>
must permit the replication connection. The server must also be configured
with <xref linkend="guc-max-wal-senders"/> set high enough to provide at
least one walsender for the backup plus one for WAL streaming (if used).
</para>
<para>
There can be multiple <command>pg_basebackup</command>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.
</para>
<para>
<application>pg_basebackup</application> 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
<varname>max_wal_senders</varname> and <xref linkend="guc-hot-standby"/>,
and configure its <filename>pg_hba.conf</filename> appropriately).
You will also need to enable <xref linkend="guc-full-page-writes"/> on the primary.
</para>
<para>
Note that there are some limitations in taking a backup from a standby:
<itemizedlist>
<listitem>
<para>
The backup history file is not created in the database cluster backed up.
</para>
</listitem>
<listitem>
<para>
<application>pg_basebackup</application> cannot force the standby
to switch to a new WAL file at the end of backup.
When you are using <literal>-X none</literal>, if write activity on
the primary is low, <application>pg_basebackup</application> 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
<function>pg_switch_wal</function> on the primary in order to
trigger an immediate WAL file switch.
</para>
</listitem>
<listitem>
<para>
If the standby is promoted to be primary during backup, the backup fails.
</para>
</listitem>
<listitem>
<para>
All WAL records required for the backup must contain sufficient full-page writes,
which requires you to enable <varname>full_page_writes</varname> on the primary.
</para>
</listitem>
</itemizedlist>
</para>
<para>
Whenever <application>pg_basebackup</application> is taking a base
backup, the server's <structname>pg_stat_progress_basebackup</structname>
view will report the progress of the backup.
See <xref linkend="basebackup-progress-reporting"/> for details.
</para>
</refsect1>
<refsect1>
<title>Options</title>
<para>
The following command-line options control the location and format of the
output:
<variablelist>
<varlistentry>
<term><option>-D <replaceable class="parameter">directory</replaceable></option></term>
<term><option>--pgdata=<replaceable class="parameter">directory</replaceable></option></term>
<listitem>
<para>
Sets the target directory to write the output to.
<application>pg_basebackup</application> will create this directory
(and any missing parent directories) if it does not exist. If it
already exists, it must be empty.
</para>
<para>
When the backup is in tar format, the target directory may be
specified as <literal>-</literal> (dash), causing the tar file to be
written to <literal>stdout</literal>.
</para>
<para>
This option is required.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-F <replaceable class="parameter">format</replaceable></option></term>
<term><option>--format=<replaceable class="parameter">format</replaceable></option></term>
<listitem>
<para>
Selects the format for the output. <replaceable>format</replaceable>
can be one of the following:
<variablelist>
<varlistentry>
<term><literal>p</literal></term>
<term><literal>plain</literal></term>
<listitem>
<para>
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 <option>--tablespace-mapping</option> to change that.)
</para>
<para>
This is the default format.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>t</literal></term>
<term><literal>tar</literal></term>
<listitem>
<para>
Write the output as tar files in the target directory. The main
data directory's contents will be written to a file named
<filename>base.tar</filename>, and each other tablespace will be
written to a separate tar file named after that tablespace's OID.
</para>
<para>
If the target directory is specified as <literal>-</literal>
(dash), the tar contents will be written to
standard output, suitable for piping to (for example)
<productname>gzip</productname>. This is only allowed if
the cluster has no additional tablespaces and WAL
streaming is not used.
</para>
</listitem>
</varlistentry>
</variablelist></para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-i <replaceable class="parameter">old_manifest_file</replaceable></option></term>
<term><option>--incremental=<replaceable class="parameter">old_manifest_file</replaceable></option></term>
<listitem>
<para>
Performs an <link linkend="backup-incremental-backup">incremental
backup</link>. The backup manifest for the reference
backup must be provided, and will be uploaded to the server, which will
respond by sending the requested incremental backup.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-R</option></term>
<term><option>--write-recovery-conf</option></term>
<listitem>
<para>
Creates a
<link linkend="file-standby-signal"><filename>standby.signal</filename></link>
<indexterm><primary><filename>standby.signal</filename></primary><secondary>pg_basebackup --write-recovery-conf</secondary></indexterm>
file and appends
connection settings to the <filename>postgresql.auto.conf</filename>
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.
</para>
<para>
The <filename>postgresql.auto.conf</filename> file will record the connection
settings and, if specified, the replication slot
that <application>pg_basebackup</application> is using, so that
streaming replication and <link linkend="logicaldecoding-replication-slots-synchronization">
logical replication slot synchronization</link> will use the same
settings later on. The dbname will be recorded only if the dbname was
specified explicitly in the connection string or <link linkend="libpq-envars">
environment variable</link>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-t <replaceable class="parameter">target</replaceable></option></term>
<term><option>--target=<replaceable class="parameter">target</replaceable></option></term>
<listitem>
<para>
Instructs the server where to place the base backup. The default target
is <literal>client</literal>, which specifies that the backup should
be sent to the machine where <application>pg_basebackup</application>
is running. If the target is instead set to
<literal>server:/some/path</literal>, the backup will be stored on
the machine where the server is running in the
<literal>/some/path</literal> directory. Storing a backup on the
server requires superuser privileges or having privileges of the
<literal>pg_write_server_files</literal> role. If the target is set to
<literal>blackhole</literal>, 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.
</para>
<para>
Since WAL streaming is implemented by
<application>pg_basebackup</application> rather than by the server,
this option cannot be used together with <literal>-Xstream</literal>.
Since that is the default, when this option is specified, you must also
specify either <literal>-Xfetch</literal> or <literal>-Xnone</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-T <replaceable class="parameter">olddir</replaceable>=<replaceable class="parameter">newdir</replaceable></option></term>
<term><option>--tablespace-mapping=<replaceable class="parameter">olddir</replaceable>=<replaceable class="parameter">newdir</replaceable></option></term>
<listitem>
<para>
Relocates the tablespace in directory <replaceable>olddir</replaceable>
to <replaceable>newdir</replaceable> during the backup. To be
effective, <replaceable>olddir</replaceable> 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 <replaceable>olddir</replaceable> on the source server.)
Meanwhile <replaceable>newdir</replaceable> is a directory in the
receiving host's filesystem. As with the main target directory,
<replaceable>newdir</replaceable> need not exist already, but if
it does exist it must be empty.
Both <replaceable>olddir</replaceable>
and <replaceable>newdir</replaceable> must be absolute paths. If
either path needs to contain an equal sign (<literal>=</literal>),
precede that with a backslash. This option can be specified multiple
times for multiple tablespaces.
</para>
<para>
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.
</para>
<para>
Currently, this option only works with plain output format; it is
ignored if tar format is selected.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--waldir=<replaceable class="parameter">waldir</replaceable></option></term>
<listitem>
<para>
Sets the directory to write WAL (write-ahead log) files to.
By default WAL files will be placed in
the <filename>pg_wal</filename> subdirectory of the target
directory, but this option can be used to place them elsewhere.
<replaceable>waldir</replaceable> must be an absolute path.
As with the main target directory,
<replaceable>waldir</replaceable> 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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-X <replaceable class="parameter">method</replaceable></option></term>
<term><option>--wal-method=<replaceable class="parameter">method</replaceable></option></term>
<listitem>
<para>
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 <literal>none</literal> is specified,
it is possible to start a postmaster in the target
directory without the need to consult the WAL archive, thus
making the output a completely standalone backup.
</para>
<para>
The following <replaceable>method</replaceable>s for collecting the
write-ahead logs are supported:
<variablelist>
<varlistentry>
<term><literal>n</literal></term>
<term><literal>none</literal></term>
<listitem>
<para>
Don't include write-ahead logs in the backup.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>f</literal></term>
<term><literal>fetch</literal></term>
<listitem>
<para>
The write-ahead log files are collected at the end of the backup.
Therefore, it is necessary for the source server's
<xref linkend="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.
</para>
<para>
When tar format is used, the write-ahead log files will be
included in the <filename>base.tar</filename> file.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>s</literal></term>
<term><literal>stream</literal></term>
<listitem>
<para>
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.
</para>
<para>
When tar format is used, the write-ahead log files will be
written to a separate file named <filename>pg_wal.tar</filename>
(if the server is a version earlier than 10, the file will be named
<filename>pg_xlog.tar</filename>).
</para>
<para>
This value is the default.
</para>
</listitem>
</varlistentry>
</variablelist></para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-z</option></term>
<term><option>--gzip</option></term>
<listitem>
<para>
Enables gzip compression of tar file output, with the default
compression level. Compression is only available when using
the tar format, and the suffix <filename>.gz</filename> will
automatically be added to all tar filenames.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-Z <replaceable class="parameter">level</replaceable></option></term>
<term><option>-Z [{client|server}-]<replaceable class="parameter">method</replaceable>[:<replaceable>detail</replaceable>]</option></term>
<term><option>--compress=<replaceable class="parameter">level</replaceable></option></term>
<term><option>--compress=[{client|server}-]<replaceable class="parameter">method</replaceable>[:<replaceable>detail</replaceable>]</option></term>
<listitem>
<para>
Requests compression of the backup. If <literal>client</literal> or
<literal>server</literal> 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 <literal>client</literal> except when
<literal>--target</literal> is used. In that case, the backup is not
being sent to the client, so only server compression is sensible.
When <literal>-Xstream</literal>, 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 <literal>-Xfetch</literal>.
</para>
<para>
The compression method can be set to <literal>gzip</literal>,
<literal>lz4</literal>, <literal>zstd</literal>,
<literal>none</literal> for no compression or an integer (no
compression if 0, <literal>gzip</literal> if greater than 0).
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
<replaceable>keyword</replaceable> or
<replaceable>keyword=value</replaceable>.
Currently, the supported keywords are <literal>level</literal>,
<literal>long</literal>, and <literal>workers</literal>.
The detail string cannot be used when the compression method
is specified as a plain integer.
</para>
<para>
If no compression level is specified, the default compression level
will be used. If only a level is specified without mentioning an
algorithm, <literal>gzip</literal> compression will be used if the
level is greater than 0, and no compression will be used if the level
is 0.
</para>
<para>
When the tar format is used with <literal>gzip</literal>,
<literal>lz4</literal>, or <literal>zstd</literal>, the suffix
<filename>.gz</filename>, <filename>.lz4</filename>, or
<filename>.zst</filename>, 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.
</para>
<para>
When this option is used in combination with
<literal>-Xstream</literal>, <literal>pg_wal.tar</literal> will
be compressed using <literal>gzip</literal> 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.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
The following command-line options control the generation of the
backup and the invocation of the program:
<variablelist>
<varlistentry>
<term><option>-c {fast|spread}</option></term>
<term><option>--checkpoint={fast|spread}</option></term>
<listitem>
<para>
Sets checkpoint mode to fast (immediate) or spread (the default)
(see <xref linkend="backup-lowlevel-base-backup"/>).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-C</option></term>
<term><option>--create-slot</option></term>
<listitem>
<para>
Specifies that the replication slot named by the
<literal>--slot</literal> option should be created before starting
the backup. An error is raised if the slot already exists.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-l <replaceable class="parameter">label</replaceable></option></term>
<term><option>--label=<replaceable class="parameter">label</replaceable></option></term>
<listitem>
<para>
Sets the label for the backup. If none is specified, a default value of
<quote><literal>pg_basebackup base backup</literal></quote> will be used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-n</option></term>
<term><option>--no-clean</option></term>
<listitem>
<para>
By default, when <command>pg_basebackup</command> 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.
</para>
<para>
Note that tablespace directories are not cleaned up either way.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-N</option></term>
<term><option>--no-sync</option></term>
<listitem>
<para>
By default, <command>pg_basebackup</command> will wait for all files
to be written safely to disk. This option causes
<command>pg_basebackup</command> 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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-P</option></term>
<term><option>--progress</option></term>
<listitem>
<para>
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
<literal>100%</literal>. 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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-r <replaceable class="parameter">rate</replaceable></option></term>
<term><option>--max-rate=<replaceable class="parameter">rate</replaceable></option></term>
<listitem>
<para>
Sets the maximum transfer rate at which data is collected from the
source server. This can be useful to limit the impact
of <application>pg_basebackup</application> on the server. Values
are in kilobytes per second. Use a suffix of <literal>M</literal>
to indicate megabytes per second. A suffix of <literal>k</literal>
is also accepted, and has no effect. Valid values are between 32
kilobytes per second and 1024 megabytes per second.
</para>
<para>
This option always affects transfer of the data directory. Transfer of
WAL files is only affected if the collection method
is <literal>fetch</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-S <replaceable>slotname</replaceable></option></term>
<term><option>--slot=<replaceable class="parameter">slotname</replaceable></option></term>
<listitem>
<para>
This option can only be used together with <literal>-X
stream</literal>. 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
<xref linkend="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.
</para>
<para>
The specified replication slot has to exist unless the
option <option>-C</option> is also used.
</para>
<para>
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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--sync-method=<replaceable class="parameter">method</replaceable></option></term>
<listitem>
<para>
When set to <literal>fsync</literal>, which is the default,
<command>pg_basebackup</command> will recursively open and synchronize
all files in the backup directory. When the plain format is used, the
search for files will follow symbolic links for the WAL directory and
each configured tablespace.
</para>
<para>
On Linux, <literal>syncfs</literal> may be used instead to ask the
operating system to synchronize the whole file system that contains the
backup directory. When the plain format is used,
<command>pg_basebackup</command> will also synchronize the file systems
that contain the WAL files and each tablespace. See
<xref linkend="guc-recovery-init-sync-method"/> for information about
the caveats to be aware of when using <literal>syncfs</literal>.
</para>
<para>
This option has no effect when <option>--no-sync</option> is used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-v</option></term>
<term><option>--verbose</option></term>
<listitem>
<para>
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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--manifest-checksums=<replaceable class="parameter">algorithm</replaceable></option></term>
<listitem>
<para>
Specifies the checksum algorithm that should be applied to each file
included in the backup manifest. Currently, the available
algorithms are <literal>NONE</literal>, <literal>CRC32C</literal>,
<literal>SHA224</literal>, <literal>SHA256</literal>,
<literal>SHA384</literal>, and <literal>SHA512</literal>.
The default is <literal>CRC32C</literal>.
</para>
<para>
If <literal>NONE</literal> 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 <literal>SHA256</literal>
checksum of its own contents. The <literal>SHA</literal> algorithms
are significantly more CPU-intensive than <literal>CRC32C</literal>,
so selecting one of them may increase the time required to complete
the backup.
</para>
<para>
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 CRC-32C 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.
</para>
<para>
<xref linkend="app-pgverifybackup"/> can be used to check the
integrity of a backup against the backup manifest.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--manifest-force-encode</option></term>
<listitem>
<para>
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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--no-estimate-size</option></term>
<listitem>
<para>
Prevents the server from estimating the total
amount of backup data that will be streamed, resulting in the
<structfield>backup_total</structfield> column in the
<structname>pg_stat_progress_basebackup</structname> view
always being <literal>NULL</literal>.
</para>
<para>
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.
</para>
<para>
This option is not allowed when using <option>--progress</option>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--no-manifest</option></term>
<listitem>
<para>
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 <xref linkend="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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--no-slot</option></term>
<listitem>
<para>
Prevents the creation of a temporary replication slot
for the backup.
</para>
<para>
By default, if log streaming is selected but no slot name is given
with the <option>-S</option> option, then a temporary replication
slot is created (if supported by the source server).
</para>
<para>
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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--no-verify-checksums</option></term>
<listitem>
<para>
Disables verification of checksums, if they are enabled on the server
the base backup is taken from.
</para>
<para>
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 <option>--no-clean</option> option
had been used. Checksum verification failures will also be reported
in the <link linkend="monitoring-pg-stat-database-view">
<structname>pg_stat_database</structname></link> view.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
The following command-line options control the connection to the source
server:
<variablelist>
<varlistentry>
<term><option>-d <replaceable class="parameter">connstr</replaceable></option></term>
<term><option>--dbname=<replaceable class="parameter">connstr</replaceable></option></term>
<listitem>
<para>
Specifies parameters used to connect to the server, as a <link
linkend="libpq-connstring">connection string</link>; these
will override any conflicting command line options.
</para>
<para>
This option is called <literal>--dbname</literal> for consistency with other
client applications, but because <application>pg_basebackup</application>
doesn't connect to any particular database in the cluster, any database
name included in the connection string will be ignored by the server.
However, a database name supplied that way overrides the default
database name (<literal>replication</literal>) for purposes of
looking up the replication connection's password
in <filename>~/.pgpass</filename>. Similarly, middleware or proxies
used in connecting to <productname>PostgreSQL</productname> might
utilize the name for purposes such as connection routing. The
database name can also be used
by <link linkend="logicaldecoding-replication-slots-synchronization">
logical replication slot synchronization</link>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-h <replaceable class="parameter">host</replaceable></option></term>
<term><option>--host=<replaceable class="parameter">host</replaceable></option></term>
<listitem>
<para>
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 <envar>PGHOST</envar> environment variable, if set,
else a Unix domain socket connection is attempted.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-p <replaceable class="parameter">port</replaceable></option></term>
<term><option>--port=<replaceable class="parameter">port</replaceable></option></term>
<listitem>
<para>
Specifies the TCP port or local Unix domain socket file
extension on which the server is listening for connections.
Defaults to the <envar>PGPORT</envar> environment variable, if
set, or a compiled-in default.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-s <replaceable class="parameter">interval</replaceable></option></term>
<term><option>--status-interval=<replaceable class="parameter">interval</replaceable></option></term>
<listitem>
<para>
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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-U <replaceable>username</replaceable></option></term>
<term><option>--username=<replaceable class="parameter">username</replaceable></option></term>
<listitem>
<para>
Specifies the user name to connect as.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-w</option></term>
<term><option>--no-password</option></term>
<listitem>
<para>
Prevents issuing a password prompt. If the server requires
password authentication and a password is not available by
other means such as a <filename>.pgpass</filename> 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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-W</option></term>
<term><option>--password</option></term>
<listitem>
<para>
Forces <application>pg_basebackup</application> to prompt for a
password before connecting to the source server.
</para>
<para>
This option is never essential, since
<application>pg_basebackup</application> will automatically prompt
for a password if the server demands password authentication.
However, <application>pg_basebackup</application> will waste a
connection attempt finding out that the server wants a password.
In some cases it is worth typing <option>-W</option> to avoid the extra
connection attempt.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
Other options are also available:
<variablelist>
<varlistentry>
<term><option>-V</option></term>
<term><option>--version</option></term>
<listitem>
<para>
Prints the <application>pg_basebackup</application> version and exits.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-?</option></term>
<term><option>--help</option></term>
<listitem>
<para>
Shows help about <application>pg_basebackup</application> command line
arguments, and exits.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1>
<title>Environment</title>
<para>
This utility, like most other <productname>PostgreSQL</productname> utilities,
uses the environment variables supported by <application>libpq</application>
(see <xref linkend="libpq-envars"/>).
</para>
<para>
The environment variable <envar>PG_COLOR</envar> specifies whether to use
color in diagnostic messages. Possible values are
<literal>always</literal>, <literal>auto</literal> and
<literal>never</literal>.
</para>
</refsect1>
<refsect1>
<title>Notes</title>
<para>
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
<literal>--checkpoint=fast</literal> is not used), during
which <application>pg_basebackup</application> will appear to be idle.
</para>
<para>
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 and operating system files. 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 <xref linkend="protocol-replication"/> for the precise details.
</para>
<para>
In plain format, tablespaces will be backed up to the same path
they have on the source server, unless the
option <literal>--tablespace-mapping</literal> 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.
</para>
<para>
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 <filename>tablespace_map</filename> file that is
included in the <filename>base.tar</filename> file.
</para>
<para>
<application>pg_basebackup</application> works with servers of the same
or older major version, down to 9.1. However, WAL streaming mode (<literal>-X
stream</literal>) only works with server version 9.3 and later, the tar format
(<literal>--format=tar</literal>) only works with server version 9.5
and later, and incremental backup (<literal>--incremental</literal>) only works
with server version 17 and later.
</para>
<para>
<application>pg_basebackup</application> will preserve group permissions
for data files if group permissions are enabled on the source cluster.
</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
To create a base backup of the server at <literal>mydbserver</literal>
and store it in the local directory
<filename>/usr/local/pgsql/data</filename>:
<screen>
<prompt>$</prompt> <userinput>pg_basebackup -h mydbserver -D /usr/local/pgsql/data</userinput>
</screen>
</para>
<para>
To create a backup of the local server with one compressed
tar file for each tablespace, and store it in the directory
<filename>backup</filename>, showing a progress report while running:
<screen>
<prompt>$</prompt> <userinput>pg_basebackup -D backup -Ft -z -P</userinput>
</screen>
</para>
<para>
To create a backup of a single-tablespace local database and compress
this with <productname>bzip2</productname>:
<screen>
<prompt>$</prompt> <userinput>pg_basebackup -D - -Ft -X fetch | bzip2 &gt; backup.tar.bz2</userinput>
</screen>
(This command will fail if there are multiple tablespaces in the
database.)
</para>
<para>
To create a backup of a local database where the tablespace in
<filename>/opt/ts</filename> is relocated
to <filename>./backup/ts</filename>:
<screen>
<prompt>$</prompt> <userinput>pg_basebackup -D backup/data -T /opt/ts=$(pwd)/backup/ts</userinput>
</screen></para>
<para>
To create a backup of the local server with one tar file for each tablespace
compressed with <application>gzip</application> at level 9, stored in the
directory <filename>backup</filename>:
<screen>
<prompt>$</prompt> <userinput>pg_basebackup -D backup -Ft --compress=gzip:9</userinput>
</screen></para>
</refsect1>
<refsect1>
<title>See Also</title>
<simplelist type="inline">
<member><xref linkend="app-pgdump"/></member>
<member><xref linkend="basebackup-progress-reporting"/></member>
</simplelist>
</refsect1>
</refentry>