PG_BASEBACKUP(1) PostgreSQL 15.7 Documentation PG_BASEBACKUP(1)
NAME
pg_basebackup - take a base backup of a PostgreSQL cluster
SYNOPSIS
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
Section 26.3) and as the starting point for a log-shipping or
streaming-replication standby server (see Section 27.2).
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 pg_dump(1) 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 Section 22.2) or is a superuser, and
pg_hba.conf must permit the replication connection. The server must
also be configured with 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_basebackups 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 hot_standby, and configure its pg_hba.conf
appropriately). You will also need to enable 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.
Whenever pg_basebackup is taking a base backup, the server's
pg_stat_progress_basebackup view will report the progress of the
backup. See Section 28.4.5 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 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
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 Section 26.3.3).
-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 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.
pg_verifybackup(1) 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 pg_verifybackup(1). 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 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; 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 Section 34.15).
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 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 Section 55.4
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
pg_dump(1), Section 28.4.5
PostgreSQL 15.7 2024 PG_BASEBACKUP(1)
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