---
title: "ALTER SYSTEM"
id: sql-altersystem
pg_version: "20devel"
---

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# ALTER SYSTEM — change a server configuration parameter

## Synopsis

```
ALTER SYSTEM SET configuration_parameter { TO | = } { value [, ...] | DEFAULT }

ALTER SYSTEM RESET configuration_parameter
ALTER SYSTEM RESET ALL
```

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## Description

`ALTER SYSTEM` is used for changing server configuration parameters across the entire database cluster. It can be more convenient than the traditional method of manually editing the `postgresql.conf` file. `ALTER SYSTEM` writes the given parameter setting to the `postgresql.auto.conf` file, which is read in addition to `postgresql.conf`. Setting a parameter to `DEFAULT`, or using the `RESET` variant, removes that configuration entry from the `postgresql.auto.conf` file. Use `RESET ALL` to remove all such configuration entries. 

Values set with `ALTER SYSTEM` will be effective after the next server configuration reload, or after the next server restart in the case of parameters that can only be changed at server start. A server configuration reload can be commanded by calling the SQL function `pg_reload_conf()`, running `pg_ctl reload`, or sending a SIGHUP signal to the main server process. 

Only superusers and users granted `ALTER SYSTEM` privilege on a parameter can change it using `ALTER SYSTEM`. Also, since this command acts directly on the file system and cannot be rolled back, it is not allowed inside a transaction block or function. 

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## Parameters

**`configuration_parameter`**

 Name of a settable configuration parameter. Available parameters are documented in [Chapter 19](runtime-config.md). **`value`**

 New value of the parameter. Values can be specified as string constants, identifiers, numbers, or comma-separated lists of these, as appropriate for the particular parameter. Values that are neither numbers nor valid identifiers must be quoted. If the parameter accepts a list of values, `NULL` can be written to specify an empty list. `DEFAULT` can be written to specify removing the parameter and its value from `postgresql.auto.conf`.  For some list-accepting parameters, quoted values will produce double-quoted output to preserve whitespace and commas; for others, double-quotes must be used inside single-quoted strings to get this effect. <a id="id-1.9.3.35.7"></a>

## Notes

This command can't be used to set [`data_directory` (`string`)](runtime-config-file-locations.md#guc-data-directory), [`allow_alter_system` (`boolean`)](runtime-config-compatible.md#guc-allow-alter-system), nor parameters that are not allowed in `postgresql.conf` (e.g., [preset options](runtime-config-preset.md)). 

See [Section 19.1](config-setting.md) for other ways to set the parameters. 

`ALTER SYSTEM` can be disabled by setting [`allow_alter_system` (`boolean`)](runtime-config-compatible.md#guc-allow-alter-system) to `off`, but this is not a security mechanism (as explained in detail in the documentation for this parameter). 

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## Examples

Set the `wal_level`: 
ALTER SYSTEM SET wal_level = replica;
 

Undo that, restoring whatever setting was effective in `postgresql.conf`: 
ALTER SYSTEM RESET wal_level;
 

Set the list of preloaded extension modules to be empty: 
ALTER SYSTEM SET shared_preload_libraries TO NULL;
 

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## Compatibility

The `ALTER SYSTEM` statement is a PostgreSQL extension. 

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## See Also

[SET](sql-set.md), [SHOW](sql-show.md)