> For the complete documentation index, see [llms.txt](https://docs.postgresql.tw/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.postgresql.tw/reference/sql-commands/sql-altersystem.md).

# ALTER SYSTEM

### ALTER SYSTEM

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
```

### 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.

### Parameters

*`configuration_parameter`* : Name of a settable configuration parameter. Available parameters are documented in [Chapter 19](/server-administration/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. `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.
```

### Notes

This command can't be used to set [data\_directory](/server-administration/runtime-config/runtime-config-file-locations.md#GUC-DATA-DIRECTORY), [allow\_alter\_system](/server-administration/runtime-config/runtime-config-compatible.md#GUC-ALLOW-ALTER-SYSTEM), nor parameters that are not allowed in `postgresql.conf` (e.g., [preset options](/server-administration/runtime-config/runtime-config-preset.md)).

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

`ALTER SYSTEM` can be disabled by setting [allow\_alter\_system](/server-administration/runtime-config/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).

### 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;
```

### Compatibility

The `ALTER SYSTEM` statement is a PostgreSQL extension.

### See Also

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

***

原文：[PostgreSQL 18.6 Documentation](https://www.postgresql.org/docs/18/sql-altersystem.html)（英文原文，待翻譯）


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