# 55P02 — cant_change_runtime_param

> Source-backed reference for PostgreSQL SQLSTATE 55P02.
---

# 55P02

## At a glance {#at-a-glance}

`55P02` means that PostgreSQL rejected a runtime-parameter change because the GUC context or lifecycle phase does not permit that operation. The same condition name covers restart-only, SIGHUP-only, backend-start, internal, and binary-upgrade guards.

<!-- BEGIN SQLSTATE FACTS: generated by scripts/generate.py; do not edit -->

| Field | Value |
| --- | --- |
| SQLSTATE | `55P02` |
| Condition | `cant_change_runtime_param` |
| Status | `active` |
| Known present by | `7.4` |
| Locked snapshots | `9.0.23, 9.1.24, 9.2.24, 9.3.25, 9.4.26, 9.5.25, 9.6.24, 10.23, 11.22, 12.22, 13.23, 14.24, 15.19, 16.15, 17.11, 18.6, 19beta3` |
| Macros | `ERRCODE_CANT_CHANGE_RUNTIME_PARAM` |
| Aliases | `—` |

<!-- source facts: data/errcodes/55P02.json -->
<!-- END SQLSTATE FACTS -->

## Meaning {#meaning}

`set_config_with_handle()` calls `ereport(elevel, ...)`, so the client-visible severity follows the caller: a SQL `SET` normally uses `ERROR`, while configuration-file/database-setting paths may use `LOG` or `WARNING`. The guard first checks the GUC context. Internal parameters cannot be changed by an ordinary caller; `PGC_POSTMASTER` parameters require a restart; `PGC_SIGHUP` parameters reject a session-only change with `parameter "%s" cannot be changed now`; and backend or superuser-backend parameters reject a late change with `parameter "%s" cannot be set after connection start`. The same restart message is also used when a reload would change a postmaster value, and `ALTER SYSTEM` rejects parameters that cannot be placed in its configuration file.

A separate `pg_upgrade_support.c` guard uses this SQLSTATE when a binary-upgrade helper is called while `IsBinaryUpgrade` is false. That path is an internal administrative precondition, not a regular `pg_settings.context` decision.

## Messages {#messages}

- Internal or configuration-file rejection: primary `parameter "%s" cannot be changed`; the `set_config_with_handle()` caller supplies the severity, while the `ALTER SYSTEM` guard uses ERROR.
- Restart-only parameter: primary `parameter "%s" cannot be changed without restarting the server`; the caller supplies the severity.
- SIGHUP-only parameter changed in a session: primary `parameter "%s" cannot be changed now`; the caller supplies the severity.
- Backend-start parameter changed after connection start: primary `parameter "%s" cannot be set after connection start`; the caller supplies the severity.
- Binary-upgrade helper outside binary-upgrade mode: primary `function can only be called when server is in binary upgrade mode`, ERROR.

## Diagnosis {#diagnosis}

Record the parameter name, exact primary message, source (`SET`, startup option, configuration reload, database/role setting, `ALTER SYSTEM`, or binary-upgrade helper), and the server phase. Check `pg_settings.context`, `pg_settings.pending_restart`, `pg_settings.source`, and `pg_settings.sourcefile`; a `postmaster` context points to restart, `sighup` to reload, and `backend` to a new session. A value-format problem has a different SQLSTATE and should not be diagnosed from `55P02`.

For a user `SET`, an `ERROR` aborts the current explicit transaction. For a configuration reload or background path, the same format may be logged or reported as a warning and does not imply a client transaction was aborted; use the reported severity and connection state.

## Response {#response}

Apply the change through the context named by `pg_settings`: use configuration and restart for restart-only values, reload SIGHUP values, pass backend-start values through a new connection, and leave internal or binary-upgrade-only parameters to their owning mechanism. In an explicit transaction, issue `ROLLBACK` or `ROLLBACK TO SAVEPOINT` after a failed SQL `SET` before sending further commands. In autocommit, correct the lifecycle or source first and retry the setting; do not blindly repeat the same rejected operation. Confirm the effective value after the transition.

## Versions {#versions}

The locked catalogue records this condition from 7.4; fixed source coverage is PostgreSQL 18.6. The `known present by` value is a catalogue boundary, not an exact implementation-introduction claim.

## Related {#related}

[`55P03`](../55p03/), [`57P03`](../57p03/), [`42501`](../42501/)

## Sources {#sources}

[src/backend/utils/misc/guc.c#L3407-3428](https://github.com/postgres/postgres/blob/724edf9bde9d356724ad384a2e196edc3c9f80f7/src/backend/utils/misc/guc.c#L3407)

[src/backend/utils/misc/guc.c#L3477-3512](https://github.com/postgres/postgres/blob/724edf9bde9d356724ad384a2e196edc3c9f80f7/src/backend/utils/misc/guc.c#L3477)

[src/backend/utils/misc/guc.c#L3550-3581](https://github.com/postgres/postgres/blob/724edf9bde9d356724ad384a2e196edc3c9f80f7/src/backend/utils/misc/guc.c#L3550)

[src/backend/utils/adt/pg_upgrade_support.c#L32-39](https://github.com/postgres/postgres/blob/724edf9bde9d356724ad384a2e196edc3c9f80f7/src/backend/utils/adt/pg_upgrade_support.c#L32)

[src/backend/utils/misc/guc.c#L4691-4694](https://github.com/postgres/postgres/blob/724edf9bde9d356724ad384a2e196edc3c9f80f7/src/backend/utils/misc/guc.c#L4691)

The structured [evidence record](../data/evidence/55p02.json) records fixed messages, caller-severity boundaries, and the source/runtime scope.