external_pid_file

Definition PG 18 manual

Specifies the name of an additional process-ID (PID) file that the server should create for use by server administration programs. This parameter can only be set at server start.

How it works

Writes the postmaster PID to the specified file. The value is fixed when the server starts, so changing it requires a restart.

At startup PostgreSQL writes the postmaster PID to this additional path for external service tooling. postmaster.pid in the data directory remains authoritative for server internals, and the external file must not be used as the sole proof that a process is the intended cluster.

Monitor and change external_pid_file together with allow_alter_system, config_file, data_directory. Validate on the relevant server role and real workload, then use its postmaster context to choose session change, reload, or restart; a historical boot default is not the current effective value.

Operational considerations

Missing directory traversal, read, or write permission for the service account.

Confusing restart requirements for a path with reload behavior of the selected file contents.

Omitting the path on a failover node or from backup inventory.

Using a relative path that depends on an unstable working directory.

Workload guidance

OLAP: Follow the OLTP rule, and for separate mounts also verify boot ordering, backup coverage, and path consistency on failover nodes.

OLTP: external_pid_file is deployment topology, not workload tuning. Use an absolute path, least privilege, and atomic configuration rollout; verify access as the postgres service account before restart/reload.

SMALL: The default co-located layout is simplest. Split paths only for a concrete backup, packaging, or permission-isolation benefit.