ExitPostmaster() says: /* * There is no known cause for a postmaster to become multithreaded after * startup. Recheck to account for the possibility of unknown causes. * This message uses LOG level, because an unclean shutdown at this point * would usually not look much different from a clean shutdown. */ if (pthread_is_threaded_np() != 0) ereport(LOG, (errcode(ERRCODE_INTERNAL_ERROR), errmsg_internal("postmaster became multithreaded"), errdetail("Please report this to <%s>.", PACKAGE_BUGREPORT)));
We now have a report[1] of a way to trigger this error message. It seems to boil down to "cause an error before PostmasterMain has reached its test of pthread_is_threaded_np()", for example $ # build with --enable-nls, using MacPorts' gettext package $ unset LANG $ postgres -D /foo postgres: could not access directory "/foo": No such file or directory Run initdb or pg_basebackup to initialize a PostgreSQL data directory. 2025-01-23 18:16:03.843 GMT [41524] LOG: postmaster became multithreaded 2025-01-23 18:16:03.843 GMT [41524] DETAIL: Please report this to <pgsql-b...@lists.postgresql.org>. I suggest therefore that we remove the "Please report a bug" bit and instead use the much more helpful hint appearing in PostmasterMain: errhint("Set the LC_ALL environment variable to a valid locale."))); An alternative idea (that maybe should also be done in PostmasterMain) is to report the HINT only #ifdef __darwin__ and on other platforms use the "Please report a bug" text. regards, tom lane [1] https://www.postgresql.org/message-id/18783-d1873b95a59b9103%40postgresql.org