In an event of a DB crash or an unclean shutdown (host node failure), sometimes Postgres cannot find a valid checkpoint to start. The logs look like:
2021-02-16 04:09:44.977 UTC  LOG: database system was shut down at 2021-02-16 03:50:02 UTC 2021-02-16 04:09:44.978 UTC  LOG: record with incorrect prev-link 1DF0000/7BB0000 at 0/D786C2B0 2021-02-16 04:09:44.978 UTC  LOG: invalid primary checkpoint record 2021-02-16 04:09:44.978 UTC  PANIC: could not locate a valid checkpoint record 2021-02-16 04:09:45.252 UTC  LOG: startup process (PID 26) was terminated by signal 6: Aborted 2021-02-16 04:09:45.252 UTC  LOG: aborting startup due to startup process failure 2021-02-16 04:09:45.254 UTC  LOG: database system is shut down
The line to notice here is:
2021-02-16 04:09:44.978 UTC  PANIC: could not locate a valid checkpoint record
In such a scenario, perform a WAL Log Reset with
Quoting from the docs:
pg_resetwal clears the write-ahead log (WAL) and optionally resets some other control information stored in the pg_control file. This function is sometimes needed if these files have become corrupted. It should be used only as a last resort, when the server will not start due to such corruption.
$ su postgres $ pg_resetwal /var/lib/postgresql/data
Postgres should initialise now. But as the docs clarify further:
After running this command, it should be possible to start the server, but bear in mind that the database might contain inconsistent data due to partially-committed transactions. You should immediately dump your data, run initdb, and reload. After reload, check for inconsistencies and repair as needed.