How do I locate my Postgres data directory while the server is down?
Check  /usr/local/var/postgres

See also answers for Mac in How do I find PostgreSQL&#39;s data directory?.

A Linux PGDATA directory looks like:

bash-4.2$ ls -al $PGDATA
total 72
drwx------. 20 postgres postgres  4096 Apr  8 16:44 .
drwx------.  4 postgres postgres    31 Feb 11 23:07 ..
drwx------.  7 postgres postgres    62 Apr  7 21:27 base
-rw-------.  1 postgres postgres    30 Apr  8 16:44 current_logfiles
drwx------.  2 postgres postgres  4096 Apr  8 17:47 global
drwx------.  2 postgres postgres  4096 Apr  7 08:07 log
drwx------.  2 postgres postgres     6 Feb 13 09:21 pg_commit_ts
drwx------.  2 postgres postgres     6 Feb 13 09:21 pg_dynshmem
-rw-------.  1 postgres postgres  4513 Feb 13 09:21 pg_hba.conf
-rw-------.  1 postgres postgres  1636 Feb 13 09:21 pg_ident.conf
drwx------.  4 postgres postgres    65 Apr  8 17:49 pg_logical
drwx------.  4 postgres postgres    34 Feb 13 09:21 pg_multixact
drwx------.  2 postgres postgres    17 Apr  8 16:44 pg_notify
drwx------.  2 postgres postgres     6 Feb 13 09:21 pg_replslot
drwx------.  2 postgres postgres     6 Feb 13 09:21 pg_serial
drwx------.  2 postgres postgres     6 Feb 13 09:21 pg_snapshots
drwx------.  2 postgres postgres     6 Apr  8 16:44 pg_stat
drwx------.  2 postgres postgres  4096 Apr  8 17:49 pg_stat_tmp
drwx------.  2 postgres postgres    17 Feb 13 09:21 pg_subtrans
drwx------.  2 postgres postgres     6 Feb 13 09:21 pg_tblspc
drwx------.  2 postgres postgres     6 Feb 13 09:21 pg_twophase
-rw-------.  1 postgres postgres     3 Feb 13 09:21 PG_VERSION
drwx------.  3 postgres postgres    89 Mar 21 15:02 pg_wal
drwx------.  2 postgres postgres    17 Feb 13 09:21 pg_xact
-rw-------.  1 postgres postgres    88 Feb 13 09:21 postgresql.auto.conf
-rw-------.  1 postgres postgres 24005 Feb 13 09:21 postgresql.conf
-rw-------.  1 postgres postgres    27 Apr  8 16:44 postmaster.opts
-rw-------.  1 postgres postgres   104 Apr  8 16:44 postmaster.pid
-bash-4.2$