Процессы операционной системы 

postgres$ ps -o pid,command --ppid `head -n 1 $PGDATA/postmaster.pid`

  PID COMMAND
11442 postgres: 9.6/main: checkpointer process   
11443 postgres: 9.6/main: writer process   
11444 postgres: 9.6/main: wal writer process   
11445 postgres: 9.6/main: autovacuum launcher process   
11446 postgres: 9.6/main: stats collector process   
23142 postgres: 9.6/main: autovacuum worker process   plpgsql_exceptions

К процессам, обслуживающим буферный кэш и журнал, можно отнести:

Остановка в режиме fast 

postgres$ rm /var/log/postgresql/postgresql-9.6-main.log

student$ sudo pg_ctlcluster 9.6 main restart

Журнал сообщений сервера: 

postgres$ cat /var/log/postgresql/postgresql-9.6-main.log

2017-09-01 15:53:37 MSK [26546-1] LOG:  database system was shut down at 2017-09-01 15:53:36 MSK
2017-09-01 15:53:37 MSK [26546-2] LOG:  MultiXact member wraparound protections are now enabled
2017-09-01 15:53:37 MSK [26545-1] LOG:  database system is ready to accept connections
2017-09-01 15:53:37 MSK [26550-1] LOG:  autovacuum launcher started
2017-09-01 15:53:38 MSK [26552-1] [unknown]@[unknown] LOG:  incomplete startup packet

Остановка в режиме immediate 

postgres$ rm /var/log/postgresql/postgresql-9.6-main.log

student$ sudo pg_ctlcluster 9.6 main stop -m immediate --skip-systemctl-redirect

student$ sudo pg_ctlcluster 9.6 main restart

Журнал сообщений сервера: 

postgres$ cat /var/log/postgresql/postgresql-9.6-main.log

2017-09-01 15:53:40 MSK [26624-1] LOG:  database system was interrupted; last known up at 2017-09-01 15:53:37 MSK
2017-09-01 15:53:40 MSK [26625-1] [unknown]@[unknown] LOG:  incomplete startup packet
2017-09-01 15:53:41 MSK [26628-1] postgres@postgres FATAL:  the database system is starting up
2017-09-01 15:53:41 MSK [26624-2] LOG:  database system was not properly shut down; automatic recovery in progress
2017-09-01 15:53:41 MSK [26624-3] LOG:  invalid record length at F/992EB1CC: wanted 24, got 0
2017-09-01 15:53:41 MSK [26624-4] LOG:  redo is not required
2017-09-01 15:53:41 MSK [26624-5] LOG:  MultiXact member wraparound protections are now enabled
2017-09-01 15:53:41 MSK [26623-1] LOG:  database system is ready to accept connections
2017-09-01 15:53:41 MSK [26632-1] LOG:  autovacuum launcher started

Перед тем, как начать принимать соединения, СУБД выполнила восстановление (automatic recovery in progress).