18.3. Starting the Database Server

Before anyone can access the database, you must start the database server. The database server program is called postgres. The postgres program must know where to find the data it is supposed to use. This is done with the -D option. Thus, the simplest way to start the server is:

$ postgres -D /usr/local/pgsql/data

which will leave the server running in the foreground. This must be done while logged into the PostgreSQL user account. Without -D, the server will try to use the data directory named by the environment variable PGDATA. If that variable is not provided either, it will fail.

Normally it is better to start postgres in the background. For this, use the usual Unix shell syntax:

$ postgres -D /usr/local/pgsql/data >logfile 2>&1 &

It is important to store the server's stdout and stderr output somewhere, as shown above. It will help for auditing purposes and to diagnose problems. (See Section 24.3 for a more thorough discussion of log file handling.)

The postgres program also takes a number of other command-line options. For more information, see the postgres reference page and Chapter 19 below.

This shell syntax can get tedious quickly. Therefore the wrapper program pg_ctl is provided to simplify some tasks. For example:

pg_ctl start -l logfile

will start the server in the background and put the output into the named log file. The -D option has the same meaning here as for postgres. pg_ctl is also capable of stopping the server.

Normally, you will want to start the database server when the computer boots. Autostart scripts are operating-system-specific. There are a few distributed with PostgreSQL in the contrib/start-scripts directory. Installing one will require root privileges.

Different systems have different conventions for starting up daemons at boot time. Many systems have a file /etc/rc.local or /etc/rc.d/rc.local. Others use init.d or rc.d directories. Whatever you do, the server must be run by the PostgreSQL user account and not by root or any other user. Therefore you probably should form your commands using su postgres -c '...'. For example:

su postgres -c 'pg_ctl start -D /usr/local/pgsql/data -l serverlog'

Here are a few more operating-system-specific suggestions. (In each case be sure to use the proper installation directory and user name where we show generic values.)

• For FreeBSD, look at the file contrib/start-scripts/freebsd in the PostgreSQL source distribution.

• On OpenBSD, add the following lines to the file /etc/rc.local:

  if [ -x /usr/local/pgsql/bin/pg_ctl -a -x /usr/local/pgsql/bin/postgres ]; then
      su -l postgres -c '/usr/local/pgsql/bin/pg_ctl start -s -l /var/postgresql/log -D /usr/local/pgsql/data'
      echo -n ' postgresql'
  fi

• On Linux systems either add

  /usr/local/pgsql/bin/pg_ctl start -l logfile -D /usr/local/pgsql/data

  to /etc/rc.d/rc.local or /etc/rc.local or look at the file contrib/start-scripts/linux in the PostgreSQL source distribution.

  When using systemd, you can use the following service unit file (e.g., at /etc/systemd/system/postgresql.service):

  [Unit]
  Description=PostgreSQL database server
  Documentation=man:postgres(1)
  
  [Service]
  Type=notify
  User=postgres
  ExecStart=/usr/local/pgsql/bin/postgres -D /usr/local/pgsql/data
  ExecReload=/bin/kill -HUP $MAINPID
  KillMode=mixed
  KillSignal=SIGINT
  TimeoutSec=0
  
  [Install]
  WantedBy=multi-user.target

  Using Type=notify requires that the server binary was built with configure --with-systemd.

  Consider carefully the timeout setting. systemd has a default timeout of 90 seconds as of this writing and will kill a process that does not notify readiness within that time. But a PostgreSQL server that might have to perform crash recovery at startup could take much longer to become ready. The suggested value of 0 disables the timeout logic.

• On NetBSD, use either the FreeBSD or Linux start scripts, depending on preference.

• On Solaris, create a file called /etc/init.d/postgresql that contains the following line:

  su - postgres -c "/usr/local/pgsql/bin/pg_ctl start -l logfile -D /usr/local/pgsql/data"

  Then, create a symbolic link to it in /etc/rc3.d as S99postgresql.

While the server is running, its PID is stored in the file postmaster.pid in the data directory. This is used to prevent multiple server instances from running in the same data directory and can also be used for shutting down the server.

LOG:  could not bind IPv4 socket: Address already in use
HINT:  Is another postmaster already running on port 5432? If not, wait a few seconds and retry.
FATAL:  could not create TCP/IP listen socket

$ postgres -p 666
LOG:  could not bind IPv4 socket: Permission denied
HINT:  Is another postmaster already running on port 666? If not, wait a few seconds and retry.
FATAL:  could not create TCP/IP listen socket

FATAL:  could not create shared memory segment: Invalid argument
DETAIL:  Failed system call was shmget(key=5440001, size=4011376640, 03600).

FATAL:  could not create semaphores: No space left on device
DETAIL:  Failed system call was semget(5440126, 17, 03600).

psql: could not connect to server: Connection refused
        Is the server running on host "server.joe.com" and accepting
        TCP/IP connections on port 5432?

psql: could not connect to server: No such file or directory
        Is the server running locally and accepting
        connections on Unix domain socket "/tmp/.s.PGSQL.5432"?