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
/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) After=network-online.target Wants=network-online.target [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=infinity [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 report
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 infinity 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.
There are several common reasons the server might fail to start. Check the server's log file, or start it by hand (without redirecting standard output or standard error) and see what error messages appear. Below we explain some of the most common error messages in more detail.
LOG: could not bind IPv4 address "127.0.0.1": 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 any TCP/IP sockets
This usually means just what it suggests: you tried to start
another server on the same port where one is already running.
However, if the kernel error message is not Address
already in use or some variant of that, there might
be a different problem. For example, trying to start a server
on a reserved port number might draw something like:
$ postgres -p 666
LOG: could not bind IPv4 address "127.0.0.1": Permission denied
HINT: Is another postmaster already running on port 666? If not, wait a few seconds and retry.
FATAL: could not create any TCP/IP sockets
A message like:
FATAL: could not create shared memory segment: Invalid argument DETAIL: Failed system call was shmget(key=5440001, size=4011376640, 03600).
probably means your kernel's limit on the size of shared memory is smaller than the work area PostgreSQL is trying to create (4011376640 bytes in this example). Or it could mean that you do not have System-V-style shared memory support configured into your kernel at all. As a temporary workaround, you can try starting the server with a smaller-than-normal number of buffers (shared_buffers). You will eventually want to reconfigure your kernel to increase the allowed shared memory size. You might also see this message when trying to start multiple servers on the same machine, if their total space requested exceeds the kernel limit.
An error like:
FATAL: could not create semaphores: No space left on device DETAIL: Failed system call was semget(5440126, 17, 03600).
does not mean you've run out of disk space. It means your kernel's limit on the number of System V semaphores is smaller than the number PostgreSQL wants to create. As above, you might be able to work around the problem by starting the server with a reduced number of allowed connections (max_connections), but you'll eventually want to increase the kernel limit.
If you get an “illegal system call” error, it is likely that shared memory or semaphores are not supported in your kernel at all. In that case your only option is to reconfigure the kernel to enable these features.
Details about configuring System V IPC facilities are given in Section 18.4.1.
Although the error conditions possible on the client side are quite varied and application-dependent, a few of them might be directly related to how the server was started. Conditions other than those shown below should be documented with the respective client application.
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?
This is the generic “I couldn't find a server to talk to” failure. It looks like the above when TCP/IP communication is attempted. A common mistake is to forget to configure the server to allow TCP/IP connections.
Alternatively, you'll get this when attempting Unix-domain socket communication to a local server:
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"?
The last line is useful in verifying that the client is trying to
connect to the right place. If there is in fact no server
running there, the kernel error message will typically be either
Connection refused or
No such file or directory, as
illustrated. (It is important to realize that
Connection refused in this context
does not mean that the server got your
connection request and rejected it. That case will produce a
different message, as shown in Section 20.15.) Other error messages
such as Connection timed out might
indicate more fundamental problems, like lack of network
connectivity.