2000-11-12postmaster1ApplicationpostmasterPostgreSQL multi-user database serverpostmaster-A 01-B nbuffers-c name=value-d debug-level-D datadir-F-h hostname-i-k filename-l-N max-connections-o extra-options-p port-S-n-sDescriptionpostmaster is the
PostgreSQL multi-user database server.
In order for a client application to access a database it connects
(over a network or locally) to a running
postmaster. The
postmaster then starts a separate server
process () to handle the connection.
The postmaster also manages the communication among server
processes.
By default the postmaster starts in the foreground and prints log
messages to the standard output. In practical applications the
postmaster should be started as a background process, perhaps at
boot time.
One postmaster always manages the data from exactly one database
cluster. A database cluster is a collection of databases that is
stored at a common file system location. When the postmaster
starts it needs to know the location of the database cluster files
(data area). This is done with the
invocation option or the PGDATA
environment variable, there is no default. More than one
postmaster process can run on a system at one time, as long as they
use different data areas and different port numbers (see below). A
data area is created with .
Optionspostmaster accepts the following
command line arguments. For a detailed discussion of the options
consult the Administrator's Guide. You can
also save typing most of these options by setting up a
configuration file.
-A 0|1
Enables run-time assert checks, which is a debugging aid to
detect programming mistakes. This is only available if it was
enabled during compilation. If so, the default is on.
-B nbuffers
Sets the number of shared buffers for use by the server
processes. This value defaults to 64 buffers, where each
buffer is 8 kB.
-c name=value
Sets a named run-time parameter. Consult the
Administrator's Guide for a list and
descriptions. Most of the other command line options are in
fact short forms of such a parameter assignment.
On some systems it is also possible to equivalently use
GNU-style long options in the form
--name=value.
-d debug-level
Sets the debug level. The higher this value is set, the more
debugging output is written to the server log. The default is
0, which means no debugging. Values up to 4 make sense.
-D datadir
Specifies the file system location of the data directory. See
discussion above.
-F
Disables fsync calls for performance
improvement at the risk of data corruption. Read the detailed
documentation before using this!
-h hostname
Specifies the TCP/IP hostname or address on which the
postmaster is to listen for
connections from client applications. Defaults to the value
of the PGHOST environment variable, or if
PGHOST is not set, it defaults to listening on
all configured addresses (including localhost).
-i
Allows clients to connect via TCP/IP (Internet domain)
connections. Without this option, only local Unix domain
socket connections are accepted.
-k filename
Specifies the Unix domain socket file name on which the
postmaster is to listen for
connections from client applications. Defaults to the value
of the PGUNIXSOCKET environment variable, or if
PGUNIXSOCKET is not set, then defaults to a
file in /tmp constructed from the port
number.
-l
Enables secure connections using SSL. The
option is also required. You must have compiled with SSL
enabled to use this option.
-N max-connections
Sets the maximum number of client connections that this
postmaster will accept. By default, this value is 32, but it
can be set as high as 1024 if your system will support that
many processes. (Note that is required to
be at least twice .)
-o extra-options
The command line-style options specified in EXTRA-OPTIONS are passed to
all backend server processes started by this
postmaster. See for
possibilities. If the option string contains any spaces, the
entire string must be quoted.
-p port
Specifies the TCP/IP port or local Unix domain socket file
extension on which the postmaster
is to listen for connections from client applications.
Defaults to the value of the PGPORT environment
variable, or if PGPORT is not set, then
defaults to the value established during compilation (normally
5432). If you specify a port other than the default port,
then all client applications must specify the same port using
either command-line options or PGPORT.
-S
Specifies that the postmaster
process should start up in silent mode. That is, it will
disassociate from the user's (controlling) terminal, start its
own process group, and redirect its standard output and
standard error to /dev/null.
Using this switch discards all logging output, which is
probably not what you want, since it makes it very difficult
to troubleshoot problems. See below for a better way to start
the postmaster in the background.
Two additional command line options are available for debugging
problems that cause a backend to die abnormally. These options
control the behavior of the postmaster
in this situation, and neither option is intended for
use in ordinary operation.
The ordinary strategy for this situation is to notify all other
backends that they must terminate and then reinitialize the shared
memory and semaphores. This is because an errant backend could
have corrupted some shared state before terminating.
These special-case options are:
-npostmaster
will not reinitialize shared data structures. A knowledgeable system
programmer can then use a debugger
to examine shared memory and semaphore state.
-spostmaster
will stop all other backend processes by sending the signal
SIGSTOP,
but will not cause them to terminate. This permits system programmers
to collect core dumps from all backend processes by hand.
Outputs
semget: No space left on device
If you see this message, you should run the
ipcclean
command. After doing so, try starting
postmaster
again. If this still doesn't work, you probably need to configure
your kernel for shared memory and semaphores as described in the
installation notes. If you run multiple instances of
postmaster
on a single host, or have a kernel with particularly small shared memory
and/or semaphore limits, you may have to reconfigure your kernel to increase
its shared memory or semaphore parameters.
You may be able to postpone
reconfiguring your kernel by decreasing -B to reduce
Postgres' shared memory
consumption, and/or by reducing -N to reduce Postgres' semaphore
consumption.
StreamServerPort: cannot bind to port
If you see this message, you should make certain that there is no
other postmaster
process already running on the same port number. The easiest way to
determine this is by using the command
$ ps -ax | grep postmaster
on BSD-based systems, or
$ ps -e | grep postmast
for System V-like or POSIX-compliant systems such as HP-UX.
If you
are sure that no other
postmaster
processes are running and you still get this error, try specifying a
different port using the
-p
option. You may also get this error if you terminate the
postmaster
and immediately restart it using the same port; in this case, you must
simply wait a few seconds until the operating system closes the port
before trying again. Finally, you may get this error if you specify
a port number that your operating system considers to be reserved.
For example, many versions of Unix consider port numbers under 1024 to
be trusted
and only permit the Unix superuser to access them.
IpcMemoryAttach: shmat() failed: Permission denied
A likely explanation is that another user attempted to start a
postmaster
process on the same port which acquired shared resources and then
died. Since Postgres shared memory keys are based on the port number
assigned to the
postmaster,
such conflicts are likely if there is more than one installation on
a single host. If there are no other
postmaster
processes currently running (see above), run
ipcclean
and try again. If other postmaster
images
are running, you will have to find the owners of those processes to
coordinate the assignment of port numbers and/or removal of unused
shared memory segments.
Notes
If at all possible, do not use
SIGKILL to kill the
postmaster. This will prevent
postmaster from freeing the system
resources (e.g., shared memory and semaphores) that it holds before
terminating.
To terminate the postmaster normally, the signals
SIGTERM, SIGINT, or
SIGQUIT can be used. The first will wait for
all clients to terminate before quitting, the second will
forcefully disconnect all clients, and the third will quit
immediately without lengthy shutdown, resulting in a recovery run
during restart.
The utility command can be used to
start and shut down the postmaster safely and comfortably.
Usage
To start postmaster in the background
using default values, type:
$nohup postmaster >logfile 2>&1 </dev/null &
To start postmaster with a specific
port:
$postmaster -p 1234
This command will start up postmaster
communicating through the port 1234. In order to connect to this
postmaster using psql, you would need to
run it as
$psql -p 1234
or set the environment variable PGPORT:
$export PGPORT=1234$psql