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3.3.1 Server Start-up Failures

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 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

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 may be a different problem. For example, trying to start a server on a reserved port number may draw something like:

$ 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

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 may 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 may 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 3.4.1 Shared Memory and Semaphores.