There are several common reasons for the postmaster to fail to start up. Check the postmaster's log file, or start it by hand (without redirecting standard output or standard error) to see what complaint messages appear. Some of the possible error messages are reasonably self-explanatory, but here are some that are not:
FATAL: StreamServerPort: bind() failed: Address already in use Is another postmaster already running on that port?This usually means just what it suggests: you accidentally started a second postmaster 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 wording, there may be a different problem. For example, trying to start a postmaster on a reserved port number may draw something like
$ postmaster -i -p 666 FATAL: StreamServerPort: bind() failed: Permission denied Is another postmaster already running on that port?
IpcMemoryCreate: shmget failed (Invalid argument) key=5440001, size=83918612, permission=600 FATAL 1: ShmemCreate: cannot create regionA message like this probably means that your kernel's limit on the size of shared memory areas is smaller than the buffer area that Postgres is trying to create. (Or it could mean that you don't have SysV-style shared memory support configured into your kernel at all.) As a temporary workaround, you can try starting the postmaster with a smaller-than-normal number of buffers (-B switch). You will eventually want to reconfigure your kernel to increase the allowed shared memory size, however. You may see this message when trying to start multiple postmasters on the same machine, if their total space requests exceed the kernel limit.
IpcSemaphoreCreate: semget failed (No space left on device) key=5440026, num=16, permission=600A message like this does not mean that you've run out of disk space; it means that your kernel's limit on the number of SysV semaphores is smaller than the number Postgres wants to create. As above, you may be able to work around the problem by starting the postmaster with a reduced number of backend processes (-N switch), but you'll eventually want to increase the kernel limit.