shared memory segment exceeded your kernel's SHMMAX parameter

http://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server

IpcMemoryCreate: shmget(key=5432001, size=415776768, 03600) failed: Invalid argument 

This error usually means that PostgreSQL's request for a shared memory
segment exceeded your kernel's SHMMAX parameter. You can either
reduce the request size or reconfigure the kernel with larger SHMMAX.
To reduce the request size (currently 415776768 bytes), reduce
PostgreSQL's shared_buffers parameter (currently 50000) and/or
its max_connections parameter (currently 12).

http://www.postgresql.org/docs/current/static/kernel-resources.html
Linux

The default maximum segment size is 32 MB, which is only adequate for very small PostgreSQL installations. The default maximum total size is 2097152 pages. A page is almost always 4096 bytes except in unusual kernel configurations with "huge pages" (use getconf PAGE_SIZE to verify). That makes a default limit of 8 GB, which is often enough, but not always.

The shared memory size settings can be changed via the sysctl interface. For example, to allow 16 GB:

$ sysctl -w kernel.shmmax=17179869184$ sysctl -w kernel.shmall=4194304

In addition these settings can be preserved between reboots in the file /etc/sysctl.conf. Doing that is highly recommended.

Ancient distributions might not have the sysctl program, but equivalent changes can be made by manipulating the/proc file system:

$ echo 17179869184 >/proc/sys/kernel/shmmax$ echo 4194304 >/proc/sys/kernel/shmall

The remaining defaults are quite generously sized, and usually do not require changes.