postgresql-8.4 8.4.5-0ubuntu10.04 failed to upgrade

Binary package hint: postgresql-8.4

On upgrading postgresql. The first error that occurs is:

 * Starting PostgreSQL 8.4 database server
 * The PostgreSQL server failed to start. Please check the log output:
2010-10-11 13:19:52 BST FATAL: could not create shared memory segment: Invalid argument
2010-10-11 13:19:52 BST DETAIL: Failed system call was shmget(key=5432001, size=36880384, 03600).
2010-10-11 13:19:52 BST HINT: 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 36880384 bytes), reduce PostgreSQL's shared_buffers parameter (currently 4096) and/or its max_connections parameter (currently 103).
 If the request size is already small, it's possible that it is less than your kernel's SHMMIN parameter, in which case raising the request size or reconfiguring SHMMIN is called for.
 The PostgreSQL documentation contains more information about shared memory configuration.

Not being knowledgeable in this area: is this an item of user configuration, or something that needs a deeper fix?

ProblemType: Package
DistroRelease: Ubuntu 10.04
Package: postgresql-8.4 8.4.5-0ubuntu10.04
ProcVersionSignature: Ubuntu 2.6.32-25.44-generic 2.6.32.21+drm33.7
Uname: Linux 2.6.32-25-generic i686
NonfreeKernelModules: fglrx
Architecture: i386
Date: Mon Oct 11 13:15:47 2010
ErrorMessage: subprocess installed post-installation script returned error exit status 1
SourcePackage: postgresql-8.4
Title: package postgresql-8.4 8.4.5-0ubuntu10.04 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1