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[Sorin Sbârnea <sorin.sbarnea@xxxxxxxxx>]

I have the same problem with latest LTS Ubuntu, and the proper solution
is to set BOTH SHMMAX and SHMALL to the same value, the best is ¼ of
total memory.

kernel.shmmax = xxx
kernel.shmall = xxx

Still, I would consider this an real bug, especially because the
postgres error is misleading and incomplete.

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https://bugs.launchpad.net/bugs/264336

Title:
  pgsql fails to start due to shared buffer setting greater than kernel
  allows

Status in “linux” package in Ubuntu:
  Won't Fix
Status in “postgresql-8.3” package in Ubuntu:
  Won't Fix
Status in “postgresql-9.1” package in Ubuntu:
  Confirmed
Status in “postgresql-common” package in Ubuntu:
  Invalid
Status in “linux” source package in Jaunty:
  Won't Fix
Status in “postgresql-8.3” source package in Jaunty:
  Won't Fix
Status in “postgresql-9.1” source package in Jaunty:
  Invalid
Status in “postgresql-common” source package in Jaunty:
  Invalid

Bug description:
  Binary package hint: postgresql-8.3

  Freshly installed pgsql 8.3 on hardy got me this error when restarting:
  2008-09-03 09:16:39 EDT DETAIL:  Failed system call was shmget(key=5432001, size=38207488, 03600).
  2008-09-03 09:16:39 EDT 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 38207488 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.

  Checking the kernel settings:
  sudo sysctl -a | grep -i shm
  kernel.shmmax = 33554432
  kernel.shmall = 2097152
  kernel.shmmni = 4096

  The shared_buffers setting defaults to 32MB. I changed this down to
  25MB to test and then the server would start right up.

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