Sorry, I should have clarified my intention for this local VM - I've installed Oracle 11i rel 2 DB, which was fine, but when I tried starting the database, I get '[ORA-00845: MEMORY_TARGET not supported on this system]' - Oracle has shared memory requirements over and above what is reasonable.
So I *could* change oracle parameters to make it match what the OS thinks is reasonable, but having tried temporarily remounting /dev/shm as a larger space, this did allow me start the DB. I have also increased the memory allocated to the VM to help reduce the chances of actually having to use this space.
[root@localhost ~]# ls -l /dev/shm
-r-------- 1 inquira inquira 67108904 Jan 27 09:09 pulse-shm-1154165621
-r-------- 1 gdm gdm 67108904 Jan 27 09:08 pulse-shm-1196137821
-r-------- 1 inquira inquira 67108904 Jan 27 09:08 pulse-shm-2888496656
-r-------- 1 inquira inquira 67108904 Jan 27 09:09 pulse-shm-3746723676
-r-------- 1 inquira inquira 67108904 Jan 27 09:08 pulse-shm-3928996198
-r-------- 1 gdm gdm 67108904 Jan 27 09:08 pulse-shm-4036240913
but I gather that's allocated memory rather than used memory:
[root@localhost ~]# du -h /dev/shm/*
So, anyway - I added the line:
tmpfs /dev/shm tmpfs size=4g 0 0
to /etc/fstab and issued:
mount -o remount tmpfs
so this seems to have done the trick and overriden the default:
[root@localhost ~]# df | grep /dev/shm
tmpfs 4194304 232 4194072 1% /dev/shm
and my database starts:
[root@localhost ~]# su - oracle
[oracle@localhost ~]$ sqlplus / AS SYSDBA
SQL*Plus: Release 220.127.116.11.0 Production on Fri Jan 27 09:36:05 2012
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to an idle instance.
ORACLE instance started.
Total System Global Area 1048059904 bytes
Fixed Size 2219992 bytes
Variable Size 629145640 bytes
Database Buffers 411041792 bytes
Redo Buffers 5652480 bytes
And this of course also works after a reboot.
So - thanks for your help - not an ideal memory configuration, I know, but I can play with the settings once I have a stable installation on my VM.