Re: ORA-27101: shared memory realm does not exist

A few common problems with XE installations:

1. If XE was installed by a Domain Administrator, XE may not install correctly. The actual problems vary depending on the Domain Administrator's real capabilities and range from complete failure (while appearing to install, based on the setup response) to 'crippled install with various problems'.

Solution: install as a local XP administrator.

2) If XE was installed on a machine using DHCP, and loopback adapter was not used, XE may install correctly but fail after the IP expired and was not renewed to the same adddress. This may occur after one or more reboots. The problems are usually isolated to the listener interaction, as the listener.ora indicates the host at XE install time and that may change. One interesting effect is that local SQLPlus logons on the local machine work (bequeath adapter) whereas remote accesses 'can not display the database home page' - Oracle's new HTTP listener technique uses the database listener.

Solution: install with a loopback adapter, and/or keep listener.ora up to date

3) If XE was installed on the a machine that previously hosted an older version of Oracle, interesting failures (usually during install) will be observed due to conflicting pieces in the registry and/or stray DLLs.

Solution: clean the machine thoroughly and reinstall

4) If firewalls are used, they may block ports 1521 and/or 8080 (the default APEX port). On Linux, these may be inadvertently activated using SELinux. Symptoms are often similar to listener.ora failures

Solution: properly configure firewalls and SELinux, or disable these utilities

5) On XP, a number of issues have seen seen when installing on drives other than C: which seem to relate to 'directory permission inheritance' on other drives. These may be simply local policies at the site of the people installing, but are troublesome. The symptoms are often apparent install, but no database filess or alert_xe.log

Solution: ensure installing user and Oracle really have permission to create directories and files on the drive

These, and a lot more, are discussed in the Oracle Discussion Forum specific to XE. To access that, access the OTN discussion forums, sign in and look for the XE forum. If it does not show up, you need to register - search for 'register XE' in the Database-General forum for steps.

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Hans Forbrich   (mailto: Fuzzy.GreyBeard_at_gmail.com)   


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