The Message Queue Installer’s JDK Selection screen is not the only way to specify a version of the Java Runtime Environment for Message Queue to use. The JRE used by the Message Queue command line utilities (imqadmin, imqbrokerd, imqcmd, imqobjmgr, imqdbmgr, imqusermgr, imqkeytool) is determined by the following sources, in order of precedence:
The -jrehome or -javahome command line option to the imqbrokerd command. (If both are specified, the one occurring last on the command line takes precedence).
The J2SE file location specified in the jdk.env file. (This file is deprecated, but is still supported for backward compatibility. For historical reasons, it has higher priority than anything else except option 1.)
The IMQ_JAVAHOME environment variable.
The environment variable IMQ_DEFAULT_JAVAHOME in the imqenv.conf file.
The system default locations, as specified in the documentation for your platform.
To check which version of the Java runtime Message Queue will use, enter the command
The output from this command includes the version and pathname of the configured JRE: for example,
Java Runtime: 1.5.0_12 Sun Microsystems Inc. /usr/java/jdk1.5.0_12/jre
When you specify a JRE location through the Installer’s JDK Selection screen, the Installer saves that location as the value of IMQ_DEFAULT_JAVAHOME in the imqenv.conf file (option 4 in the list above). On Linux, this file is located at
After a successful Message Queue installation, it should include something like the following:
You can override this setting, however, either by editing the imqenv.conf file or by setting one of the other options higher in the list. This can be useful, for instance, for testing or reconfiguring the broker when a newer JRE version becomes available. Understanding how the JRE is determined can also help in troubleshooting problems. For instance, if the imqbrokerd -version command shows that Message Queue is using an unexpected JRE, it may be that one of the higher-precedence options has been set inadvertently (such as by an old jdk.env file that should have been deleted).