Java Platform, Standard Edition Troubleshooting Guide
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Signals Used in Oracle Solaris and Linux

Signals tagged as "optional" are not used when the -Xrs option is specified to reduce signal usage. With this option fewer signals are used, although the VM installs its own signal handler for essential signals such as SIGSEGV. Specifying this option means that the shutdown hook mechanism will not execute if the process receives a SIGQUIT, SIGTERM, SIGINT, or SIGHUP. Shutdown hooks will execute, as expected, if the VM terminates normally (that is, when the last non-daemon thread completes or the System.exit method is invoked).

On Oracle Solaris 8 and 9 operating system, signals tagged as "configurable" are substituted when the -XX:+UseAltSigs option is specified to use alternative signals. Starting with Oracle Solaris 10 operating system, this option is ignored, as the operating system reserves two additional signals (called SIGJVM1 and SIGJVM2).

On Linux, the handler for SIGUSR1 cannot be overridden. SIGUSR2 is used to implement suspend and resume. However it is possible to specify an alternative signal to be used instead of SIGUSR2. This is done by specifying the _JAVA_SR_SIGNUM environment variable. If this environment variable is set, it must be set to a value larger than the maximum of SIGSEGV and SIGBUS.

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