Signals used by the JVM

The following Table below shows the signals that are used by the JVM. The signals have been grouped in the table by type or use, as follows:

• Exceptions: The operating system synchronously raises an appropriate exception signal whenever a fatal condition occurs.
• Errors: The JVM raises a SIGABRT if it detects a condition from which it cannot recover.
• Interrupts: Interrupt signals are raised asynchronously, from outside a JVM process, to request shutdown.
• Controls: Other signals that are used by the JVM for control purposes.

Table 2. Signals used by the JVM

Signal Name	Signal type	Description	Disabled by -Xrs
SIGSEGV	Exception	Incorrect access to memory (write to inaccessible memory)	No
SIGILL	Exception	Illegal instruction (attempt to invoke an unknown machine instruction)	No
SIGFPE	Exception	Floating point exception (divide by zero)	No
SIGBUS	Exception	Bus error (attempt to address nonexistent memory location)	Yes
SIGSYS	Exception	Bad system call issued	Yes
SIGXCPU	Exception	CPU time limit exceeded (you have been running too long)	Yes
SIGXFSZ	Exception	File size limit exceeded	Yes
SIGEMT	Exception	EMT instruction (AIX specific)	Yes
SIGABRT	Error	Abnormal termination. The JVM raises this signal whenever it detects a JVM fault.	Yes
SIGINT	Interrupt	Interactive attention (CTRL-C). JVM exits normally.	Yes
SIGTERM	Interrupt	Termination request. JVM will exit normally.	Yes
SIGHUP	Interrupt	Hang up. JVM exits normally.	Yes
SIGQUIT	Control	A quit signal for a terminal. JVM uses this for taking Javadumps.	Yes
SIGTRAP	Control	Internal for use by DBX or ptrace. Used by some JVMs for internal control purposes.	No
SIGPIPE	Control	A write to a pipe that is not being read. JVM ignores this.	No
No Name (40)		An AIX reserved signal. Used by the AIX JVM for internal control purposes.	No

Use the -Xrs (reduce signal usage) option to prevent the JVM from handling most signals. For more information, see Sun's Java application launcher page at.

Do not use the -qflttrap C compiler setting because it provides the possibility of SIGTRAPs being generated, which might then impact the JIT. If you want to have floating point exceptions generated, include this call in your code:

fp_trap( FP_TRAP_SYNC)

so that it generates a SIGFPE signal.

If you install a signal handler for signal numbers 5 (SIGTRAP) or 40, you impact JVM performance because these signals are used for internal control purposes.

Signals 1 (SIGHUP), 2 (SIGINT), 4 (SIGILL), 6 (SIGABRT), 7 (SIGEMT), 8 (SIGFPE), 10 (SIGBUS), 11 (SIGSEGV), 12 (SIGSYS), 15 (SIGTERM), 24 (SIGXCPU) , and 25 (SIGXFSZ) cause the JVM to shut down; therefore, an application signal handler must not attempt to recover from these unless it no longer requires the services of the JVM.