Advanced Programming in the UNIX® Environment

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Section 10.2 Signal Concepts 319

SIGINT This signal is generated by the terminal driver when we press the

interrupt key (often DELETE or Control-C). This signal is sent to all

processes in the foreground process group (refer to Figure9.9). This

signal is often used to terminate a runaway program, especially when it’s

generating a lot of unwanted output on the screen.

SIGIO This signal indicates an asynchronous I/O event. We discuss it in

Section 14.5.2.

In Figure10.1, we labeled the default action forSIGIOas either ‘‘terminate’’or

‘‘ignore.’’Unfortunately,the default depends on the system. Under System V,

SIGIOis identical toSIGPOLL, so its default action is to terminate the process.

Under BSD, the default is to ignorethe signal.

Linux 3.2.0 and Solaris 10 defineSIGIOto be the same value asSIGPOLL,so

the default behavior is to terminate the process. On FreeBSD 8.0 and Mac OS X

10.6.8, the default is to ignorethe signal.

SIGIOT This indicates an implementation-defined hardwarefault.

The name IOT comes from the PDP-11 mnemonic for the ‘‘input/output TRAP’’

instruction. Earlier versions of System V generated this signal from theabort

function.SIGABRTis now used for this purpose.

On FreeBSD 8.0, Linux 3.2.0, Mac OS X 10.6.8, and Solaris 10,SIGIOTis defined

to be the same value asSIGABRT.

SIGJVM1 Asignal reserved for use by the Java virtual machine on Solaris.

SIGJVM2 Another signal reserved for use by the Java virtual machine on Solaris.

SIGKILL This signal is one of the two that can’t be caught or ignored. It provides

the system administrator with a sureway to kill any process.

SIGLOST This signal is used to notify a process running on a Solaris NFSv4 client

system that a lock could not be reacquired during recovery.

SIGLWP This signal is used internally by the Solaris threads library; it is not

available for general use. On FreeBSD,SIGLWPis defined to be an alias

forSIGTHR.

SIGPIPE If we write to a pipeline but the reader has terminated, SIGPIPEis

generated. Wedescribe pipes in Section 15.2. This signal is also

generated when a process writes to a socket of typeSOCK_STREAMthat

is no longer connected.We describe sockets in Chapter 16.

SIGPOLL This signal is marked obsolescent in SUSv4, so it might be removed in a

futureversion of the standard. It can be generated when a specific event

occurs on a pollable device. We describe this signal with the poll

function in Section 14.4.2. SIGPOLLoriginated with SVR3, and loosely

corresponds to the BSDSIGIOandSIGURGsignals.

On Linux and Solaris,SIGPOLLis defined to have the same value asSIGIO.