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Nonstandard Signals

Particular operating systems support additional signals not listed above. The ANSI C standard reserves all identifiers beginning with `SIG' followed by an uppercase letter for the names of signals. You should consult the documentation or header files for your particular operating system and processor type to find out about the specific signals it supports.

For example, some systems support extra signals which correspond to hardware traps. Some other kinds of signals commonly supported are used to implement limits on CPU time or file system usage, asynchronous changes to terminal configuration, and the like. Systems may also define signal names that are aliases for standard signal names.

You can generally assume that the default action (or the action set up by the shell) for implementation-defined signals is reasonable, and not worry about them yourself. In fact, it's usually a bad idea to ignore or block signals you don't know anything about, or try to establish a handler for signals whose meanings you don't know.

Here are some of the other signals found on commonly used operating systems:

SIGCLD

Obsolete name for SIGCHLD.

SIGTRAP

Generated by the machine's breakpoint instruction. Used by debuggers. Default action is to dump core.

SIGIOT

Generated by the PDP-11 "iot" instruction; equivalent to SIGABRT. Default action is to dump core.

SIGEMT

Emulator trap; this results from certain unimplemented instructions. It is a program error signal.

SIGSYS

Bad system call; that is to say, the instruction to trap to the operating system was executed, but the code number for the system call to perform was invalid. This is a program error signal.

SIGPOLL

This is a System V signal name, more or less similar to SIGIO.

SIGXCPU

CPU time limit exceeded. This is used for batch processing. Default action is program termination.

SIGXFSZ

File size limit exceeded. This is used for batch processing. Default action is program termination.

SIGWINCH

Window size change. This is generated on certain systems when the size of the current window on the screen is changed. Default action is to ignore it.

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