siginfo(3) manual page

A process may request signal information when it is catching a signal. The information specifies why the system generated that signal. To request signal information in a signal handler, the user can set SA_SIGINFO in sa_flags before sigaction(2) is called, otherwise the user can use sigwaitinfo(2) and sigtimedwait(2) to get signal information. In either case, the system returns the information in a structure of type siginfo_t, which includes the following information:

Type	Member	Description
int	si_signo	signal number
int	si_errno	error number
int	si_code	signal code
union sigval	si_value	signal value
pid_t	si_pid	sending process ID
uid_t	si_uid	sending process's real user ID
void	*si_addr	address of faulting instruction
int	si_status	exit value or signal
long	si_band	band event for `SIGPOLL`
int	si_trapno	machine trap code
int	si_timerid	POSIX timer ID
int	si_overrun	POSIX timer overrun count
int	si_mqd	POSIX message queue ID

The si_signo member contains the signal number.

The si_errno member contains an error number defined in the file <errno.h>.

The si_code member contains a code which describes the cause of the signal. The macros specified in the Code column of the following table are defined for use as values of si_code that are signal-specific or non-signal-specific reasons why the signal was generated:

Signal Code Reason
SIGILL ILL_ILLOPC illegal opcode
ILL_ILLOPN illegal operand
ILL_ILLADR illegal addressing mode
ILL_ILLTRP illegal trap
ILL_PRVOPC illegal privileged opcode
ILL_PRVREG illegal privileged register
ILL_COPROC coprocessor error
ILL_BADSTK internal stack error
SIGFPE FPE_INTDIV integer divide by zero
FPE_INTOVF integer overflow
FPE_FLTDIV floating-point divide by zero
FPE_FLTOVF floating-point overflow
FPE_FLTUND floating-point underflow
FPE_FLTRES floating-point inexact result
FPE_FLTINV invalid floating-point operation
FPE_FLTSUB subscript out of range
SIGSEGV SEGV_MAPERR address not mapped to object
SEGV_ACCERR invalid permissions for mapped object
SIGBUS BUS_ADRALN invalid address alignment
BUS_ADRERR nonexistent physical address
BUS_OBJERR object-specific hardware error
BUS_OOMERR cannot alloc a page to map at fault
SIGTRAP TRAP_BRKPT process breakpoint
TRAP_TRACE process trace trap
TRAP_DTRACE DTrace induced trap
TRAP_CAP capabilities protective trap
SIGCHLD CLD_EXITED child has exited
CLD_KILLED child has terminated abnormally and did not create a core file
CLD_DUMPED child has terminated abnormally and created a core file
CLD_TRAPPED traced child has trapped
CLD_STOPPED child has stopped
CLD_CONTINUED stopped child has continued
SIGPOLL POLL_IN data input available
POLL_OUT output buffers available
POLL_MSG input message available
POLL_ERR I/O error
POLL_PRI high priority input available
POLL_HUP device disconnected

Any SI_NOINFO Only the si_signo member is meaningful; the value of all other members is unspecified.
SI_USER signal sent by kill(2)
SI_QUEUE signal sent by sigqueue(2)
SI_TIMER signal generated by expiration of a timer set by timer_settime(2)
SI_ASYNCIO signal generated by completion of an asynchronous I/O request
SI_MESGQ signal generated by arrival of a message on an empty message queue
SI_KERNEL signal generated by miscellaneous parts of the kernel
SI_LWP signal sent by pthread_kill(3)

In addition, the following signal-specific information is available:

Signal Member Value
SIGILL si_addr address of faulting instruction
si_trapno machine dependent of trap code
SIGFPE si_addr address of faulting instruction
si_trapno machine dependent of trap code
SIGSEGV si_addr address of faulting memory reference
si_trapno machine dependent of trap code
SIGBUS si_addr address of faulting instruction
si_trapno machine dependent of trap code
SIGCHLD si_pid child process ID
si_status exit value or signal; if si_code is equal to CLD_EXITED, then it is equal to the exit value of the child process, otherwise, it is equal to a signal that caused the child process to change state.
si_uid real user ID of the process that sent the signal
SIGPOLL si_band band event for POLL_IN, POLL_OUT, or POLL_MSG

Finally, the following code-specific information is available:

Code Member Value
SI_USER si_pid the process ID that sent the signal
si_uid real user ID of the process that sent the signal
SI_QUEUE si_value the value passed to sigqueue(2) system call
si_pid the process ID that sent the signal
si_uid real user ID of the process that sent the signal
SI_TIMER si_value the value passed to timer_create(2) system call
si_timerid the timer ID returned by timer_create(2) system call
si_overrun timer overrun count corresponding to the signal
si_errno If timer overrun will be { DELAYTIMER_MAX}, an error code defined in <errno.h> is set
SI_ASYNCIO si_value the value passed to aio system calls
SI_MESGQ si_value the value passed to mq_notify(2) system call
si_mqd the ID of the message queue which generated the signal
SI_LWP si_pid the process ID that sent the signal
si_uid real user ID of the process that sent the signal

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Manual Pages — SIGINFO

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Signal	Code	Reason
`SIGILL`	`ILL_ILLOPC`	illegal opcode
	`ILL_ILLOPN`	illegal operand
	`ILL_ILLADR`	illegal addressing mode
	`ILL_ILLTRP`	illegal trap
	`ILL_PRVOPC`	illegal privileged opcode
	`ILL_PRVREG`	illegal privileged register
	`ILL_COPROC`	coprocessor error
	`ILL_BADSTK`	internal stack error
`SIGFPE`	`FPE_INTDIV`	integer divide by zero
	`FPE_INTOVF`	integer overflow
	`FPE_FLTDIV`	floating-point divide by zero
	`FPE_FLTOVF`	floating-point overflow
	`FPE_FLTUND`	floating-point underflow
	`FPE_FLTRES`	floating-point inexact result
	`FPE_FLTINV`	invalid floating-point operation
	`FPE_FLTSUB`	subscript out of range
`SIGSEGV`	`SEGV_MAPERR`	address not mapped to object
	`SEGV_ACCERR`	invalid permissions for mapped object
`SIGBUS`	`BUS_ADRALN`	invalid address alignment
	`BUS_ADRERR`	nonexistent physical address
	`BUS_OBJERR`	object-specific hardware error
	`BUS_OOMERR`	cannot alloc a page to map at fault
`SIGTRAP`	`TRAP_BRKPT`	process breakpoint
	`TRAP_TRACE`	process trace trap
	`TRAP_DTRACE`	DTrace induced trap
	`TRAP_CAP`	capabilities protective trap
`SIGCHLD`	`CLD_EXITED`	child has exited
	`CLD_KILLED`	child has terminated abnormally and did not create a core file
	`CLD_DUMPED`	child has terminated abnormally and created a core file
	`CLD_TRAPPED`	traced child has trapped
	`CLD_STOPPED`	child has stopped
	`CLD_CONTINUED`	stopped child has continued
`SIGPOLL`	`POLL_IN`	data input available
	`POLL_OUT`	output buffers available
	`POLL_MSG`	input message available
	`POLL_ERR`	I/O error
	`POLL_PRI`	high priority input available
	`POLL_HUP`	device disconnected
Any	`SI_NOINFO`	Only the si_signo member is meaningful; the value of all other members is unspecified.
	`SI_USER`	signal sent by kill(2)
	`SI_QUEUE`	signal sent by sigqueue(2)
	`SI_TIMER`	signal generated by expiration of a timer set by timer_settime(2)
	`SI_ASYNCIO`	signal generated by completion of an asynchronous I/O request
	`SI_MESGQ`	signal generated by arrival of a message on an empty message queue
	`SI_KERNEL`	signal generated by miscellaneous parts of the kernel
	`SI_LWP`	signal sent by pthread_kill(3)

Signal	Member	Value
`SIGILL`	si_addr	address of faulting instruction
	si_trapno	machine dependent of trap code
`SIGFPE`	si_addr	address of faulting instruction
	si_trapno	machine dependent of trap code
`SIGSEGV`	si_addr	address of faulting memory reference
	si_trapno	machine dependent of trap code
`SIGBUS`	si_addr	address of faulting instruction
	si_trapno	machine dependent of trap code
`SIGCHLD`	si_pid	child process ID
	si_status	exit value or signal; if si_code is equal to `CLD_EXITED`, then it is equal to the exit value of the child process, otherwise, it is equal to a signal that caused the child process to change state.
	si_uid	real user ID of the process that sent the signal
`SIGPOLL`	si_band	band event for `POLL_IN, POLL_OUT`, or `POLL_MSG`