4.3BSD-UWisc/man/cat3/signal.3c
SIGNAL(3C) UNIX Programmer's Manual SIGNAL(3C)
NAME
signal - simplified software signal facilities
SYNOPSIS
#include <signal.h>
(*signal(sig, func))()
int (*func)();
DESCRIPTION
_S_i_g_n_a_l is a simplified interface to the more general
_s_i_g_v_e_c(2) facility.
A signal is generated by some abnormal event, initiated by a
user at a terminal (quit, interrupt, stop), by a program
error (bus error, etc.), by request of another program
(kill), or when a process is stopped because it wishes to
access its control terminal while in the background (see
_t_t_y(4)). Signals are optionally generated when a process
resumes after being stopped, when the status of child
processes changes, or when input is ready at the control
terminal. Most signals cause termination of the receiving
process if no action is taken; some signals instead cause
the process receiving them to be stopped, or are simply dis-
carded if the process has not requested otherwise. Except
for the SIGKILL and SIGSTOP signals, the _s_i_g_n_a_l call allows
signals either to be ignored or to cause an interrupt to a
specified location. The following is a list of all signals
with names as in the include file <_s_i_g_n_a_l._h>:
SIGHUP 1 hangup
SIGINT 2 interrupt
SIGQUIT 3* quit
SIGILL 4* illegal instruction
SIGTRAP 5* trace trap
SIGIOT 6* IOT instruction
SIGEMT 7* EMT instruction
SIGFPE 8* floating point exception
SIGKILL 9 kill (cannot be caught or ignored)
SIGBUS 10* bus error
SIGSEGV 11* segmentation violation
SIGSYS 12* bad argument to system call
SIGPIPE 13 write on a pipe with no one to read it
SIGALRM 14 alarm clock
SIGTERM 15 software termination signal
SIGURG 16@ urgent condition present on socket
SIGSTOP 17'|+'stop (cannot be caught or ignored)
SIGTSTP 18'|+'stop signal generated from keyboard
SIGCONT 19@ continue after stop
SIGCHLD 20@ child status has changed
SIGTTIN 21'|+'background read attempted from control terminal
SIGTTOU 22'|+'background write attempted to control terminal
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SIGNAL(3C) UNIX Programmer's Manual SIGNAL(3C)
SIGIO 23@ i/o is possible on a descriptor (see _f_c_n_t_l(2))
SIGXCPU 24 cpu time limit exceeded (see _s_e_t_r_l_i_m_i_t(2))
SIGXFSZ 25 file size limit exceeded (see _s_e_t_r_l_i_m_i_t(2))
SIGVTALRM 26 virtual time alarm (see _s_e_t_i_t_i_m_e_r(2))
SIGPROF 27 profiling timer alarm (see _s_e_t_i_t_i_m_e_r(2))
SIGWINCH 28@ Window size change
SIGUSR1 30 User defined signal 1
SIGUSR2 31 User defined signal 2
The starred signals in the list above cause a core image if
not caught or ignored.
If _f_u_n_c is SIG_DFL, the default action for signal _s_i_g is
reinstated; this default is termination (with a core image
for starred signals) except for signals marked with @ or
'|+'. Signals marked with @ are discarded if the action is
SIG_DFL; signals marked with '|+' cause the process to stop.
If _f_u_n_c is SIG_IGN the signal is subsequently ignored and
pending instances of the signal are discarded. Otherwise,
when the signal occurs further occurrences of the signal are
automatically blocked and _f_u_n_c is called.
A return from the function unblocks the handled signal and
continues the process at the point it was interrupted.
Unlike previous signal facilities, the handler _f_u_n_c remains
installed after a signal has been delivered.
If a caught signal occurs during certain system calls, caus-
ing the call to terminate prematurely, the call is automati-
cally restarted. In particular this can occur during a _r_e_a_d
or _w_r_i_t_e(2) on a slow device (such as a terminal; but not a
file) and during a _w_a_i_t(2).
The value of _s_i_g_n_a_l is the previous (or initial) value of
_f_u_n_c for the particular signal.
After a _f_o_r_k(2) or _v_f_o_r_k(2) the child inherits all signals.
_E_x_e_c_v_e(2) resets all caught signals to the default action;
ignored signals remain ignored.
RETURN VALUE
The previous action is returned on a successful call. Oth-
erwise, -1 is returned and _e_r_r_n_o is set to indicate the
error.
ERRORS
_S_i_g_n_a_l will fail and no action will take place if one of the
following occur:
[EINVAL] _S_i_g is not a valid signal number.
[EINVAL] An attempt is made to ignore or supply a
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SIGNAL(3C) UNIX Programmer's Manual SIGNAL(3C)
handler for SIGKILL or SIGSTOP.
[EINVAL] An attempt is made to ignore SIGCONT (by
default SIGCONT is ignored).
SEE ALSO
kill(1), ptrace(2), kill(2), sigvec(2), sigblock(2), sigset-
mask(2), sigpause(2), sigstack(2), setjmp(3), tty(4)
NOTES (VAX-11)
The handler routine can be declared:
handler(sig, code, scp)
Here _s_i_g is the signal number, into which the hardware
faults and traps are mapped as defined below. Code is a
parameter which is either a constant as given below or, for
compatibility mode faults, the code provided by the
hardware. _S_c_p is a pointer to the _s_t_r_u_c_t _s_i_g_c_o_n_t_e_x_t used by
the system to restore the process context from before the
signal. Compatibility mode faults are distinguished from
the other SIGILL traps by having PSL_CM set in the psl.
The following defines the mapping of hardware traps to sig-
nals and codes. All of these symbols are defined in
<_s_i_g_n_a_l._h>:
Hardware condition Signal Code
Arithmetic traps:
Integer overflow SIGFPE FPE_INTOVF_TRAP
Integer division by zero SIGFPE FPE_INTDIV_TRAP
Floating overflow trap SIGFPE FPE_FLTOVF_TRAP
Floating/decimal division by zero SIGFPE FPE_FLTDIV_TRAP
Floating underflow trap SIGFPE FPE_FLTUND_TRAP
Decimal overflow trap SIGFPE FPE_DECOVF_TRAP
Subscript-range SIGFPE FPE_SUBRNG_TRAP
Floating overflow fault SIGFPE FPE_FLTOVF_FAULT
Floating divide by zero fault SIGFPE FPE_FLTDIV_FAULT
Floating underflow fault SIGFPE FPE_FLTUND_FAULT
Length access control SIGSEGV
Protection violation SIGBUS
Reserved instruction SIGILL ILL_RESAD_FAULT
Customer-reserved instr. SIGEMT
Reserved operand SIGILL ILL_PRIVIN_FAULT
Reserved addressing SIGILL ILL_RESOP_FAULT
Trace pending SIGTRAP
Bpt instruction SIGTRAP
Compatibility-mode SIGILL hardware supplied code
Chme SIGSEGV
Chms SIGSEGV
Chmu SIGSEGV
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SIGNAL(3C) UNIX Programmer's Manual SIGNAL(3C)
Printed 12/27/86 May 20, 1986 4