798 lines
19 KiB
Groff
798 lines
19 KiB
Groff
.\" Copyright (c) 1980, 1990, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" From: @(#)sigaction.2 8.2 (Berkeley) 4/3/94
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd September 6, 2013
|
|
.Dt SIGACTION 2
|
|
.Os
|
|
.Sh NAME
|
|
.Nm sigaction
|
|
.Nd software signal facilities
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In signal.h
|
|
.Bd -literal
|
|
struct sigaction {
|
|
void (*sa_handler)(int);
|
|
void (*sa_sigaction)(int, siginfo_t *, void *);
|
|
int sa_flags; /* see signal options below */
|
|
sigset_t sa_mask; /* signal mask to apply */
|
|
};
|
|
.Ed
|
|
.Ft int
|
|
.Fo sigaction
|
|
.Fa "int sig"
|
|
.Fa "const struct sigaction * restrict act"
|
|
.Fa "struct sigaction * restrict oact"
|
|
.Fc
|
|
.Sh DESCRIPTION
|
|
The system defines a set of signals that may be delivered to a process.
|
|
Signal delivery resembles the occurrence of a hardware interrupt:
|
|
the signal is normally blocked from further occurrence, the current thread
|
|
context is saved, and a new one is built.
|
|
A process may specify a
|
|
.Em handler
|
|
to which a signal is delivered, or specify that a signal is to be
|
|
.Em ignored .
|
|
A process may also specify that a default action is to be taken
|
|
by the system when a signal occurs.
|
|
A signal may also be
|
|
.Em blocked
|
|
for a thread,
|
|
in which case it will not be delivered to that thread until it is
|
|
.Em unblocked .
|
|
The action to be taken on delivery is determined at the time
|
|
of delivery.
|
|
Normally, signal handlers execute on the current stack
|
|
of the thread.
|
|
This may be changed, on a per-handler basis,
|
|
so that signals are taken on a special
|
|
.Em "signal stack" .
|
|
.Pp
|
|
Signal routines normally execute with the signal that caused their
|
|
invocation
|
|
.Em blocked ,
|
|
but other signals may yet occur.
|
|
A global
|
|
.Em "signal mask"
|
|
defines the set of signals currently blocked from delivery
|
|
to a thread.
|
|
The signal mask for a thread is initialized
|
|
from that of its parent (normally empty).
|
|
It may be changed with a
|
|
.Xr sigprocmask 2
|
|
or
|
|
.Xr pthread_sigmask 3
|
|
call, or when a signal is delivered to the thread.
|
|
.Pp
|
|
When a signal
|
|
condition arises for a process or thread, the signal is added to a set of
|
|
signals pending for the process or thread.
|
|
Whether the signal is directed at the process in general or at a specific
|
|
thread depends on how it is generated.
|
|
For signals directed at a specific thread,
|
|
if the signal is not currently
|
|
.Em blocked
|
|
by the thread then it is delivered to the thread.
|
|
For signals directed at the process,
|
|
if the signal is not currently
|
|
.Em blocked
|
|
by all threads then it is delivered to one thread that does not have it blocked
|
|
(the selection of which is unspecified).
|
|
Signals may be delivered any time a thread enters the operating system
|
|
(e.g., during a system call, page fault or trap, or clock interrupt).
|
|
If multiple signals are ready to be delivered at the same time,
|
|
any signals that could be caused by traps are delivered first.
|
|
Additional signals may be processed at the same time, with each
|
|
appearing to interrupt the handlers for the previous signals
|
|
before their first instructions.
|
|
The set of pending signals is returned by the
|
|
.Xr sigpending 2
|
|
system call.
|
|
When a caught signal
|
|
is delivered, the current state of the thread is saved,
|
|
a new signal mask is calculated (as described below),
|
|
and the signal handler is invoked.
|
|
The call to the handler
|
|
is arranged so that if the signal handling routine returns
|
|
normally the thread will resume execution in the context
|
|
from before the signal's delivery.
|
|
If the thread wishes to resume in a different context, then it
|
|
must arrange to restore the previous context itself.
|
|
.Pp
|
|
When a signal is delivered to a thread a new signal mask is
|
|
installed for the duration of the process' signal handler
|
|
(or until a
|
|
.Xr sigprocmask 2
|
|
system call is made).
|
|
This mask is formed by taking the union of the current signal mask set,
|
|
the signal to be delivered, and
|
|
the signal mask associated with the handler to be invoked.
|
|
.Pp
|
|
The
|
|
.Fn sigaction
|
|
system call
|
|
assigns an action for a signal specified by
|
|
.Fa sig .
|
|
If
|
|
.Fa act
|
|
is non-zero, it
|
|
specifies an action
|
|
.Dv ( SIG_DFL ,
|
|
.Dv SIG_IGN ,
|
|
or a handler routine) and mask
|
|
to be used when delivering the specified signal.
|
|
If
|
|
.Fa oact
|
|
is non-zero, the previous handling information for the signal
|
|
is returned to the user.
|
|
.Pp
|
|
The above declaration of
|
|
.Vt "struct sigaction"
|
|
is not literal.
|
|
It is provided only to list the accessible members.
|
|
See
|
|
.In sys/signal.h
|
|
for the actual definition.
|
|
In particular, the storage occupied by sa_handler and sa_sigaction overlaps,
|
|
and an application can not use both simultaneously.
|
|
.Pp
|
|
Once a signal handler is installed, it normally remains installed
|
|
until another
|
|
.Fn sigaction
|
|
system call is made, or an
|
|
.Xr execve 2
|
|
is performed.
|
|
A signal-specific default action may be reset by
|
|
setting
|
|
.Va sa_handler
|
|
to
|
|
.Dv SIG_DFL .
|
|
The defaults are process termination, possibly with core dump;
|
|
no action; stopping the process; or continuing the process.
|
|
See the signal list below for each signal's default action.
|
|
If
|
|
.Va sa_handler
|
|
is
|
|
.Dv SIG_DFL ,
|
|
the default action for the signal is to discard the signal,
|
|
and if a signal is pending,
|
|
the pending signal is discarded even if the signal is masked.
|
|
If
|
|
.Va sa_handler
|
|
is set to
|
|
.Dv SIG_IGN
|
|
current and pending instances
|
|
of the signal are ignored and discarded.
|
|
.Pp
|
|
Options may be specified by setting
|
|
.Va sa_flags .
|
|
The meaning of the various bits is as follows:
|
|
.Bl -tag -offset indent -width SA_RESETHANDXX
|
|
.It Dv SA_NOCLDSTOP
|
|
If this bit is set when installing a catching function
|
|
for the
|
|
.Dv SIGCHLD
|
|
signal,
|
|
the
|
|
.Dv SIGCHLD
|
|
signal will be generated only when a child process exits,
|
|
not when a child process stops.
|
|
.It Dv SA_NOCLDWAIT
|
|
If this bit is set when calling
|
|
.Fn sigaction
|
|
for the
|
|
.Dv SIGCHLD
|
|
signal, the system will not create zombie processes when children of
|
|
the calling process exit.
|
|
If the calling process subsequently issues a
|
|
.Xr wait 2
|
|
(or equivalent), it blocks until all of the calling process's child
|
|
processes terminate, and then returns a value of \-1 with
|
|
.Va errno
|
|
set to
|
|
.Er ECHILD .
|
|
The same effect of avoiding zombie creation can also be achieved by setting
|
|
.Va sa_handler
|
|
for
|
|
.Dv SIGCHLD
|
|
to
|
|
.Dv SIG_IGN .
|
|
.It Dv SA_ONSTACK
|
|
If this bit is set, the system will deliver the signal to the process
|
|
on a
|
|
.Em "signal stack" ,
|
|
specified by each thread with
|
|
.Xr sigaltstack 2 .
|
|
.It Dv SA_NODEFER
|
|
If this bit is set, further occurrences of the delivered signal are
|
|
not masked during the execution of the handler.
|
|
.It Dv SA_RESETHAND
|
|
If this bit is set, the handler is reset back to
|
|
.Dv SIG_DFL
|
|
at the moment the signal is delivered.
|
|
.It Dv SA_RESTART
|
|
See paragraph below.
|
|
.It Dv SA_SIGINFO
|
|
If this bit is set, the handler function is assumed to be pointed to by the
|
|
.Va sa_sigaction
|
|
member of
|
|
.Vt "struct sigaction"
|
|
and should match the prototype shown above or as below in
|
|
.Sx EXAMPLES .
|
|
This bit should not be set when assigning
|
|
.Dv SIG_DFL
|
|
or
|
|
.Dv SIG_IGN .
|
|
.El
|
|
.Pp
|
|
If a signal is caught during the system calls listed below,
|
|
the call may be forced to terminate
|
|
with the error
|
|
.Er EINTR ,
|
|
the call may return with a data transfer shorter than requested,
|
|
or the call may be restarted.
|
|
Restart of pending calls is requested
|
|
by setting the
|
|
.Dv SA_RESTART
|
|
bit in
|
|
.Va sa_flags .
|
|
The affected system calls include
|
|
.Xr open 2 ,
|
|
.Xr read 2 ,
|
|
.Xr write 2 ,
|
|
.Xr sendto 2 ,
|
|
.Xr recvfrom 2 ,
|
|
.Xr sendmsg 2
|
|
and
|
|
.Xr recvmsg 2
|
|
on a communications channel or a slow device (such as a terminal,
|
|
but not a regular file)
|
|
and during a
|
|
.Xr wait 2
|
|
or
|
|
.Xr ioctl 2 .
|
|
However, calls that have already committed are not restarted,
|
|
but instead return a partial success (for example, a short read count).
|
|
.Pp
|
|
After a
|
|
.Xr pthread_create 3
|
|
the signal mask is inherited by the new thread and
|
|
the set of pending signals and the signal stack for the new thread are empty.
|
|
.Pp
|
|
After a
|
|
.Xr fork 2
|
|
or
|
|
.Xr vfork 2
|
|
all signals, the signal mask, the signal stack,
|
|
and the restart/interrupt flags are inherited by the child.
|
|
.Pp
|
|
The
|
|
.Xr execve 2
|
|
system call reinstates the default
|
|
action for all signals which were caught and
|
|
resets all signals to be caught on the user stack.
|
|
Ignored signals remain ignored;
|
|
the signal mask remains the same;
|
|
signals that restart pending system calls continue to do so.
|
|
.Pp
|
|
The following is a list of all signals
|
|
with names as in the include file
|
|
.In signal.h :
|
|
.Bl -column SIGVTALARMXX "create core imagexxx"
|
|
.It Sy "NAME Default Action Description"
|
|
.It Dv SIGHUP No " terminate process" " terminal line hangup"
|
|
.It Dv SIGINT No " terminate process" " interrupt program"
|
|
.It Dv SIGQUIT No " create core image" " quit program"
|
|
.It Dv SIGILL No " create core image" " illegal instruction"
|
|
.It Dv SIGTRAP No " create core image" " trace trap"
|
|
.It Dv SIGABRT No " create core image" Ta Xr abort 3
|
|
call (formerly
|
|
.Dv SIGIOT )
|
|
.It Dv SIGEMT No " create core image" " emulate instruction executed"
|
|
.It Dv SIGFPE No " create core image" " floating-point exception"
|
|
.It Dv SIGKILL No " terminate process" " kill program"
|
|
.It Dv SIGBUS No " create core image" " bus error"
|
|
.It Dv SIGSEGV No " create core image" " segmentation violation"
|
|
.It Dv SIGSYS No " create core image" " non-existent system call invoked"
|
|
.It Dv SIGPIPE No " terminate process" " write on a pipe with no reader"
|
|
.It Dv SIGALRM No " terminate process" " real-time timer expired"
|
|
.It Dv SIGTERM No " terminate process" " software termination signal"
|
|
.It Dv SIGURG No " discard signal" " urgent condition present on socket"
|
|
.It Dv SIGSTOP No " stop process" " stop (cannot be caught or ignored)"
|
|
.It Dv SIGTSTP No " stop process" " stop signal generated from keyboard"
|
|
.It Dv SIGCONT No " discard signal" " continue after stop"
|
|
.It Dv SIGCHLD No " discard signal" " child status has changed"
|
|
.It Dv SIGTTIN No " stop process" " background read attempted from control terminal"
|
|
.It Dv SIGTTOU No " stop process" " background write attempted to control terminal"
|
|
.It Dv SIGIO No " discard signal" Tn " I/O"
|
|
is possible on a descriptor (see
|
|
.Xr fcntl 2 )
|
|
.It Dv SIGXCPU No " terminate process" " cpu time limit exceeded (see"
|
|
.Xr setrlimit 2 )
|
|
.It Dv SIGXFSZ No " terminate process" " file size limit exceeded (see"
|
|
.Xr setrlimit 2 )
|
|
.It Dv SIGVTALRM No " terminate process" " virtual time alarm (see"
|
|
.Xr setitimer 2 )
|
|
.It Dv SIGPROF No " terminate process" " profiling timer alarm (see"
|
|
.Xr setitimer 2 )
|
|
.It Dv SIGWINCH No " discard signal" " Window size change"
|
|
.It Dv SIGINFO No " discard signal" " status request from keyboard"
|
|
.It Dv SIGUSR1 No " terminate process" " User defined signal 1"
|
|
.It Dv SIGUSR2 No " terminate process" " User defined signal 2"
|
|
.El
|
|
.Sh NOTE
|
|
The
|
|
.Va sa_mask
|
|
field specified in
|
|
.Fa act
|
|
is not allowed to block
|
|
.Dv SIGKILL
|
|
or
|
|
.Dv SIGSTOP .
|
|
Any attempt to do so will be silently ignored.
|
|
.Pp
|
|
The following functions are either reentrant or not interruptible
|
|
by signals and are async-signal safe.
|
|
Therefore applications may
|
|
invoke them, without restriction, from signal-catching functions
|
|
or from a child process after calling
|
|
.Xr fork 2
|
|
in a multi-threaded process:
|
|
.Pp
|
|
Base Interfaces:
|
|
.Pp
|
|
.Fn _Exit ,
|
|
.Fn _exit ,
|
|
.Fn accept ,
|
|
.Fn access ,
|
|
.Fn alarm ,
|
|
.Fn bind ,
|
|
.Fn cfgetispeed ,
|
|
.Fn cfgetospeed ,
|
|
.Fn cfsetispeed ,
|
|
.Fn cfsetospeed ,
|
|
.Fn chdir ,
|
|
.Fn chmod ,
|
|
.Fn chown ,
|
|
.Fn close ,
|
|
.Fn connect ,
|
|
.Fn creat ,
|
|
.Fn dup ,
|
|
.Fn dup2 ,
|
|
.Fn execl ,
|
|
.Fn execle ,
|
|
.Fn execv ,
|
|
.Fn execve ,
|
|
.Fn faccessat ,
|
|
.Fn fchdir ,
|
|
.Fn fchmod ,
|
|
.Fn fchmodat ,
|
|
.Fn fchown ,
|
|
.Fn fchownat ,
|
|
.Fn fcntl ,
|
|
.Fn fork ,
|
|
.Fn fstat ,
|
|
.Fn fstatat ,
|
|
.Fn fsync ,
|
|
.Fn ftruncate ,
|
|
.Fn getegid ,
|
|
.Fn geteuid ,
|
|
.Fn getgid ,
|
|
.Fn getgroups ,
|
|
.Fn getpeername ,
|
|
.Fn getpgrp ,
|
|
.Fn getpid ,
|
|
.Fn getppid ,
|
|
.Fn getsockname ,
|
|
.Fn getsockopt ,
|
|
.Fn getuid ,
|
|
.Fn kill ,
|
|
.Fn link ,
|
|
.Fn linkat ,
|
|
.Fn listen ,
|
|
.Fn lseek ,
|
|
.Fn lstat ,
|
|
.Fn mkdir ,
|
|
.Fn mkdirat ,
|
|
.Fn mkfifo ,
|
|
.Fn mkfifoat ,
|
|
.Fn mknod ,
|
|
.Fn mknodat ,
|
|
.Fn open ,
|
|
.Fn openat ,
|
|
.Fn pause ,
|
|
.Fn pipe ,
|
|
.Fn poll ,
|
|
.Fn pselect ,
|
|
.Fn pthread_sigmask ,
|
|
.Fn raise ,
|
|
.Fn read ,
|
|
.Fn readlink ,
|
|
.Fn readlinkat ,
|
|
.Fn recv ,
|
|
.Fn recvfrom ,
|
|
.Fn recvmsg ,
|
|
.Fn rename ,
|
|
.Fn renameat ,
|
|
.Fn rmdir ,
|
|
.Fn select ,
|
|
.Fn send ,
|
|
.Fn sendmsg ,
|
|
.Fn sendto ,
|
|
.Fn setgid ,
|
|
.Fn setpgid ,
|
|
.Fn setsid ,
|
|
.Fn setsockopt ,
|
|
.Fn setuid ,
|
|
.Fn shutdown ,
|
|
.Fn sigaction ,
|
|
.Fn sigaddset ,
|
|
.Fn sigdelset ,
|
|
.Fn sigemptyset ,
|
|
.Fn sigfillset ,
|
|
.Fn sigismember ,
|
|
.Fn signal ,
|
|
.Fn sigpending ,
|
|
.Fn sigprocmask ,
|
|
.Fn sigsuspend ,
|
|
.Fn sleep ,
|
|
.Fn sockatmark ,
|
|
.Fn socket ,
|
|
.Fn socketpair ,
|
|
.Fn stat ,
|
|
.Fn symlink ,
|
|
.Fn symlinkat ,
|
|
.Fn tcdrain ,
|
|
.Fn tcflow ,
|
|
.Fn tcflush ,
|
|
.Fn tcgetattr ,
|
|
.Fn tcgetpgrp ,
|
|
.Fn tcsendbreak ,
|
|
.Fn tcsetattr ,
|
|
.Fn tcsetpgrp ,
|
|
.Fn time ,
|
|
.Fn times ,
|
|
.Fn umask ,
|
|
.Fn uname ,
|
|
.Fn unlink ,
|
|
.Fn unlinkat ,
|
|
.Fn utime ,
|
|
.Fn wait ,
|
|
.Fn waitpid ,
|
|
.Fn write .
|
|
.Pp
|
|
X/Open Systems Interfaces:
|
|
.Pp
|
|
.Fn sigpause ,
|
|
.Fn sigset ,
|
|
.Fn utimes .
|
|
.Pp
|
|
Realtime Interfaces:
|
|
.Pp
|
|
.Fn aio_error ,
|
|
.Fn clock_gettime ,
|
|
.Fn timer_getoverrun ,
|
|
.Fn aio_return ,
|
|
.Fn fdatasync ,
|
|
.Fn sigqueue ,
|
|
.Fn timer_gettime ,
|
|
.Fn aio_suspend ,
|
|
.Fn sem_post ,
|
|
.Fn timer_settime .
|
|
.Pp
|
|
Base Interfaces not specified as async-signal safe by
|
|
.Tn POSIX :
|
|
.Pp
|
|
.Fn fpathconf ,
|
|
.Fn pathconf ,
|
|
.Fn sysconf .
|
|
.Pp
|
|
Base Interfaces not specified as async-signal safe by
|
|
.Tn POSIX ,
|
|
but planned to be:
|
|
.Pp
|
|
.Fn ffs ,
|
|
.Fn htonl ,
|
|
.Fn htons ,
|
|
.Fn memccpy ,
|
|
.Fn memchr ,
|
|
.Fn memcmp ,
|
|
.Fn memcpy ,
|
|
.Fn memmove ,
|
|
.Fn memset ,
|
|
.Fn ntohl ,
|
|
.Fn ntohs ,
|
|
.Fn stpcpy ,
|
|
.Fn stpncpy ,
|
|
.Fn strcat ,
|
|
.Fn strchr ,
|
|
.Fn strcmp ,
|
|
.Fn strcpy ,
|
|
.Fn strcspn ,
|
|
.Fn strlen ,
|
|
.Fn strncat ,
|
|
.Fn strncmp ,
|
|
.Fn strncpy ,
|
|
.Fn strnlen ,
|
|
.Fn strpbrk ,
|
|
.Fn strrchr ,
|
|
.Fn strspn ,
|
|
.Fn strstr ,
|
|
.Fn strtok_r ,
|
|
.Fn wcpcpy ,
|
|
.Fn wcpncpy ,
|
|
.Fn wcscat ,
|
|
.Fn wcschr ,
|
|
.Fn wcscmp ,
|
|
.Fn wcscpy ,
|
|
.Fn wcscspn ,
|
|
.Fn wcslen ,
|
|
.Fn wcsncat ,
|
|
.Fn wcsncmp ,
|
|
.Fn wcsncpy ,
|
|
.Fn wcsnlen ,
|
|
.Fn wcspbrk ,
|
|
.Fn wcsrchr ,
|
|
.Fn wcsspn ,
|
|
.Fn wcsstr ,
|
|
.Fn wcstok ,
|
|
.Fn wmemchr ,
|
|
.Fn wmemcmp ,
|
|
.Fn wmemcpy ,
|
|
.Fn wmemmove ,
|
|
.Fn wmemset .
|
|
.Pp
|
|
Extension Interfaces:
|
|
.Pp
|
|
.Fn accept4 ,
|
|
.Fn bindat ,
|
|
.Fn closefrom ,
|
|
.Fn connectat ,
|
|
.Fn eaccess ,
|
|
.Fn ffsl ,
|
|
.Fn ffsll ,
|
|
.Fn flock ,
|
|
.Fn fls ,
|
|
.Fn flsl ,
|
|
.Fn flsll ,
|
|
.Fn futimesat ,
|
|
.Fn pipe2 ,
|
|
.Fn strlcat .
|
|
.Fn strlcpy ,
|
|
.Fn strsep .
|
|
.Pp
|
|
In addition, reading or writing
|
|
.Va errno
|
|
is async-signal safe.
|
|
.Pp
|
|
All functions not in the above lists are considered to be unsafe
|
|
with respect to signals.
|
|
That is to say, the behaviour of such
|
|
functions is undefined when they are called from a signal handler
|
|
that interrupted an unsafe function.
|
|
In general though, signal handlers should do little more than set a
|
|
flag; most other actions are not safe.
|
|
.Pp
|
|
Also, it is good practice to make a copy of the global variable
|
|
.Va errno
|
|
and restore it before returning from the signal handler.
|
|
This protects against the side effect of
|
|
.Va errno
|
|
being set by functions called from inside the signal handler.
|
|
.Sh RETURN VALUES
|
|
.Rv -std sigaction
|
|
.Sh EXAMPLES
|
|
There are three possible prototypes the handler may match:
|
|
.Bl -tag -offset indent -width short
|
|
.It Tn ANSI C :
|
|
.Ft void
|
|
.Fn handler int ;
|
|
.It Traditional BSD style:
|
|
.Ft void
|
|
.Fn handler int "int code" "struct sigcontext *scp" ;
|
|
.It Tn POSIX Dv SA_SIGINFO :
|
|
.Ft void
|
|
.Fn handler int "siginfo_t *info" "ucontext_t *uap" ;
|
|
.El
|
|
.Pp
|
|
The handler function should match the
|
|
.Dv SA_SIGINFO
|
|
prototype if the
|
|
.Dv SA_SIGINFO
|
|
bit is set in
|
|
.Va sa_flags .
|
|
It then should be pointed to by the
|
|
.Va sa_sigaction
|
|
member of
|
|
.Vt "struct sigaction" .
|
|
Note that you should not assign
|
|
.Dv SIG_DFL
|
|
or
|
|
.Dv SIG_IGN
|
|
this way.
|
|
.Pp
|
|
If the
|
|
.Dv SA_SIGINFO
|
|
flag is not set, the handler function should match
|
|
either the
|
|
.Tn ANSI C
|
|
or traditional
|
|
.Bx
|
|
prototype and be pointed to by
|
|
the
|
|
.Va sa_handler
|
|
member of
|
|
.Vt "struct sigaction" .
|
|
In practice,
|
|
.Fx
|
|
always sends the three arguments of the latter and since the
|
|
.Tn ANSI C
|
|
prototype is a subset, both will work.
|
|
The
|
|
.Va sa_handler
|
|
member declaration in
|
|
.Fx
|
|
include files is that of
|
|
.Tn ANSI C
|
|
(as required by
|
|
.Tn POSIX ) ,
|
|
so a function pointer of a
|
|
.Bx Ns -style
|
|
function needs to be casted to
|
|
compile without warning.
|
|
The traditional
|
|
.Bx
|
|
style is not portable and since its capabilities
|
|
are a full subset of a
|
|
.Dv SA_SIGINFO
|
|
handler,
|
|
its use is deprecated.
|
|
.Pp
|
|
The
|
|
.Fa sig
|
|
argument is the signal number, one of the
|
|
.Dv SIG...
|
|
values from
|
|
.In signal.h .
|
|
.Pp
|
|
The
|
|
.Fa code
|
|
argument of the
|
|
.Bx Ns -style
|
|
handler and the
|
|
.Va si_code
|
|
member of the
|
|
.Fa info
|
|
argument to a
|
|
.Dv SA_SIGINFO
|
|
handler contain a numeric code explaining the
|
|
cause of the signal, usually one of the
|
|
.Dv SI_...
|
|
values from
|
|
.In sys/signal.h
|
|
or codes specific to a signal, i.e., one of the
|
|
.Dv FPE_...
|
|
values for
|
|
.Dv SIGFPE .
|
|
.Pp
|
|
The
|
|
.Fa scp
|
|
argument to a
|
|
.Bx Ns -style
|
|
handler points to an instance of
|
|
.Vt "struct sigcontext" .
|
|
.Pp
|
|
The
|
|
.Fa uap
|
|
argument to a
|
|
.Tn POSIX
|
|
.Dv SA_SIGINFO
|
|
handler points to an instance of
|
|
ucontext_t.
|
|
.Sh ERRORS
|
|
The
|
|
.Fn sigaction
|
|
system call
|
|
will fail and no new signal handler will be installed if one
|
|
of the following occurs:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EINVAL
|
|
The
|
|
.Fa sig
|
|
argument
|
|
is not a valid signal number.
|
|
.It Bq Er EINVAL
|
|
An attempt is made to ignore or supply a handler for
|
|
.Dv SIGKILL
|
|
or
|
|
.Dv SIGSTOP .
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr kill 1 ,
|
|
.Xr kill 2 ,
|
|
.Xr ptrace 2 ,
|
|
.Xr sigaltstack 2 ,
|
|
.Xr sigpending 2 ,
|
|
.Xr sigprocmask 2 ,
|
|
.Xr sigsuspend 2 ,
|
|
.Xr wait 2 ,
|
|
.Xr fpsetmask 3 ,
|
|
.Xr setjmp 3 ,
|
|
.Xr siginfo 3 ,
|
|
.Xr siginterrupt 3 ,
|
|
.Xr sigsetops 3 ,
|
|
.Xr ucontext 3 ,
|
|
.Xr tty 4
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn sigaction
|
|
system call is expected to conform to
|
|
.St -p1003.1-90 .
|
|
The
|
|
.Dv SA_ONSTACK
|
|
and
|
|
.Dv SA_RESTART
|
|
flags are Berkeley extensions,
|
|
as are the signals,
|
|
.Dv SIGTRAP ,
|
|
.Dv SIGEMT ,
|
|
.Dv SIGBUS ,
|
|
.Dv SIGSYS ,
|
|
.Dv SIGURG ,
|
|
.Dv SIGIO ,
|
|
.Dv SIGXCPU ,
|
|
.Dv SIGXFSZ ,
|
|
.Dv SIGVTALRM ,
|
|
.Dv SIGPROF ,
|
|
.Dv SIGWINCH ,
|
|
and
|
|
.Dv SIGINFO .
|
|
Those signals are available on most
|
|
.Bx Ns \-derived
|
|
systems.
|
|
The
|
|
.Dv SA_NODEFER
|
|
and
|
|
.Dv SA_RESETHAND
|
|
flags are intended for backwards compatibility with other operating
|
|
systems.
|
|
The
|
|
.Dv SA_NOCLDSTOP ,
|
|
and
|
|
.Dv SA_NOCLDWAIT
|
|
.\" and
|
|
.\" SA_SIGINFO
|
|
flags are featuring options commonly found in other operating systems.
|
|
The flags are approved by
|
|
.St -susv2 ,
|
|
along with the option to avoid zombie creation by ignoring
|
|
.Dv SIGCHLD .
|