Module Name: src
Committed By: dholland
Date: Sat Jul 9 23:12:27 UTC 2016
Modified Files:
src/share/man/man7: signal.7
Log Message:
Document all the signals properly. Please review.
Kick out the list of async-signal-safe functions (it is now in
sigaction(2)) because this is not a programmer-facing document.
XXX: if anyone knows definitively whether SIGEMT is actually used by
XXX: anything, please update the weasel words I put in.
To generate a diff of this commit:
cvs rdiff -u -r1.17 -r1.18 src/share/man/man7/signal.7
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/share/man/man7/signal.7
diff -u src/share/man/man7/signal.7:1.17 src/share/man/man7/signal.7:1.18
--- src/share/man/man7/signal.7:1.17 Sat Jul 19 14:53:22 2014
+++ src/share/man/man7/signal.7 Sat Jul 9 23:12:27 2016
@@ -1,4 +1,4 @@
-.\" $NetBSD: signal.7,v 1.17 2014/07/19 14:53:22 roy Exp $
+.\" $NetBSD: signal.7,v 1.18 2016/07/09 23:12:27 dholland Exp $
.\"
.\" Copyright (c) 1999 The NetBSD Foundation, Inc.
.\" All rights reserved.
@@ -24,213 +24,569 @@
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
-.Dd July 18, 2014
+.Dd July 9, 2016
.Dt SIGNAL 7
.Os
.Sh NAME
.Nm signal
.Nd signal facilities
.Sh DESCRIPTION
-The
-.In signal.h
-header file defines the following signals:
+A
+.Nm
+is a system-level notification delivered to a process.
+Signals may be generated as the result of process activity, by certain
+user inputs, by kernel facilities or subsystems, or sent
+programmatically by other processes or by users.
+There is a small fixed set of signals, each with a symbolic name and a
+number.
+For historical reasons many of the numbers are ``well-known values'',
+which are in practice the same on all implementations and
+realistically can never be changed.
+(Nonetheless, compiled code should always use only the symbolic
+names.)
+Many/most signals also have specific semantics, both in how they can
+be generated and in their effects.
+Some are special cases in ways that have quite far-reaching
+consequences.
+.Pp
+When a signal is
+.Em posted
+.Pq Dq sent
+to a process, in general any of several things can happen.
+If the process has elected to
+.Em ignore
+the signal, it is discarded and nothing happens.
+(Some signals may not be ignored, however.)
+If the process has elected to
+.Em block
+the signal temporarily, delivery is postponed until the process
+later unblocks that signal.
+Otherwise, the signal is
+.Em delivered,
+meaning that whatever the process is doing is interrupted in order to
+react to the signal.
+(Note that processes that are waiting in the kernel must unwind what
+they are doing for signals to be delivered.
+This can sometimes be expensive.
+See
+.Xr sigaction 2
+for further information.)
+.Pp
+If the process has elected to
+.Em catch
+the signal, which means that the process has installed a handler to
+react to the signal in some process-specific way, the kernel arranges
+for the process's handler logic to be invoked.
+This is always done in a way that allows the process to resume if
+desired.
+(Note, however, that some signals may not be caught.)
+Otherwise, the default action for the signal is taken.
+For most signals the default action is a core dump.
+See the table below.
+Note that the term
+.Em delivery
+is also used for the specific process of arranging for a signal
+handler to be invoked.
+.Pp
+In general, signals are delivered as soon as they are posted.
+(Some delays may occur due to scheduling.)
+However, in some cases a process that has been sleeping in the kernel
+may need to do slow things as part of unwinding its state; this can
+sometimes lead to human-perceptible delays.
+.Pp
+Also, some sleep states within the kernel are
+.Em uninterruptible
+meaning that signals posted will have no effect until the state
+clears.
+These states are supposed to be short-term only, but sometimes kernel
+bugs make this not the case and one can end up with unkillable
+processes.
+Such processes appear in state "D" in
+.Xr ps 1 .
+In general the only way to get rid of them is to reboot.
+(However, when the "wchan" reported is "tstile", it means the process
+is waiting for some other process to release resources; sometimes if
+one can find and kill that process the situation is recoverable.)
+.Ss Signal list
+The following signals are defined in
+.Nx :
.Pp
-.Bl -column ".Sy Value" ".Dv SIGVTALARM" "terminate process" -compact
-.It Sy "Value" Ta Sy "Name" Ta Sy "Default Action" Ta Sy "Description"
-.It 1 Ta Dv SIGHUP Ta "terminate process" Ta "terminal line hangup"
-.It 2 Ta Dv SIGINT Ta "terminate process" Ta "interrupt program"
-.It 3 Ta Dv SIGQUIT Ta "create core image" Ta "quit program"
-.It 4 Ta Dv SIGILL Ta "create core image" Ta "illegal instruction"
-.It 5 Ta Dv SIGTRAP Ta "create core image" Ta "trace trap"
-.It 6 Ta Dv SIGABRT Ta "create core image" Ta Xr abort 3
-call (formerly
-.Dv SIGIOT )
-.It 7 Ta Dv SIGEMT Ta "create core image" Ta "emulate instruction executed"
-.It 8 Ta Dv SIGFPE Ta "create core image" Ta "floating-point exception"
-.It 9 Ta Dv SIGKILL Ta "terminate process" Ta "kill program (cannot be caught or ignored)"
-.It 10 Ta Dv SIGBUS Ta "create core image" Ta "bus error"
-.It 11 Ta Dv SIGSEGV Ta "create core image" Ta "segmentation violation"
-.It 12 Ta Dv SIGSYS Ta "create core image" Ta "invalid system call argument"
-.It 13 Ta Dv SIGPIPE Ta "terminate process" Ta "write to a pipe with no reader"
-.It 14 Ta Dv SIGALRM Ta "terminate process" Ta "real-time timer expired"
-.It 15 Ta Dv SIGTERM Ta "terminate process" Ta "software termination signal"
-.It 16 Ta Dv SIGURG Ta "discard signal" Ta "urgent condition present on socket"
-.It 17 Ta Dv SIGSTOP Ta "stop process" Ta "stop (cannot be caught or ignored)"
-.It 18 Ta Dv SIGTSTP Ta "stop process" Ta "stop signal generated from keyboard"
-.It 19 Ta Dv SIGCONT Ta "discard signal" Ta "continue after stop (even if blocked or ignored)"
-.It 20 Ta Dv SIGCHLD Ta "discard signal" Ta "child status has changed"
-.It 21 Ta Dv SIGTTIN Ta "stop process" Ta "background read attempted from control terminal"
-.It 22 Ta Dv SIGTTOU Ta "stop process" Ta "background write attempted to control terminal"
-.It 23 Ta Dv SIGIO Ta "discard signal" Ta "I/O is possible on a descriptor (see"
-.Xr fcntl 2 )
-.It 24 Ta Dv SIGXCPU Ta "terminate process" Ta "CPU time limit exceeded (see"
-.Xr setrlimit 2 )
-.It 25 Ta Dv SIGXFSZ Ta "terminate process" Ta "file size limit exceeded (see"
-.Xr setrlimit 2 )
-.It 26 Ta Dv SIGVTALRM Ta "terminate process" Ta "virtual time alarm (see"
-.Xr setitimer 2 )
-.It 27 Ta Dv SIGPROF Ta "terminate process" Ta "profiling timer alarm (see"
-.Xr setitimer 2 )
-.It 28 Ta Dv SIGWINCH Ta "discard signal" Ta "window size change"
-.It 29 Ta Dv SIGINFO Ta "discard signal" Ta "status request from keyboard"
-.It 30 Ta Dv SIGUSR1 Ta "terminate process" Ta "user-defined signal 1"
-.It 31 Ta Dv SIGUSR2 Ta "terminate process" Ta "user-defined signal 2"
-.It 32 Ta Dv SIGPWR Ta "discard signal" Ta "power failure/restart"
+.Bl -column ".Sy SIGVTALRM" "Profiling timer expired blablabla" -compact
+.\".It Sy "Symbol" Ta Sy "Descriptive name"
+.It Dv SIGHUP Ta "Hangup"
+.It Dv SIGINT Ta "Interrupt"
+.It Dv SIGQUIT Ta "Quit"
+.It Dv SIGILL Ta "Illegal instruction"
+.It Dv SIGTRAP Ta "Trace/BPT trap"
+.It Dv SIGABRT Ta "Abort trap"
+.It Dv SIGEMT Ta "EMT trap"
+.It Dv SIGFPE Ta "Floating point exception"
+.It Dv SIGKILL Ta "Killed"
+.It Dv SIGBUS Ta "Bus error"
+.It Dv SIGSEGV Ta "Segmentation fault"
+.It Dv SIGSYS Ta "Bad system call"
+.It Dv SIGPIPE Ta "Broken pipe"
+.It Dv SIGALRM Ta "Alarm clock"
+.It Dv SIGTERM Ta "Terminated"
+.It Dv SIGURG Ta "Urgent I/O condition"
+.It Dv SIGSTOP Ta "Suspended (signal)"
+.It Dv SIGTSTP Ta "Suspended"
+.It Dv SIGCONT Ta "Continued"
+.It Dv SIGCHLD Ta "Child exited"
+.It Dv SIGTTIN Ta "Stopped (tty input)"
+.It Dv SIGTTOU Ta "Stopped (tty output)"
+.It Dv SIGIO Ta "I/O possible"
+.It Dv SIGXCPU Ta "CPU time limit exceeded"
+.It Dv SIGXFSZ Ta "File size limit exceeded"
+.It Dv SIGVTALRM Ta "Virtual timer expired"
+.It Dv SIGPROF Ta "Profiling timer expired"
+.It Dv SIGWINCH Ta "Window size changed"
+.It Dv SIGINFO Ta "Information request"
+.It Dv SIGUSR1 Ta "User defined signal 1"
+.It Dv SIGUSR2 Ta "User defined signal 2"
+.It Dv SIGPWR Ta "Power fail/restart"
.El
.Pp
-A function that is async-signal-safe is either reentrant or
-non-interruptible by signals.
-This means that they can be used in
-signal handlers
-and in the child of threaded programs after doing
-.Xr fork 2 .
+These are numbered 1 to 32.
+(There is no signal 0; 0 is a reserved value that can be used as a
+no-op with some signal operations.)
.Pp
-The following functions are async-signal-safe.
-Any function not listed
-below is unsafe to use in signal handlers.
+Detailed descriptions of these signals follow.
.Pp
-.Xr _Exit 2 ,
-.Xr _exit 2 ,
-.Xr abort 3 ,
-.Xr accept 2 ,
-.Xr access 2 ,
-.\" .Xr aio_error
-.\" .Xr aio_return
-.\" .Xr aio_suspend
+.Bl -tag -width "aaa"
+.\" ************
+.It Dv SIGHUP (Hangup)
+This signal is generated by the tty driver
+.Xr tty 4
+to indicate a hangup condition on a process's controlling terminal:
+the user has disconnected.
+Accordingly, the default action is to terminate the process.
+This signal is also used by many daemons,
+such as
+.Xr inetd 8 ,
+as a cue to reload configuration.
+The number for
+.Dv SIGHUP
+is 1, which is quite well known.
+.\" ************
+.It Dv SIGINT (Interrupt)
+This signal is generated by the tty driver
+.Xr tty 4
+when the user presses the interrupt character, normally control-C.
+The default action is to terminate the process.
+The number for
+.Dv SIGINT
+is 2.
+.\" ************
+.It Dv SIGQUIT Ta (Quit)
+This signal is generated by the tty driver
+.Xr tty 4
+when the user presses the quit character, normally control-backspace.
+The default action is to terminate the process and dump core.
+The number for
+.Dv SIGQUIT
+is 3.
+.\" ************
+.It Dv SIGILL Ta (Illegal instruction)
+This signal is generated synchronously by the kernel when the process
+executes an invalid instruction.
+The default action is to terminate the process and dump core.
+Note: the results of executing an illegal instruction when
+.Dv SIGILL
+is blocked or ignored are formally unspecified.
+The number for
+.Dv SIGILL
+is 4.
+.\" ************
+.It Dv SIGTRAP Ta (Trace/BPT trap)
+This signal is used when a process is being traced
+(see
+.Xr ptrace 2 )
+to indicate that the process has stopped at a breakpoint or after
+single-stepping.
+It is normally intercepted by the debugger and not exposed to the
+debuggee.
+The default action is to terminate the process and dump core.
+The number for
+.Dv SIGTRAP
+is 5.
+.\" ************
+.It Dv SIGABRT Ta (Abort trap)
+This signal is generated when the
+.Xr abort 3
+standard library function is called.
+The default action is to terminate the process and dump core.
+The number for
+.Dv SIGABRT
+is 6.
+This number was also formerly used for
+.Dv SIGIOT ,
+which is no longer defined.
+.\" ************
+.It Dv SIGEMT Ta (EMT trap)
+In theory this signal is generated when an instruction needs to be
+emulated.
+.\" XXX expand this -- I don't know, grep isn't helping much and
+.\" information seems pretty thin on the ground on the net.
+The default action is to terminate the process and dump core.
+The number for
+.Dv SIGEMT
+is 7.
+.\" ************
+.It Dv SIGFPE Ta (Floating point exception)
+This signal is generated when an invalid floating point operation is
+detected by hardware or by a soft-float library.
+The default action is to terminate the process and dump core.
+The number for
+.Dv SIGFPE
+is 8.
+.\" ************
+.It Dv SIGKILL Ta (Killed)
+This signal cannot be caught or ignored.
+The (unconditional) action is to terminate the process.
+It is most often sent by system administrators, but is also generated
+by the kernel in response to running completely out of memory and
+swap space.
+Note that because many processes need to perform cleanup before
+exiting, it is usually best (as a user or administrator) to not deploy
+.Dv SIGKILL
+until a process has failed to respond to other signals.
+The number for
+.Dv SIGKILL
+is 9, which is extremely well known.
+.\" ************
+.It Dv SIGBUS Ta (Bus error)
+This signal is generated synchronously by the kernel when the process
+performs certain kinds of invalid memory accesses.
+The most common cause of
+.Dv SIGBUS
+is an unaligned memory access; however, on some architectures it may
+cover other memory conditions, such as attempts to access memory
+belonging to the kernel.
+The default action is to terminate the process and dump core.
+Note: the results of performing such invalid accesses when
+.Dv SIGBUS
+is blocked or ignored are formally unspecified.
+The number for
+.Dv SIGBUS
+is 10.
+.\" ************
+.It Dv SIGSEGV Ta (Segmentation fault)
+This signal is generated synchronously by the kernel when the process
+attempts to access unmapped memory, or access memory in a manner that
+the protection settings for that memory region do not permit.
+On some architectures other assorted permission or protection errors
+also yield
+.Dv SIGSEGV .
+On
+.Nx ,
+passing invalid pointers to system calls will yield failure with
+.Er EFAULT
+but not also
+.Dv SIGSEGV .
+The default action is to terminate the process and dump core.
+Note: the results of an invalid memory access when
+.Dv SIGSEGV
+is blocked or ignored are formally unspecified.
+The number for
+.Dv SIGSEGV
+is 11, which is very well known.
+.\" ************
+.It Dv SIGSYS Ta (Bad system call)
+This signal is generated by the kernel, in addition to failing with
+.Er ENOSYS ,
+when a system call is made using an invalid system call number.
+.\" (This facility was intended to facilitate emulation of system calls.)
+The default action is to terminate the process and dump core.
+The number for
+.Dv SIGSYS
+is 12.
+.\" ************
+.It Dv SIGPIPE Ta (Broken pipe)
+This signal is generated by the kernel, in addition to failing with
+.Er EPIPE ,
+when a
+.Xr write 2
+call or similar is made on a pipe or socket that has been closed and
+has no readers.
+The default action is to terminate the process.
+The number for
+.Dv SIGPIPE
+is 13.
+.\" ************
+.It Dv SIGALRM Ta (Alarm clock)
+This signal is generated by the kernel when a real-time timer expires.
+See
.Xr alarm 3 ,
-.Xr bind 2 ,
-.Xr cfgetispeed 3 ,
-.Xr cfgetospeed 3 ,
-.Xr cfsetispeed 3 ,
-.Xr cfsetospeed 3 ,
-.Xr chdir 2 ,
-.Xr chmod 2 ,
-.Xr chown 2 ,
-.Xr clock_gettime 2 ,
-.Xr close 2 ,
-.Xr connect 2 ,
-.Xr creat 3 ,
-.Xr dup 2 ,
-.Xr dup2 2 ,
-.Xr execle 3 ,
-.Xr execve 2 ,
-.Xr fchmod 2 ,
-.Xr fchown 2 ,
-.Xr fcntl 2 ,
-.Xr fdatasync 2 ,
-.Xr fork 2 ,
-.Xr fpathconf 2 ,
-.Xr fstat 2 ,
-.Xr fsync 2 ,
-.Xr ftruncate 2 ,
-.Xr getegid 2 ,
-.Xr geteuid 2 ,
-.Xr getgid 2 ,
-.Xr getgroups 2 ,
-.Xr getpeername 2 ,
-.Xr getpgrp 2 ,
-.Xr getpid 2 ,
-.Xr getppid 2 ,
-.Xr getsockname 2 ,
-.Xr getsockopt 2 ,
-.Xr getuid 2 ,
-.Xr kill 2 ,
-.Xr link 2 ,
-.Xr listen 2 ,
-.Xr lseek 2 ,
-.Xr lstat 2 ,
-.Xr mkdir 2 ,
-.Xr mkfifo 2 ,
-.Xr open 2 ,
-.Xr pathconf 2 ,
-.Xr pause 3 ,
-.Xr pipe 2 ,
-.Xr poll 2 ,
-.\" .Xr posix_trace_event 2
-.\" .Xr pselect 2
-.Xr pthread_mutex_unlock 3 ,
-.Xr raise 3 ,
-.Xr read 2 ,
-.Xr readlink 2 ,
-.Xr recv 2 ,
-.Xr recvfrom 2 ,
-.Xr recvmsg 2 ,
-.Xr rename 2 ,
-.Xr rmdir 2 ,
-.Xr select 2 ,
-.Xr sem_post 3 ,
-.Xr send 2 ,
-.Xr sendmsg 2 ,
-.Xr sendto 2 ,
-.Xr setgid 2 ,
-.Xr setpgid 2 ,
-.Xr setsid 2 ,
-.Xr setsockopt 2 ,
-.Xr setuid 2 ,
-.Xr shutdown 2 ,
-.Xr sigaction 2 ,
-.Xr sigaddset 3 ,
-.Xr sigdelset 3 ,
-.Xr sigemptyset 3 ,
-.Xr sigfillset 3 ,
-.Xr sigismember 3 ,
-.Xr sleep 3 ,
-.Xr signal 3 ,
-.Xr sigpause 3 ,
-.Xr sigpending 2 ,
-.Xr sigprocmask 2 ,
-.\" .Xr sigqueue
-.Xr sigset 3 ,
-.Xr sigsuspend 2 ,
-.Xr sockatmark 3 ,
-.Xr socket 2 ,
-.Xr socketpair 2 ,
-.Xr stat 2 ,
-.Xr symlink 2 ,
-.Xr sysconf 3 ,
-.Xr tcdrain 3 ,
-.Xr tcflow 3 ,
-.Xr tcflush 3 ,
-.Xr tcgetattr 3 ,
-.Xr tcgetpgrp 3 ,
-.Xr tcsendbreak 3 ,
-.Xr tcsetattr 3 ,
-.Xr tcsetpgrp 3 ,
-.Xr time 3 ,
-.Xr timer_getoverrun 2 ,
-.Xr timer_gettime 2 ,
-.Xr timer_settime 2 ,
-.Xr times 3 ,
-.Xr umask 2 ,
-.Xr uname 3 ,
-.Xr unlink 2 ,
-.Xr utime 3 ,
-.Xr wait 2 ,
-.Xr waitpid 2 ,
-.Xr write 2 .
-.Sh SEE ALSO
-.Xr kill 1 ,
-.Xr kill 2 ,
-.Xr ptrace 2 ,
-.Xr sigaction 2 ,
-.Xr sigaltstack 2 ,
-.Xr sigprocmask 2 ,
-.Xr sigstack 2 ,
-.Xr sigsuspend 2 ,
-.Xr fpgetmask 3 ,
-.Xr fpsetmask 3 ,
-.Xr setjmp 3 ,
-.Xr sigblock 3 ,
-.Xr siginterrupt 3 ,
-.Xr signal 3 ,
-.Xr sigpause 3 ,
-.Xr sigsetmask 3 ,
-.Xr sigsetops 3 ,
+.Xr setitimer 2 ,
+and
+.Xr timer_settime 2 .
+The default action is to terminate the process.
+The number for
+.Dv SIGALRM
+is 14.
+.\" ************
+.It Dv SIGTERM Ta (Terminated)
+This signal is the default signal sent by
+.Xr kill 1
+and represents a user or administrator request that a program shut
+down.
+It is sent to all processes as part of the
+.Xr shutdown 8
+procedure.
+The default action is to terminate the process.
+The number for
+.Dv SIGTERM
+is 15.
+.\" ************
+.It Dv SIGURG Ta (Urgent I/O condition)
+This signal is generated when an ``urgent condition'' exists on a
+socket.
+In practice this means when
+.Xr tcp 4
+out-of-band data has arrived.
+The default action is to do nothing.
+The number for
+.Dv SIGURG
+is 16.
+.\" ************
+.It Dv SIGSTOP Ta (Suspended (signal))
+This signal cannot be caught or ignored.
+The (unconditional) action is to stop the process.
+Note that like with
+.Dv SIGKILL
+(and for similar reasons) it is best to not send this signal until a
+process has failed to respond to
+.Dv SIGTSTP .
+It can also be used by processes to stop themselves after catching
+.Dv SIGTSTP .
+A process that is explicitly stopped will not run again until told to
+with
+.Dv SIGCONT .
+The number for
+.Dv SIGSTOP
+is 17.
+.\" ************
+.It Dv SIGTSTP Ta (Suspended)
+This signal is generated by the tty driver
+.Xr tty 4
+when the user presses the stop character, normally control-Z.
+The default action is to stop the process.
+The number for
+.Dv SIGTSTP
+is 18.
+.\" ************
+.It Dv SIGCONT Ta (Continued)
+This signal is generated by the job-control feature of shells to
+manage processes.
+It causes the target process to start executing again after previously
+being stopped.
+This happens as a magic extra effect
+.Nm before
+the signal is actually delivered.
+The default action when the signal is delivered is to do nothing (else).
+The number for
+.Dv SIGCONT
+is 19.
+.\" ************
+.It Dv SIGCHLD Ta (Child exited)
+This signal is generated by the kernel when one of a process's
+immediate children exits and can be waited for using one of the
+.Xr wait 3
+family of functions.
+The default action is to do nothing.
+As a special case hack, if
+.Dv SIGCHLD
+is ignored (not merely blocked) when a process is
+.Em created ,
+it is detached from its parent immediately so it need not be waited
+for.
+This behavior is a System V historic wart, implemented in
+.Nx
+only for compatibility.
+It is not portable, not recommended, and should not be used by new
+code.
+.\" XXX should refer to something that can be used by new code...
+The number for
+.Dv SIGCHLD
+is 20.
+This signal was spelled
+.Dv SIGCLD
+in old System V versions and today many systems provide both
+spellings.
+.\" ************
+.It Dv SIGTTIN Ta (Stopped (tty input))
+This signal is generated by the tty driver
.Xr tty 4
+when a process that is not in the foreground of its controlling
+terminal attempts to read from this terminal.
+The default action is to stop the process.
+The number for
+.Dv SIGTTIN
+is 21.
+.\" ************
+.It Dv SIGTTOU Ta (Stopped (tty output))
+This signal is generated by the tty driver
+.Xr tty 4
+when a process that is not in the foreground of its controlling
+terminal attempts to write to this terminal, if the terminal is
+configured accordingly, which is not the default.
+(See
+.Xr termios 4 .)
+The default action is to stop the process.
+The number for
+.Dv SIGTTOU
+is 22.
+.\" ************
+.It Dv SIGIO Ta (I/O possible)
+This signal is sent by the kernel when I/O becomes possible on a file
+handle opened for asynchronous access with
+.Dv O_ASYNC .
+See
+.Xr open 2
+and
+.Xr fcntl 2 .
+The default action is to do nothing.
+The number for
+.Dv SIGIO
+is 23.
+.\" ************
+.It Dv SIGXCPU Ta (CPU time limit exceeded)
+This signal is sent by the kernel when the amount of CPU time consumed
+exceeds the configured limit.
+See
+.Xr setrlimit 2
+and the
+ulimit
+and
+rlimit
+builtins of
+.Xr sh 1
+and
+.Xr csh 1
+respectively.
+The default action is to terminate the process.
+The number for
+.Dv SIGXCPU
+is 24.
+.\" ************
+.It Dv SIGXFSZ Ta (File size limit exceeded)
+This signal is sent by the kernel when a write causes the size of a
+file to exceed the configured limit.
+See
+.Xr setrlimit 2
+and the
+ulimit
+and
+rlimit
+builtins of
+.Xr sh 1
+and
+.Xr csh 1
+respectively.
+The default action is to terminate the process.
+The number for
+.Dv SIGXFSZ
+is 25.
+.\" ************
+.It Dv SIGVTALRM Ta (Virtual timer expired)
+This signal is generated by the kernel when a virtual-time (process
+execution time) timer expires.
+See
+.Xr setitimer 2
+and
+.Xr timer_settime 2 .
+The default action is to terminate the process.
+The number for
+.Dv SIGVTALRM
+is 26.
+.\" ************
+.It Dv SIGPROF Ta (Profiling timer expired)
+This signal is generated by the kernel when a profiling timer
+expires.
+See
+.Xr setitimer 2
+and
+.Xr timer_settime 2 .
+The default action is to terminate the process.
+The number for
+.Dv SIGPROF
+is 27.
+.\" ************
+.It Dv SIGWINCH Ta (Window size changed)
+This signal is generated by the tty driver
+.Xr tty 4
+when the stored window size of the process's controlling terminal has
+changed.
+The default action is to do nothing.
+The number for
+.Dv SIGWINCH
+is 28.
+.\" ************
+.It Dv SIGINFO Ta (Information request)
+This signal is generated by the tty driver
+.Xr tty 4
+when the user presses the status request character, normally
+control-T.
+The default action is to do nothing.
+The number for
+.Dv SIGINFO
+is 29.
+.\" ************
+.It Dv SIGUSR1 Ta (User defined signal 1)
+This signal is not generated by the system and is made available for
+applications to use for their own purposes.
+Many daemons use it for restart or reload requests of various types.
+The default action is to terminate the process.
+The number for
+.Dv SIGUSR1
+is 30.
+.\" ************
+.It Dv SIGUSR2 Ta (User defined signal 2)
+This signal is not generated by the system and is made available for
+applications to use for their own purposes.
+The default action is to terminate the process.
+The number for
+.Dv SIGUSR2
+is 31.
+.\" ************
+.It Dv SIGPWR Ta (Power fail/restart)
+This signal is notionally sent by the kernel or by a privileged
+monitor process when an external power failure is detected, and again
+when power has been restored.
+Currently
+.Nx
+does not in fact send
+.Dv SIGPWR ,
+although it is possible to prepare a custom configuration for
+.Xr powerd 8
+that does so.
+The default action is to do nothing.
+The number for
+.Dv SIGPWR
+is 32.
+.\" ************
+.Ss Shell Interface
+Signals may be sent with the
+.Xr kill 1
+utility, either by number or the symbolic name without the ``SIG'' part.
+This utility is built into many shells to allow addressing job control
+jobs.
+.Ss Program Interface
+In C code signals may be sent using
+.Xr raise 3,
+.Xr kill 2,
+.Xr pthread_kill 2,
+and some other related functions.
+.Pp
+Signals may be caught or ignored using
+.Xr sigaction 2
+or the simpler
+.Xr signal 3 ,
+and blocked using
+.Xr sigprocmask .
.Sh STANDARDS
-These signals conform to
-.St -p1003.1-90 ,
-with the exception of
+The
.Dv SIGTRAP ,
.Dv SIGEMT ,
.Dv SIGBUS ,
@@ -244,18 +600,16 @@ with the exception of
.Dv SIGWINCH ,
and
.Dv SIGINFO
-which are Berkeley extensions (available on most
+signals are long-existing Berkeley extensions, available on most
.Bx Ns \-derived
-systems), and
+systems.
+The
.Dv SIGPWR
-which comes from System V.
+signal comes from System V.
+.Pp
+The remaining signals conform to
+.St -p1003.1-90 .
.Sh HISTORY
.Dv SIGPWR
was introduced in
.Nx 1.4 .
-.Sh NOTES
-The current
-.Nx
-kernel never generates the
-.Dv SIGPWR
-signal.
