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manual: Update signal descriptions 

Based on auditing all the signals and source trees for Hurd and
Linux...

SIGSYS - This is not used for a bad system call (ENOSYS is used
for that).  This is used by SECCOMP and some cases where an invalid
sub-function was requested.

SIGSTKFLT - Note it used to be a coprocessor stack fault but is now
obsolete and available for general user use.

SIGLOST - Hurd only now; note that its original purpose as an NFS
lock lost signal is obsolete.

SIGPWR - Note this is for power lost *and* power restored, and is
more a user-mode signal than a kernel-generated signal.

Reviewed-by: Florian Weimer <fweimer@redhat.com>
This commit is contained in:
DJ Delorie 2025-01-17 17:34:02 -05:00
parent cdb0800022
commit bb6496b964
1 changed files with 28 additions and 9 deletions
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37
manual/signal.texi
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@ -427,9 +427,18 @@ failure to properly emulate them.
@deftypevr Macro int SIGSYS
@standards{Unix, signal.h}
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.
System call event. This signal may be generated by a valid system
call which requested an invalid sub-function, and also by the SECCOMP
filter when it filters or traps a system call.
If the system call itself is invalid or unsupported by the kernel, the
call will not raise this signal, but will return @code{ENOSYS}.
@end deftypevr
@deftypevr Macro int SIGSTKFLT
Coprocessor stack fault. Obsolete, no longer generated. This signal
may be used by applications in much the way @code{SIGUSR1} and
@code{SIGUSR2} are.
@end deftypevr
@node Termination Signals
@ -752,12 +761,11 @@ that isn't connected. @xref{Sending Data}.
@deftypevr Macro int SIGLOST
@standards{GNU, signal.h}
@cindex lost resource signal
Resource lost. This signal is generated when you have an advisory lock
on an NFS file, and the NFS server reboots and forgets about your lock.
On @gnuhurdsystems{}, @code{SIGLOST} is generated when any server program
dies unexpectedly. It is usually fine to ignore the signal; whatever
call was made to the server that died just returns an error.
Resource lost. On @gnuhurdsystems{}, @code{SIGLOST} is generated when
any server program dies unexpectedly. It is usually fine to ignore
the signal; whatever call was made to the server that died just
returns an error. This signal's original purpose of signalling a lost
NFS lock is obsolete.
@end deftypevr
@deftypevr Macro int SIGXCPU
@ -817,6 +825,17 @@ to print some status information about the system and what the process
is doing. Otherwise the default is to do nothing.
@end deftypevr
@deftypevr Macro int SIGPWR
@cindex power event signal
Power lost or restored. On s390x Linux systems, this signal is
generated when a machine check warning is issued, and is sent to the
process designated to receive ctrl-alt-del notifications. Otherwise,
it is up to userspace applications to generate this signal and manage
notifications as to the type of power event that happened.
The default action is to terminate the process.
@end deftypevr
@node Signal Messages
@subsection Signal Messages
@cindex signal messages