The psignal
function shall
display a message on the stderr stream.
If s is not the null pointer, and does
not point to an empty string (e.g. "\0"), the
message shall consist
of the string s, a colon, a space, and a string
describing the signal number sig; otherwise
psignal
shall display only a message describing
the signal number sig. If
sig is invalid, the message displayed shall
indicate an unknown signal.
The array sys_siglist holds the signal description strings indexed by signal number.