Rewrote various parts.

man2/signal.2

@@ -1,4 +1,5 @@
 .\" Copyright (c) 2000 Andries Brouwer <aeb@cwi.nl>
+.\" and Copyrigh (c) 2007 Michael Kerrisk <mtk-manpages@gmx.net>
 .\" based on work by Rik Faith <faith@cs.unc.edu>
 .\" and Mike Battersby <mike@starbug.apana.org.au>.
 .\"
@@ -24,7 +25,8 @@
 .\"
 .\" Modified 2004-11-19, mtk:
 .\" added pointer to sigaction.2 for details of ignoring SIGCHLD
-.\" 2007-06-03, mtk: strengthened portability warning.
+.\" 2007-06-03, mtk: strengthened portability warning, and rerote
+.\"     various sections.
 .\"
 .TH SIGNAL 2 2007-06-03 "Linux" "Linux Programmer's Manual"
 .SH NAME
@@ -45,39 +47,43 @@ and has also varied historically across different versions of Linux.
 instead.
 See \fIPortability\fP below.
 
-The
 .BR signal ()
-system call installs a new signal handler for the signal with number
-.IR signum .
-The signal handler is set to
-.I handler
-which may be a user specified function, or either
-.B SIG_IGN
-or
-.BR SIG_DFL .
+sets the disposition of the signal
+.IR signum
+to
+.IR handler ,
+which is either
+.BR SIG_IGN ,
+.BR SIG_DFL ,
+or the address of a programmer-defined function (a "signal handler"),
 
-Upon arrival of a signal with number
+If the signal
 .I signum
-the following happens.
-If the corresponding handler is set to
+is delivered to the process, then one of the following happens:
+.TP 3
+*
+If the disposition is set to
 .BR SIG_IGN ,
 then the signal is ignored.
-If the handler is set to
+.TP
+*
+If the disposition is set to
 .BR SIG_DFL ,
 then the default action associated with the signal (see
 .BR signal (7))
 occurs.
-Finally, if the handler is set to a function
-.I handler
-then first either the handler is reset to SIG_DFL
-or an implementation-dependent blocking of the signal
-is performed, and then
+.TP
+*
+If the disposition is set to a function,
+then first either the disposition is reset to
+.BR SIG_DFL ,
+or the signal is blocked (see \fIPortability\fP below), and then
 .I handler
 is called with argument
 .IR signum .
-
-Using a signal handler function for a signal
-is called "catching the signal".
+If invokation of the handler caused the signal to be blocked,
+then the signal is unblocked upon return from the handler.
+.PP
 The signals
 .B SIGKILL
 and
@@ -88,10 +94,17 @@ cannot be caught or ignored.
 returns the previous value of the signal handler, or
 .B SIG_ERR
 on error.
+.SH ERRORS
+.TP
+.B EINVAL
+.I signum
+is invalid.
 .SH "CONFORMING TO"
 C89, C99, POSIX.1-2001.
 .SH NOTES
-The effects of this call in a multi-threaded process are unspecified.
+The effects of 
+.BR signal ()
+in a multi-threaded process are unspecified.
 .PP
 According to POSIX, the behaviour of a process is undefined after it
 ignores a