qmail-popup.8

linux下qmail的源码 本人加了一些注释

.TH qmail-popup 8
.SH NAME
qmail-popup \- read a POP username and password
.SH SYNOPSIS
.B qmail-popup
.I hostname
.I subprogram
.SH DESCRIPTION
.B qmail-popup
reads a POP username and password from the network.
It then runs
.IR subprogram .

.B qmail-popup
is most commonly invoked from
.B inetd
as

.EX
   qmail-popup CHANGEME checkpassword qmail-pop3d Maildir
.EE

with
CHANGEME
replaced by the fully qualified domain name of the local host.

.B qmail-popup
expects descriptor 0 to read from the network
and descriptor 1 to write to the network.
It reads a username and password from descriptor 0
in POP's USER-PASS style or APOP style.
It invokes
.IR subprogram ,
with the same descriptors 0 and 1;
descriptor 2 writing to the network;
and descriptor 3 reading the username, a 0 byte, the password,
another 0 byte, 
an APOP timestamp derived from
.IR hostname ,
and a final 0 byte.
.B qmail-popup
then waits for
.I subprogram
to finish.
It prints an error message if
.I subprogram
crashes or exits nonzero.

.B qmail-popup
should be used only within
a secure network.
Otherwise an eavesdropper can steal passwords.
Even if you use APOP,
an active attacker can still take over the connection
and wreak havoc.

.B qmail-popup
has a 20-minute idle timeout.

.B qmail-popup
is based on a program contributed by Russ Nelson.
.SH "SEE ALSO"
maildir(5),
qmail-local(8),
qmail-pop3d(8)