-bd
Run as a daemon All versions
The -bd
command-line switch causes
sendmail to become a daemon,
running in the background, listening for and
handling incoming SMTP connections.[107]
To become a daemon, sendmail
first performs a fork(2). The
parent then exits, and the child becomes the daemon
by disconnecting itself from its controlling
terminal. The -bD
command-line switch can be used to prevent the
fork(2) and the detachment
and allows the sendmail
program’s behavior to be observed while it runs in
daemon mode.
As a daemon, sendmail does a listen(2) on TCP port 25 by default for incoming SMTP messages.[108] When another site connects to the listening daemon, the daemon performs a fork(2), and the child handles receipt of the incoming mail message.
[107] * In its classic
invocation, -bd
is usually combined with a -q1h.
[108] † Beginning with
V8.10, sendmail also listens
on port 587 for message submissions via MUAs. This
default behavior can be turned off with the
FEATURE(no_default_msa) (FEATURE(no_default_msa)
on page 635).
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