When sendmail runs as a daemon, it must
disconnect itself from the terminal device that is used to run it.
This prevents keyboard signals from killing it and prevents it from
hanging (on a dial-in line waiting for carrier detect, for example).
The -d52.1 (a.k.a. -d52)
debugging switch shows sendmail disconnecting
from the controlling terminal device:
disconnect: In fd Out fd, e=addr
For both its input and output connections, the
fd is a decimal representation of the file
descriptor number. The addr is a hexadecimal
representation of the address that contains the envelope information.
If the LogLevel option (LogLevel) is greater than 71,
sendmail syslog(3)s the
following message to show that it has disconnected:
in background, pid=pid
Here, pid is the process identification number
of the child process (the daemon).