sendmail, 4th Edition

-d52.1

Show disconnect from controlling TTY Debug command-line switch

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 on page 1040) 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).