Starting with V8.10, the sendmail daemon can
accept a few control and status commands via a Unix-based named
socket. This interface is primarily intended for use with the tools
provided with the commercial version of
sendmail, but it can be equally valuable for use
with your own home-grown tools. The
ControlSocketName option enables this type of
controlling interface. It is declared like this:
O ControlSocketName=path configuration file (V8.10 and later)
-OControlSocketName=path command line (V8.10 and later)
define(`confCONTROL_SOCKET_NAME', path) mc configuration (V8.10 and later)
Here, the argument path, of type
string, is the full pathname of the Unix named
socket. The file named by path need not
exist. If it exists, sendmail will remove it and
create a new named socket. As a consequence, you should avoid
accidently declaring path with an existing
file. The file will be silently removed when
The path needs to be secure. That is,
every component of it should be owned by, and writable only by,
root or the trusted user specified in the
TrustedUser option (TrustedUser).
Because this interface can be used to shut down the
sendmail daemon, the socket requires extra
protection. On some operating systems (such as with Solaris and
pre-4.4 BSD kernels) it is not enough to make the socket mode 0600.
You should also place it in a directory that is
root owned and of mode 0700. On such operating
systems, if you put it in a directory that is world-searchable,
anyone on the same machine will be able to shut
down the daemon.
If the path specification is one where some component does not exist,
sendmail will log the following message and not
use a controlling socket:
daemon could not open control socket /vqr/spool/mqueue/.control: No such file or directory
Here, /vqr was mistyped, when
/var is what was meant.
An example of code that shows one way to use the controlling socket
is in contrib/smcontrol.pl, a
perl(1) script that requires version 5 or higher
perl to use. It gathers the name of the control
socket from the hardcoded filename
/etc/mail/sendmail.cf. To run it, you just
invoke it with a single argument:
# cd contrib
# ./smcontrol.pl help
Help for smcontrol:
help This message.
restart Restart sendmail.
shutdown Shut down sendmail.
status Show sendmail status.
memdump Dump allocated memory list (for debugging only).
End of HELP info
The contrib/smcontrol.pl program is a simple
command-line interface to the controlling socket. It should be
considered a prototype for developing your own, more sophisticated,
tools. Consider, for example, the usefulness of the
# ./smcontrol.pl status
Daemon Status: (process 13480) Accepting connections
Child Process 13560 Status: SMTP server child for 18.104.22.168
Child Process 13579 Status: SMTP server child for 22.214.171.124
Child Process 13584 Status: console socket child
This shows that the daemon is up, and that two
sites are connected to yours for the transmission of mail.
The ControlSocketName option is not safe. If
specified from the command line, it can cause
sendmail to relinquish its special privileges.