paths -- System Administration

Routing data base for mail
/usr/lib/mail/paths

File /usr/lib/mail/paths holds the data base that the command smail uses to
route mail.

Each  line gives  routing  information to  a  host, and  has the  following
format:

    host    route   [cost]

host names a remote host.  The  route field details the route by which mail
can travel  from your system to  host. Note that it  includes the printf()-
style  format string  ``%s''.   This field  uses the  bang-path format  for
describing a route.  For example, if you access site foo via site bar, then
route field for site bar reads:

    bar foo!bar!%s

smail uses the optional field cost  to decide whether to queue mail that is
spooled for other  systems, or to invoke the command  uucico to deliver the
mail  immediately.   If  the   cost  is  at  or  below  smail's  ``queueing
threshold'', then  smail attempts to  deliver it immediately.   This speeds
mail delivery between hosts that enjoy  an inexpensive UUCP link, such as a
serial line; and batches mail that  must be sent over expensive media, such
as long-distance telephone.  If the  cost field is absent, smail gives this
host a cost value above that of its queueing threshold.

Note that  the value in  the costs field  does not override  the connection
times set in the UUCP file sys. Thus, this field is useful only for systems
that you can call any time, or that you call frequently.

Example

The  following  gives a  sample  paths  file for  a  COHERENT system  named
lepanto:

     friend       friend!%s   300
     hubsys       hubsys!%s   95
     lepanto      %s          0
     lepanto.ampr.org         %s0
     widget       hubsys!widget!%s95

As this  file shows, lepanto  is linked to  systems hubsys and  friend. The
cost of 95 associated with hubsys  is low, and is appropriate to a low-cost
link,  such as  a hard-wired  link.   On the  other hand,  the cost  of 300
associated with  friend is high,  which indicates that  the connection with
friend is expensive, such as a long-distance telephone connection.  If cost
is 100  or greater, mail will  be queued for later  delivery.  A cost below
100 tells smail to attempt immediate delivery.

In  this example,  machine lepanto  is registered  in the  domain ampr.org.
``ampr'' is  an abbreviation for ``Amateur  Packet Radio,'' which indicates
that  lepanto  is a  packet-radio  node.  Note  that  machine name  lepanto
appears   in  both   conventional  form   (``lepanto'')  and   domain  form
(``lepanto.ampr.org''); this is done to make it easier for smail to resolve
addresses.

lepanto can use hubsys to forward mail to widget. Thus, when smail receives
mail for system widget, it will transmit it to hubsys for forwarding.  Note
that hubsys's administrator must have given lepanto permission to use it as
a mail relay, or this will not work.

See Also

Administering COHERENT,
mail [overview],
smail

Notes

Please  note that  the mail-routing  program smail  does not  actually read
/usr/lib/mail/paths when  it processes mail;  rather, it reads  a DBM-style
data base that is built from this file.  The DBM data base can be read much
faster  than an  ordinary text  file, thus improving  the speed  with which
smail handles mail.  Thus, when you edit paths, you must invoke the command
mkpaths to ``cook'' its contents into  DBM format, so smail see the changes
you have  made.  For information  on DBM-style data bases,  see the Lexicon
entry for libgdbm.

© 2012 by Stephen A. Ness