pathalias -- Command

Generate a set of paths among computers
/usr/lib/mail/pathalias [-ivcDf] [-d link] [-l host] [-t link]  [  datafile
... ]

The command  pathalias computes the  shortest path and  corresponding route
from a  host to every  other known, reachable host.   It reads host-to-host
connectivity information from the standard input or datafile, then writes a
list of  host-route pairs onto the standard  output.  This command normally
is  used only  by  administrators of  busy  systems, to  maintain the  path
information used by smail.

pathalias recognizes the following command-line options:

-c   Print costs: print the path cost before each host-route pair.

-D   Terminal domains: see domains section, below.

-d arg
     arg is a dead link, host, or network.  If arg is of the form

         host-1!host-2

     pathalias treats the link from  host-1 to host-2 as an extremely high-
     cost  (i.e., dead)  link.  If  arg  is a  single host  name, pathalias
     treats that  host as dead  and uses it  on any path only  as the relay
     host of last  resort.  If arg names a network,  the network requires a
     gateway.

-f   First-hop cost: the  printed cost is the cost to  the first relay in a
     path, instead  of the  cost of the  entire path.  This  option implies
     (and overrides) option -c.

-i   Ignore case:  map all host names  to lower case.  By  default, case is
     significant.

-l host
     Set the  name of the local  host to host. By  default, pathalias reads
     file /etc/uucpname to discover the name of your system.

-t arg
     Output trace information for arg onto the standard error.

-v   Verbose: report some statistics on the standard error output.

Input Format

A  line  that  begins  with  white  space  continues  the  preceding  line.
pathalias ignores anything following a `#'.

A list of a host-to-host connection  consists of a from host in column one,
followed by  white space, followed  by a comma-separated list  of to hosts,
called links. A link may be  preceded or followed by a network character to
use in  the route.  Valid  network characters are `!'  (default), `@', `:',
and `%'.  A  link (and network character, if present)  can be followed by a
``cost'' enclosed between parentheses.

The cost  is an arithmetic  expression that includes  numbers, parentheses,
and  the  operators  `+',  `-',  `*',  and `/'.   It  cannot  be  negative.
pathalias recognizes the following symbolic costs:

LOCAL     A local-area-network connection.  Set cost to 25.

DEDICATED A high-speed dedicated link.  Set cost to 95.

DIRECT    A toll-free telephone call.  Set cost to 200.

DEMAND    A long-distance telephone call.  Set cost to 300.

HOURLY    An hourly poll.  Set cost to 500.

EVENING   A time-restricted telephone call.  Set cost to 1,800.

DAILY     A daily poll (also called POLLED).  Set cost to 5,000.

WEEKLY    An irregular poll.  Set cost to 30,000.

In addition,  the symbolic cost  DEAD is a very  large number (effectively,
infinite);  HIGH and  LOW are  -5  and +5,  respectively, for  baud-rate or
quality bonuses/penalties;  and FAST is  -80, for adjusting  costs of links
that use  high-speed modems  (9600 baud  or faster).  These  symbolic costs
represent an  imperfect measure of bandwidth,  monetary cost, and frequency
of connections.   For most  mail traffic, it  is important to  minimize the
number  of hosts  in a  route; for  this reason, HOURLY  times  24  is much
larger than  DAILY. If no cost  is given, pathalias uses  a default cost of
4,000.

For the  most part, an arithmetic expression  that mixes symbolic constants
other than  HIGH, LOW,  and FAST  makes no sense.   For example, if  a host
calls a local neighbor whenever there  is work, and in addition polls every
evening, the cost is DIRECT, not DIRECT+EVENING.

Examples

Consider the following input:

    down      princeton!(DEDICATED), tilt,
              %thrash(LOCAL)
    princeton topaz!(DEMAND+LOW)
    topaz     @rutgers(LOCAL+1)

If a link is encountered more than once, the least-cost occurrence dictates
the cost  and network character.   pathalias treats links  as bidirectional
but asymmetric:  for each link  declared in the input,  pathalias assumes a
DEAD reverse link.

If  the ``to''  host in  a link  is enclosed  by angle  brackets, pathalias
regards the link as being  terminal, and heavily penalizes all links beyond
it.  For example, when given the input

    seismo    <research>(10), research(100), ihnp4(10)
    research  allegra(10)
    ihnp4     allegra(50)

pathalias  generates  a direct  path  from site  seismo  to site  research;
however,  the path  from  seismo to  allegra  uses ihnp4  as  a relay,  not
research.

The set  of names by which  a host is known to its  neighbors is called its
aliases. Aliases are declared as follows:

    name = alias, alias ...

name  is the name  by which  the host  is known to  its predecessor  in the
route.

Fully connected networks, such as the Internet or a local-area network, are
declared as follows:

    net = {host, host, ...}

The list  of hosts may be  preceded or followed by  a routing character (by
default, `!'), and may be followed  by a cost (default 4,000).  The network
name  is optional;  if not  given,  pathalias makes  one up.   Consider the
following input:

    etherhosts = {rahway, milan, joliet}!(LOCAL)
    ringhosts = @{gimli, alida, almo}(DEDICATED)
    = {etherhosts, ringhosts}(0)

The  routing character  used in  a  route to  a network  member is  the one
encountered when  ``entering'' the network.  For  details, see the sections
on gateways and domains, below.

If you wish to give connection  data, but also wish to hide the host names,
use a declaration of the form:

    private {host, host, ...}

pathalias will not  generate a route to a private  host, but it may produce
routes through  it.  The  scope of a  private declaration extends  from the
declaration either to the end of  the input file in which it appears, or to
a private declaration with an  empty host list, whichever comes first.  The
latter scope  rule lets you retain the semantics  of a private declarations
when you pass data to pathalias via the standard input.

Dead hosts,  links, or  networks may  be presented in  the input  stream by
declaring

    dead {arg, ...}

where arg has the same form as the argument to the command-line option -d.

To force a specific cost for a link, use

    delete {host-1!host-2}

to delete all prior declarations,  then re-declare the link as desired.  To
delete a host and all its links, use the instruction:

    delete {host}

Diagnostic messages  name the file in which pathalias  found the error.  To
change the file's name, use the instruction:

    file {filename}

You can  fine-tune an entry  by adjusting the  weights of all  links from a
given host.  For example:

    adjust {host-1, host-2(LOW), host-3(-1)}

If no cost is given, pathalias uses a default of 4,000.

The  following  script  pipes into  pathalias  input  from compressed  (and
uncompressed) files:

    for i in $*; do
        case $i in
            *.Z)    echo "file {`expr $i : '.Z'`}
                zcat $i ;;
            *)  echo "file {$i}"
                cat $i ;;
        esac
        echo "private {}"
    done

Output Format

pathalias writes  to the standard output a list  of host-route pairs, where
the route is a string appropriate for use with printf(), e.g.:

    rutgers  princeton!topaz!%s@rutgers

%s in  the route string  is replaced by  the name of  the user to  whom the
message is being sent.  This task  normally is performed by a mailer, e.g.,
mail or elm.

Except for domains,  the name of a network is  never used in routes.  Thus,
in  the earlier  example, the  path  from down  to up  would be  up!%s, not
princeton-ethernet!up!%s.

Gateways

pathalias  represents a  network  by a  pseudo-host  and a  set of  network
members.  Links  from the members to  the network have the  weight given in
the input, whereas the cost from  the network to its members is zero.  If a
network  is declared  dead, the  member-to-network  links are  marked dead,
which effectively prohibits access to the network from its members.

If, however,  the input also  shows an explicit  link from any  host to the
network,  then that  host can  be used  as a  gateway.  In  particular, the
gateway need  not be a network  member.  For example, if  CSNET is declared
dead and the input contains

    CSNET = {...}
    csnet-relay CSNET

then routes to CSNET hosts will use csnet-relay as a gateway.

Domains

A  network whose  name begins  with  `.' is  called a  domain. Domains  are
assumed to require gateways, i.e., they are DEAD. The route given by a path
through a domain is similar to that for a network, but here the domain name
is tacked  onto the end of  the next host.  Subdomains  are permitted.  For
example, the definition

    harvard  .EDU   # harvard is gateway to .EDU domain
    .EDU   = {.BERKELEY, .UMICH}
    .BERKELEY = {ernie}

yields:

    ernie   ...!harvard!ernie.BERKELEY.EDU!%s

Output is  given for  the nearest  gateway to a  domain.  For  example, the
example above yields:

    .EDU   ...!harvard!%s

Output is given for a subdomain if it has a different route than its parent
domain, or if all its ancestor domains are private.

If the you  use its command-line option -D, pathalias  treats a link from a
domain to a host member of  that domain as terminal.  This property extends
to host  members of subdomains,  etc., and discourages routes  that use any
domain member as a relay.

Files

/usr/local/lib/palias.dir -- Default output
/usr/local/lib/palias.pag -- Default output
comp.mail.maps -- Likely location of some input files

See Also

commands,
mail [overview],
pathmerge,
smail
Honeyman P., Bellovin, S.M.: PATHALIAS, or the care and feeding of relative
addresses.  Atlanta, Proceedings of the Summer USENIX Conference, 1986.

Notes

This command is not used by the implementation of smail that COHERENT uses.
It is included, however, for compatibility with other implementations.

The order  of arguments is  significant.  In particular, options  -i and -t
should appear early.

© 2012 by Stephen A. Ness