Calling Other Systems
=====================

   By default `uucp' and `uux' will automatically start up `uucico' to
call another system whenever work is queued up.  However, the call may
fail, or you may have put in time restrictions which prevent the call
at that time (perhaps because telephone rates are high) (*note When to
Call::.).  Also, a remote system may have work queued up for your
system, but may not be calling you for some reason (perhaps you have
agreed that your system should always place the call).  To make sure
that work gets transferred between the systems withing a reasonable
time period, you should arrange to periodically invoke `uucico'.

   These periodic invocations are normally triggered by entries in the
`crontab' file.  The exact format of `crontab' files, and how new
entries are added, varies from system to system; check your local
documentation (try `man cron').

   To attempt to call all systems with outstanding work, use the command
`uucico -r1'.  To attempt to call a particular system, use the command
`uucico -s SYSTEM'.  To attempt to call a particular system, but only
if there is work for it, use the command `uucico -C -s SYSTEM'.  (
see Invoking uucico.).

   A common case is to want to try to call a system at a certain time,
with periodic retries if the call fails.  A simple way to do this is to
create an empty UUCP command file, known as a "poll file".  If a poll
file exists for a system, then `uucico -r1' will place a call to it.
If the call succeeds, the poll file will be deleted.

   A poll file can be easily created using the `uux' command, by
requesting the execution of an empty command.  To create a poll file for
SYSTEM, just do something like this:
     uux -r SYSTEM!
   The `-r' tells `uux' to not start up `uucico' immediately.  Of
course, if you do want `uucico' to start up right away, omit the `-r';
if the call fails, the poll file will be left around to cause a later
call.

   For example, I use the following crontab entries locally:

     45 * * * * /bin/echo /usr/lib/uucp/uucico -r1 | /bin/su uucpa
     40 4,10,15 * * * /usr/bin/uux -r uunet!

   Every hour, at 45 minutes past, this will check if there is any work
to be done, and, if there is, will call the appropriate system.  Also,
at 4:40am, 10:40am, and 3:40pm, this will create a poll file file for
`uunet', forcing the next run of `uucico' to call `uunet'.