LINKING UP WITH THE OUTSIDE WORLD
An introduction to UUCP
by Bob Toxen
Officially, UUCP is short for UNIX
to UNIX copy program.
But in addition to a program for copying files between UNIX computers,
UUCP offers users a means of executing programs
remotely and sending network mail. Because of this, I prefer to think of
UUCP as meaning
to UNIX communications
The program to copy files is called UUCP and works
similarly to the cp utility. It takes two (or more)
arguments and copies the first file (and any subsequent files) to the last
filename (which may be a directory). Each argument, except the last, should
be the name of a file and may be preceded by a system name. The system name
should be separated from the filename by an exclamation mark (!), pronounced
by UNIX buffs as "bang."
For instance, to copy the file flight from your local system to one
called xorn, give the command:
% uucp -m -njill flight xorn\!~jill/flight
$ uucp -m -njill flight xorn!~jill/flight
The first command line would be used with the C shell while the second would
be used with the Bourne shell. As you might have guessed, I threw in a few
tricks. First, the -m flag tells uucp
to send you mail when the copy finishes. This is important because
uucp merely queues up a request to do the copy.
The copy operation itself may not occur for several hours depending on how
uucp is configured (on both systems) and what phase the
moon is in.
The second trick I used, -njill will cause
uucp to send mail to the account called jill on the
other system (named xorn) when the operation is done.
Third, since I do not know Jill's home directory path, I specified
~jill. This will be converted to her home directory's full
pathname on xorn by uucp and so will work with both
the C shell and the Bourne shell. C shell users must precede the
! separating the system name from the account name with a
backslash (\) since C shell normally treats exclamation marks as special
SECURITY AND PERMISSIONS
A common problem with using the uucp command appears in the
area of permissions. Not only must users tussle with the usual assortment of
UNIX file system permissions -- they must also thread their way through an
additional group of requirements. The source file flight in our
example must be readable by everyone. Also, the directory it is in (our
current directory in this case) and all directories leading to it must be
readable and executable by everyone. The destination file -- if it exists --
must also be writable by everyone. If a destination file does not exist,
the directory in which you intend to create a new file must be writable by
everyone. In any case, all directories leading to the file you create or
modify must be readable and executable -- just as the source directories must
Most people do not want their login directories writable by everyone because
if they were, anyone could remove files, either by accident or on purpose.
I solve this problem by creating a subdirectory under my login directory
called uucp, which I make writable by all. Also, I make sure
that any confidential files are not readable by others so as to prevent
someone on another system from using the uucp command to copy
confidential material to their system.
Because many users are not computer security experts and do not want to worry
about file permissions, many system administrators configure
uucp to allow only file transfers to and from pathnames
beginning with /usr/spool. The directory
/usr/spool/uucppublic, which is readable, writable
and executable by all, is provided for users to send and receive files.
Thus to send the file flight, one would give the commands:
% chmod 755 flight
% cp flight /usr/spool/uucppublic
% uucp -m -njill ~uucp/flight xorn\!~uucp
In this case, we assume the C shell is used. There should be an account called
uucp on each system with a login directory of
/usr/spool/uucppublic so that the C shell will know how to
expand ~uucp on the local system. Any occurrences not
expanded by the shell will be expanded by uucp. Jill would
% mv ~uucp/flight .
To move the file inter her login directory.
REMOTE PROGRAM EXECUTION
The program called uux is used for remote program
execution. You can invoke one program or you can invoke several by having
the output of one program piped to the input of the next. Standard input
and standard output may be redirected to and from files on other systems.
For example, if you are on the system called sauron and you want to
know who is logged into the system called xorn, you could issue the
% uux "xorn\!who > sauron\!~uucp/who.xorn"
The program uux will cause the who command
to be invoked on xorn and will accumulate the output in a temporary
file before using uucp to transfer that file back to the file
/usr/spool/uucppublic/who.xorn on sauron.
Alternatively, you could mail the results back, like so:
% uux "xorn\!who | mail (sauron\!bob)"
Note the parentheses around sauron\!bob to tell
uux not to interpret it as an input file. Otherwise,
uucp would see sauron\!bob as an argument to
rmail. It would be instructive to issue the commands listed
in Figure 1 and examine the results (even if your system is not configured
to allow them).
We can do more sophisticated operations -- such as printing files from many
systems -- like so:
% uux "xorn\!lpr sauron\!~bob/foo \
Most administrators only allow certain commands to be executed via
uux for security reasons.
Sending remote mail is very easy. To send mail to a remote system, simply
give the system name and the account name separated by an exclamation mark.
Thus, to send mail to jim on system its, give the command:
% mail its\!jim
What did you think of that talk? Pretty good, huh?
I'll be waiting to hear from you.
Unlike the other commands, mail can send data through
intermediate systems. Thus, I could give the command:
% mail olympus\!ucbvax\!dual\!fair
When will the next release of the
net-news software package be ready?
Will you be at UniOps?
This will send the message to olympus which will forward it to
ucbvax, which in turn will forward it to dual, where it
finally will be placed in the fair account.
Under System V, the restrictions against using uucp to
transfer files to and from systems other than those that talk directly to
yours have been lifted. The file must originate in
/usr/spool/uucppublic and be sent to the same directory on
the destination system. These indirect transfers may be controlled with the
ORIGFILE and FWDFILE files in
/usr/lib/uucp so as to keep bad guys from getting into your
To send mail to someone, all you need to know is the path to that person's
system. Most people know the path from their system to one of the major mail
exchanges, called backbone sites. The paths between these
installations are well known so you should be able to derive a path to the
system you are trying to send mail to if you can simply learn the path from
it to one of the backbone sites.
For example, my path from ucbvax is:
ucbvax!Shasta!olympus!bob. If I want to send mail to
someone whose path from ihnp4 is
ihnp4!mitse!bonzo!ronnie, I would give the command:
% mail Shasta\!ucbvax\!ihnp4\!mitse\!bonzo\!ronnie
<text of message>
The UUCP network is connected to various other networks. For example,
olympus is the gateway to the Silicon Graphics Ethernet, which has
dozens of workstations, smart graphics terminals and VAXen communication via
IP/TCP and XNS at 10 Mbaud. The UUCP network is also tied into the ARPANET
at numerous sites.
Addresses are specified differently on ARPANET. On each ARPANET system, the
paths to every other site are stor (there are far fewer ARPANET outposts
than UUCP sites, which numbered at least 3000 at last count). ARPANET users
also use an at-sign (@) instead of a bang character (!) and put
the user name to the left of the system name.
Thus, an account called berch on a system called LLL-TIS
would be referenced as berch@LLL-TIS.
% echo hello > ~uucp/foo
% uux "xorn\!echo sauron\!~uucp/foo >sauron\!~uucp/1"
% uux "xorn\!echo (sauron\!~uucp/foo) >sauron\!~uucp/2"
% uux "xorn\!ls -l sauron\!~uucp/foo >sauron\!~uucp/3"
% uux "xorn\!ls -l (sauron\!~uucp/foo) >sauron\!~uucp/4"
% /usr/lib/uucp/uucico -r1 -sxorn
Figure 1 -- Illustrative UUCP commands you may
wish to try yourself.
If I wanted to send mail to berch, I would have to send the letter to
a gateway system that understands the ARPANET syntax. One path might
% mail Shasta\!berch@LLL-TIS
Here, we use Shasta as the gateway. Since our system,
olympus, does not understand the ARPANET syntax, it just sends the
whole mess to Shasta for sorting when it sees the !
after that site name.
Note that a site does not actually have to be on the ARPANET to know how to
deal with it. We could even teach olympus to recognize at-signs and
know that it talks to a station on the ARPANET (Shasta). We could then give
% mail berch@LLL-TIS
and the olympus mailer could convert it to:
% mail Shasta\!berch@LLL-TIS
But olympus runs 4.2 BSD and does have the software to do this.
A domain name is sometimes appended to the address. A domain,
essentially, is the name of a network containing a number of systems. In
mail's "From" line, it is preceded by a period (.) and is
usually listed in capital letters. Thus a letter might be from:
If you wanted to send mail to this person from your system you would throw
away the .ARPA, knowing that su-Shasta is the
ARPANET name for a gateway to the UUCP network whose UUCP name is
Shasta. Thus it translates to:
Note that the first form (without .ARPA would be used to
send mail from an ARPANET site.
Bob Toxen is a member of the technical staff at Silicon Graphics, Inc.
He has gained a reputation as a leading uucp expert and is
responsible for ports of System V for the Zilog 8000 and System III for the
Copyright © 1984, 2007, 2014, 2020 Robert M. Toxen. All rights reserved.