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uucp_intro(7)
NAME
uucp_intro - UNIX-to-UNIX Copy Program (UUCP) introductory information
DESCRIPTION
The UNIX-to-UNIX Copy Program (UUCP) is a group of programs that support
communications between two computers running UNIX operating systems.
Tru64 UNIX supports the HoneyDanBer version of UUCP. The UUCP system
enables batched, error-free file transfer and remote command execution
between two UNIX systems. The UUCP system is most frequently used to
transfer electronic mail, network news, and public domain software over
low-speed, low-cost communications links.
A worldwide network that functions through the informal cooperation of the
user community has grown up around UUCP. The UUCP network is a series of
point-to-point links, with the majority of sites located in Europe and
North America.
The UUCP protocol itself supports only direct connections between two
systems. However, electronic news and mail delivery depend on third-party
forwarding. To facilitate mail and news delivery, most connected sites are
willing to relay files for other sites. The UUCP network depends on direct
distance dialing networks and off-peak long distance rates for its
continued functioning.
The UUCP Software
The UUCP software contains the following components:
· System directories that contain UUCP files and programs.
· Configuration files that contain information needed to establish
remote connections and determine access permissions.
These files are used to describe the UUCP operating environment to the
uucico daemon. Configuration files specify, for example, remote system
names, times of data transfer, valid login names, passwords, and the
commands that can be executed on a system.
· Administrative files that are used primarily in transferring data
between computers
Log files record both successful and failed data transfers by the
administrative files. Logs can occupy much disk space unless you
regularly delete some of them. The UUCP system provides facilities for
pruning log files.
Spool or queue files contain the data and transfer requests that are
issued from the uucp and uucico commands. There are several types of
spool files:
-- Execution files are generated only by the uux command. They
contain the commands to be executed on the remote system. By
convention, execution files are named X.filename.
-- Command files are created by both the uucp and uux commands. They
contain commands for transferring files to remote systems. By
convention, command files are named C.filename.
-- Data files contain the data that is transferred to remote
systems. They are created by the uucp and uux commands. By
convention, data files are named D.filename.
· Public directories that contain the files transferred by UUCP.
· User commands that perform the basic UUCP functions, such as file
transfer and remote command execution.
The uucp and uux commands allow remote file copy and command
execution, respectively. Both commands allow users to specify remote
system names in pathnames.
The uucp and cp commands use similar syntax. However, cp works
immediately and copies files on the local system, while uucp operates
in batch mode and allows file transfers between two systems. User
requests are queued to public spool files where they wait for further
processing by the uucico daemon (UNIX-to-UNIX copy-in, copy-out
program).
The uux command provides a shell-like environment for issuing commands
on remote systems. As the user works, the uux command generates an
execute file that is sent to a spool directory to await transfer to a
remote system.
· Administrative commands, such as programs that enable you to configure
and maintain UUCP.
· Daemon programs that handle file transfers, communications with
TCP/IP, scheduling of work, and remote command executions.
The uucico daemon, together with its subprocesses, manages machine-
to-machine communications. It works through control and log files, as
well as a set of public directories that contain the requests
generated by the uucp and uux commands.
The UUCP system can use any of several physical and transport layer
protocols. The uucico daemon supports both direct and remote connections
through a serial interface. Typically, remote connections use modems and
direct distance dialing networks. The UUCP system uses error-correcting
modem protocols to ensure data integrity during transfer.
The uucpd daemon supports UUCP over TCP/IP networks. It performs login and
password authentication before it starts the uucico daemon. This
configuration option allows you to take advantage of high-speed local area
networks in order to do batched file transfers. Note that TCP/IP does not
replace UUCP protocols; it serves as a transport mechanism only.
Because users on remote systems can log in, transfer files, and execute
commands, UUCP is a potential security problem for the local system. The
UUCP system does provide a means to restrict what users can do on the local
system, and likewise local UUCP users can be similarly restricted by remote
systems.
Although many installations use UUCP to support electronic mail and news
only, UUCP is not restricted to these uses. For systems without LAN
connections, UUCP can provide data transfer capabilities not otherwise
available.
The UUCP File and Directory Structure
The UUCP system uses several directories and files to track its activities.
These directories and files include:
· Public directories with unrestricted access rights
· Administrative directories and subfiles
· Configuration files
· Lock files
Most UUCP directories and files are included when the software is
installed. Some administrative files are created by various UUCP programs
as they run.
The UUCP public directory (/var/spool/uucppublic) contains files
transferred to the local system from other systems. The files remain in the
public directory until users claim them or until the commands requested by
users on remote systems are executed by the uuxqt daemon. If the files were
sent to the UUCP public directory with the uuto command, the user must
claim them with the uupick command. Otherwise they can copy the files from
that directory manually. The uucppublic directory, which contains a
subdirectory for each remote system that sends files to the local system,
is created when UUCP is installed.
The UUCP configuration files reside in the /usr/lib/uucp directory. You
configure these files for systems at your site. You must configure the
following files:
· Systems
· Devices
· Permissions
Configuring the other files is optional.
The configuration files contain information about remote systems contacted
by UUCP, the devices used to contact these systems, the times to contact
the systems, and the level of access that remote systems can have to the
local system. Some configuration files also specify limits on UUCP
activities to prevent the local system from becoming overloaded.
For details about UUCP configuration files, refer to the Network
Administration: Services manual.
Whenever UUCP connects to a remote computer, it makes a lock file for both
the local and remote communication devices in the /var/spool/locks
directory. Lock files on remote devices prevent other instances of the
uucico daemon from establishing duplicate connections to the same remote
system. When a local device contains a lock file, UUCP waits until the
device becomes available, or it uses another device for communications.
The UUCP Daemons
Normally, on an OSF/1 system, UUCP components reside in the /usr/adm,
/usr/lbin, and /etc/uucp directories. However, on the Tru64 UNIX system,
the UUCP daemons are stored in the /usr/lib/uucp directory, except for the
uucpd daemon, which is stored in the /usr/sbin directory. The following
table lists the daemons and their functions.
_________________________________________________
Name Function
_________________________________________________
uucico Manages file transfers
uusched Manages job scheduling
uuxqt Performs remote command execution
uucpd Enables UUCP connections through TCP/IP
_________________________________________________
In a typical configuration, the cron daemon automatically starts the
uucico, uusched, and uuxqt commands according to a schedule set by the
system administrator. For testing and debugging the UUCP configuration, the
daemons also can be started by someone with superuser privileges.
See cron(8) for more information.
The uucico Daemon
The uucico daemon transports the files required to send data from one UNIX
system to another UNIX system. Most UUCP directories are created when UUCP
is installed; however, the uucico daemon also creates some files during its
operation. The uucico daemon performs the following tasks:
· Scans spool directories for jobs
· Contacts remote systems at times you specify
· Selects data transfer protocols
· Exchanges jobs with remote systems
· Logs jobs requested and completed
When the uucico daemon initiates contact with remote systems, it operates
in master mode. In this mode, the uucico daemon starts another slave
process on the remote system. When it operates in master mode, the uucico
daemon attempts to process jobs queued on its local system; in slave mode
the uucico daemon carries out requests made by a remote uucico process.
Once the uucico daemon is finished processing its locally queued jobs on
the remote system, the two processes can switch their roles as master and
slave in order to exchange data in both directions.
The uucp and uux commands each start the uucico daemon to transfer command,
data, and execute files to the designated system. The uucico daemon is also
started periodically by the uusched daemon, which handles the transfer of
files queued in the local spooling directory.
Once started by the uusched daemon, the uucico daemon attempts to contact
other systems and execute the instructions in the command files. To
execute those instructions, the uucico daemon checks the
/usr/lib/uucp/Systems file to find an entry for the system to be called.
Then, it checks the Systems file entry to see if the current time is a
valid time to call. If so, it checks the Type and Class fields in the
Systems file, and searches the /usr/lib/uucp/Devices file to find a device
that matches these fields.
After it finds a device, the uucico daemon checks the /var/spool/locks
directory to ensure that the device is not locked by another process. If
the device is locked, the daemon checks for another device of the requested
type and speed, and uses it, if available.
When no device is available, the daemon returns to the Systems file to find
another entry for the remote system. If one exists, the daemon repeats the
process of searching for a device. If none is found, the daemon records the
attempt to contact the remote system in the file
/var/spool/uucp/.Status/SystemName and goes on to process the next request.
The command file remains in the queue, and the uucico daemon repeats the
transfer attempt.
When the uucico daemon reaches the remote system, it logs in using the
information in the local Systems file pertaining to the remote system file.
Logging in causes an instance of the uucico daemon to be invoked on the
remote system.
The two daemons, one on each system, work together to make the transfer.
The uucico daemon on the calling system controls the link, specifying the
requests to be performed. The uucico daemon on the remote system checks
the local permissions to see whether they allow the request to be
performed. If so, the file transfer starts.
After the uucico daemon on the calling system finishes transferring all the
requests it has for the remote system, it sends a hang-up request. When the
remote uucico daemon has transactions to send to the calling system, it
denies the hang-up request, and the two daemons reverse roles.
The /usr/lib/uucp/Permissions file on either the local or the remote system
can forbid the daemons to reverse roles. In such cases, the remote system
must wait to transfer files until it calls the local system. When nothing
is left to be transferred in either direction, the two daemons hang up.
Throughout the transfer process, the uucico daemons on both systems write
messages in UUCP log and error files.
The uusched Daemon
The uusched daemon schedules the transfer of files that are queued in the
local spooling directory /var/spool/uucp. When the uusched daemon is
invoked, it scans the spooling directory for command files, then randomizes
the files and starts the uucico daemon, which actually transfers the files.
The uuxqt Daemon
The uuxqt daemon interprets execution files created on a remote system and
transferred to the local system by the uucico daemon. Normally, the uucico
daemon starts the uuxqt process to execute queued X* files. The uuxqt
daemon searches the spool directory for command execution requests. When it
locates such a request, the uuxqt daemon checks for necessary files and
permissions and then, if permitted, executes the specified command.
The uucpd Daemon
The uucpd daemon handles communications between UUCP and TCP/IP. This
daemon enables users on systems linked over a local area network to
establish UUCP connections to other systems. Its job is to perform login
authentication before transferring control to the uucico daemon, which
completes the data transfer. The uucpd daemon is started by the inetd
daemon, after configuring the /etc/inetd.conf and /etc/services files, and
is not required to be running on the local side.
For details, refer to the Network Administration: Services manual.
SEE ALSO
Commands: ct(1) ,cu , tip(1) ,uucico , uucleanup(8), uuencode(1), uulog(1),
uuname(1), uupick(1), uusched(8), uusend(1), uustat(1), uuto(1), uux(1),
uuxqt(1)
Network Administration: Services
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Index for
Section 7 |
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Alphabetical
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Top of
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