VMS/IRAF Installation and Site Manager's Guide

5.6. [IRAF.DEV]HOSTS, UHOSTS, and IRAFHOSTS

The dev directory contains several files (hosts, irafhosts, and uhosts) used by the IRAF network interface. IRAF networking is used to access remote image displays, printers, magtape devices, files, images, etc., via the network. IRAF network nodes do not have to have the same architecture, or even run the same operating system, i.e., one can access a UNIX/IRAF node from VMS/IRAF and vice versa. V2.10 IRAF contains extensive changes to the networking code to permit remote client access to a VMS node via TCP/IP, and runtime selection of either TCP/IP or DECNET for the transport method. Editing changes to the networking related files in [IRAF.DEV] are illustrated here. Further documentation on the networking interface can be found in the IRAF Version 2.10 Revisions Notes and §7.1 of this manual.

The dev$hosts file is used to configure IRAF networking on the local system. This file tells IRAF what network nodes are defined and how to connect to them, including the protocol to be used. Initially IRAF networking is disabled. To enable networking there must be an entry in the hosts file for the host IRAF is running on. To do anything useful with networking there must also be entries for the nodes you wish to connect to. Often a single VMS/IRAF installation and a single copy of dev$hosts are shared by several nodes in a VMS cluster.

To connect to a local VMS node via DECNET requires an entry in the hosts file like the following (these and the following examples are taken from the NOAO VMS/IRAF hosts file).

robur r                 : robur::0=irafks
draco                   : draco::0=irafks

Here, nodes "robur" and "draco" are defined as DECNET-connected nodes with the IRAF kernel server (IRAFKS) installed as a "zero numbered" object in DECNET. IRAFKS can also be installed as a numbered DECNET service, in which case the hosts file entry should appears as follows.

robur r                 : robur::242
draco                   : draco::242

In this example the IRAFKS service is installed locally as object number 242 in DECNET.
To connect to a node on a remote UNIX host via TCP/IP requires an entry using "!" to indicate the TCP/IP protocol, followed by the UNIX command to be executed to start up the IRAF kernel server, as in the following examples (note the different machine types).

cephus                  : cephus!/usr/iraf/bin.ddec/irafks.e
columba                 : columba!/usr1/iraf/iraf/bin.mips/irafks.e
felis                   : felis!/u1/iraf/iraf/bin.rs6000/irafks.e
lepus                   : lepus!/usr/iraf/bin.f2c/irafks.e
noctua                  : noctua!/usr/iraf/iraf/bin.irix/irafks.e
ursa u                  : ursa!/local/iraf/bin.sparc/irafks.e
vega                    : vega!/iraf/iraf/bin.hp700/irafks.e

Finally, the hosts file may contain logical node entries. These are not real network nodes, but hosts file entries which point to some other entry in the same host table. These are most commonly used to designate logical nodes for disposing of output to different classes of devices such as printers and plotters, hosted by some node elsewhere on the network, but can be used for other purposes such as gateways.

# Logical nodes (lpnode = line printer output, plnode = plotter output).
lpnode                  : @ursa
plnode                  : @ursa

In the example above node ursa is a Sun server; the hosts file entry for this node is given in an earlier example above.

The other files required to configure IRAF networking are the uhosts and irafhosts files. The uhosts file is a standard internet host table containing hostnames and internet numbers. It is used for TCP/IP networking unless the logical name IRAFUHNT is defined to point to an alternate file (e.g., Multinet uses a hosts file which IRAF networking can access directly). The uhosts file, if used, should be replaced by a host listing for your local site. One way to do this is to copy the /etc/hosts file from a local UNIX host. Note that V2.10 VMS/IRAF TCP/IP networking does not support runtime lookup of hostnames via a name service, hence an internet host must have an entry in the uhosts or IRAFUHNT file for VMS/IRAF to be able to connect to the host.

The irafhosts file supplies login information used by IRAF networking when a connection is made. When a network login is attempted the networking system will use the user's .irafhosts file if there is one, otherwise it defaults to the irafhosts file in dev. The system version of irafhosts should not need to be modified unless proxy logins are enabled on the local host. Proxy logins are used to eliminate password prompts when making network connections between cooperating machines in the local VMS cluster. This is a desirable but optional feature in all but one case, network gateways. When IRAF network connections are routed through a local VMS machine serving as a gateway machine password prompts are not possible, and one must either enable proxy logins or supply each user with a .irafhosts file containing their password. Proxy logins are probably the least objectionable of these two options.

Thus far we have discussed the IRAF networking configuration only as it appears from the VMS side of the network, i.e., what one sees when configuring the dev$hosts and other files on a VMS host. This is sufficient to allow one VMS/IRAF host to network to another, or to allow a VMS/IRAF host to connect to an external host machine running UNIX. The remaining case occurs when IRAF running on a UNIX host connects to VMS/IRAF. To enable such "incoming" TCP/IP network connections one must make an entry for each VMS host in the dev$hosts file on the UNIX/IRAF (client side) host, as in the following example.

# VMS (decnet) nodes, via internet gateway robur.
robur r                 : -rcb robur!irafks
draco                   : @robur!draco
grian                   : @robur!grian
lenore                  : @robur!lenore
vela                    : @robur!vela

In this example all incoming (TCP/IP) connections are routed via the VMS gateway machine robur. The "irafks" is a DCL symbol defined on the server node in hlib$irafuser.com which runs the IRAF kernel server, irafbin:irafks.exe. The "@robur!nodename" syntax for the VMS nodes other than robur tells IRAF running on the UNIX host to use node robur as the gateway. The connection to node robur is made via the rexec-callback IRAF networking connect protocol (see §7.1 and also the V2.10 IRAF system notes file). The connection from the gateway machine to the target VMS node is controlled by the dev$hosts file on the gateway (VMS) node, and will often be a DECNET connection, hence the gateway can serve to connect the TCP/IP and DECNET domains.

Once again, for gateway connects to succeed either proxy logins must be enabled on the gateway machine, or each user must have a .irafhosts file on the gateway machine containing password information. For incoming TCP/IP network connections to work the VMS node must support the rexec network service, which is only available via third party networking packages such as Multinet. However, since IRAF networking supports gateways only the gateway host need run this software. When properly configured, gateways are transparent to the user.

To fully configure IRAF networking some VMS-level configuration is necessary in addition to editing the hosts, uhosts, and irafhosts files (for example IRAFKS should be defined as a known DECNET service). This is discussed further in §7.1.