12.4 Remote use of AIPS

AIPS users do not always find themselves seated in front of the main display screen of the computer which they intend to use for their data analysis. AIPS provides facilities for such users which depend to some extent on the nature and location of the workstation or terminal at which the user is seated. Nearly seamless function is provided to a user seated at a workstation on the local Ethernet well known to the AIPS installation. Substantial capabilities are still available to the user at a more distant workstation capable of X-Windows display, especially if that workstation can also run AIPS programs such as the TV server and remote tape server. Even the user at a simple terminal or workstation, capable of emulating a Tektronix 4010, can still get some interactive displays. It is only the users at very simple (and now antique) terminals who will be rather limited in their interactive use of AIPS.

12.4.1 Connections via X-Windows

In the following discussion, we will assume that you need to do your computing on a computer called Server and that you are sitting in front of a workstation called MyHost.

If Server and MyHost are both on the same local area network and both have the same byte ordering, then they should have AIPS installed with both of them shown as being at the same AIPS “site.” In this case, you simply slogin, rlogin, or telnet into Server from a window on MyHost and issue the aips command as described in 2.2.3. The aips command will recognize that you are coming in from MyHost only if the $DISPLAY environment variable is correct (MyHost:0). In that case, or if you add tv=MyHost to the aips command line, the procedure will start the message, graphics, and TV servers on MyHost if needed. If you want to share data areas between the two computers, you may add a da=MyHost on the command line and AIPS will run with all data areas from both machines. (The disk systems must be auto-mountable between the two computers.) There are two verbs within AIPS which will allow you the equivalent of da=. They are ADDDISK which will add the disks of a selected computer to the current list of data disks and REMDISK which will remove the disks of a selected computer from the current list. The aips command also lets you select the most convenient printer within your local area network for use in your AIPS session. Other forms of data transfer, including magnetic tapes, will be discussed later.

If Server and MyHost have different byte orders or are not both on the same local area network, then they cannot be at the same AIPS site. If both machines have AIPS installed and the versions are compatible, then you may run on Server with MyHost treated as a “guest.” Again, slogin, rlogin, or telnet into Server from a window on MyHost. Make sure that the environment variable DISPLAY on Server is set to MyHost:0 and that Server is mentioned in your .rhosts file on MyHost. Then issue the usual aips command. You do not have to give the tv= option, but you may give tv=MyHost if you wish.. This will start the message, graphics, and TV servers on MyHost if needed. If the servers fail to start and messages such as “Cannot start remote TV servers” appear, then you must start the servers using the aips command on MyHost. The displays will work without restarting AIPS on Server. Thereafter, give the aips option tvok to Server (rather than tv=) to suppress the annoying messages. There is no drawback to being a guest TV; all catalogs and device information are now maintained by XAS itself. Since the display refreshing is handled locally by programs running in MyHost, this level of connection supports nearly full interactivity including such demanding displays as TVBLINK and TVMOVIE.

If MyHost does not have AIPS installed, then you may run the message, graphics, and TV servers on Server, with the X-Windows $DISPLAY set to MyHost:0. You may do this with internet sockets, but this ties up the one instance of the servers allowed to use such sockets. The socially acceptable method uses local Unix sockets so that only current AIPS session(s) on Server may talk to the windows in MyHost. You must ask for this explicitly, setting tv=local. This mode of operation is not encouraged since the display refreshing has to be transmitted over the network, making some of the interactive displays too slow to be useful. Nonetheless, there are circumstances in which this mode of operation is the only one available. You will have to add Server as an allowed X host (xhost +Server) to use this option. See HELP AIPS  C R for more information on “local” TVs which, among other things, allow for multiple TVs on a single display screen.

12.4.2 Connections to a terminal

You may do some interactive AIPSing if your workstation window is able to emulate a Tektronix 4010 terminal, or you are at a terminal capable of this emulation. (Note that most xterm displays may be switched between a “Tek mode” and the normal “VT mode” by pressing the Control key and the middle mouse button.) To operate in this mode, log in to Server from your terminal or workstation window and start AIPS with the command-line option REMOTE. This option will disable all TV functions, will cause all task messages to come to your terminal or window, and will cause any graphics (“TK”) displays to be sent to your terminal or window. You may display an “image” by creating a contour drawing with CNTR and then displaying the plot file with TKPL Interactive cursor verbs and procedures such as TKXY, TKPOS, and TKWIN may then be used. The old 4010 Tektronix display mixed plotting and text in a less than elegant fashion which is slavishly honored by most emulations. This is unfortunate, but usually does not prevent the display from being used for simple position selection and the like.

The AIPS task TXPL is a powerful tool for remote users without any, or correct, Tektronix 4010 emulation. It reads an extension file of type PL and translates the graphics commands in that file to an alphanumeric display for a “dumb” terminal. TXPL may be exactly what you need for AIPS applications that depend on scanning the shape of a plot rather than its fine detail. Common examples are viewing the shape of visibility functions produced by UVPLT (to guide self-calibration or to diagnose interference) or examining calibration solution plots from SNPLT. TXPL can also usefully interpret simple contour plots or even grey scales(!) for a remote user. It is often much faster to use TXPL to diagnose the state of your AIPS data processing over a low-bandwidth link than to use TKPL to execute a stream of Tektronix graphics instructions (even if you have full Tektronix 4010 emulation).

12.4.3 File transfer connections

The techniques discussed above apply to many computer configurations and to most tools within AIPS. They do not, however, handle the outputs of printing and plotting tasks. Nor do they provide much support for small computer systems that have no AIPS capability of their own. In such cases, the results of your computations will need to be written onto disk on Server and then transferred over the network to MyHost.

AIPS does not support remote printers explicitly. However, all AIPS tasks and verbs which generate printer output support the OUTPRINT adverb. With this adverb, you may specify a disk text file to receive the printer text. If you specify the same file for successive printer verbs or tasks, the outputs will be concatenated. (AIPS batch jobs do this automatically to concatenate all printer displays for the job.) You may then copy the text file to MyHost for editing, printing, or whatever. If you wish to print the whole file on a PostScript printer on MyHost, you may wish to run F2PS on the text file on Server and copy the result to MyHost. AIPS provides a “filter” program to convert plain (or Fortran) text files to PostScript for printing on PostScript printers. The command

$  F2PS -nn < file >  outfile

will convert text file file to PostScript format file outfile. The parameter nn is the number of lines per page used inside AIPS; use 97 for a small font in “portrait” form or 61 for a larger font in “landscape” form.

The AIPS task LWPLA also has an option to write its output to a disk file in encapsulated PostScript form using the OUTFILE parameter. Similarly, TVRGB and TVCPS use the same adverb to write PostScript text files containing their three-color displays. Numerous other AIPS tasks offer the option to write details of the operation to a text file specified with OUTTEXT. These include SLICE (slice), IMEAN (histogram), GAL (fit results), POSSM (spectrum), FRPLT (spectrum), HITEXT (history), UVCRS (uv-plane crossings), CONPL (convolving functions), etc.

FITS-disk files may be written with FITTP and FITAB and read with FITLD, UVLOD and IMLOD. For efficiency reasons, these are binary files rather than the text files produced by everything else. AIPS table files will have their contents transferred by these tasks along with the main data files. To put an AIPS table in a disk file in text form, use TBOUT to write a simple text file or EXTAB to write a file suitable for database and spreadsheet programs. Files in the form written by TBOUT may be read back into AIPS with TBIN.

To transfer the FITS-disk files and text files between MyHost and Server, some standard network file transfer must be used. For example, use ftp on MyHost with

%  cd MyArea  C R

to switch to the disk area on MyHost used for your files.

%  ftp Server  C R

to start ftp to the remote system.

Name (Server:):  loginame  C R

to log in to account loginame.

Password:  password  C R

to give the account’s password.

ftp>  cd  directory  C R

to change to the directory name containing the file on Server.

ftp>  binary  C R

to allow reading of a binary file — required for FITS-disk files, okay for text files.

ftp>  hash  C R

to get progress symbols as the copy proceeds — a good idea for large files.

ftp>  put  filename  C R

to send filename from MyHost to Server.

ftp>  get  anothername  C R

to send anothername from Server to MyHost.

ftp>  quit  C R

to exit from ftp.

The files should then be in the desired directories. You may have to rename them, however, to a name in all upper-case letters unless you use the “trick” mentioned in 3.10.1. The secure copy (scp) is preferable if you have a secure connection set up. The files may be compressed with gzip before copying and then uncompressed with gunzip at the other end. This is particularly effective on text files and images written by FITAB with quantization.