10. Installation Troubleshooting

Interchange uses the services of other complex programs, such as Perl, Web servers, and relational databases, to work. Therefore, when there is a problem, check these programs before checking Interchange. Many more basic installation problems have to do with those than with Interchange itself.

If an error message is received about not being able to find libraries, or a core dump has occurred, or a segment fault message, it is always an improperly built or configured Perl. Contact the system administrator or install a new Perl.

The makecat program is intended to be used to create the starting point for the catalog. If the demo does not work the first time, keep trying. If it still does not work, try running in INET mode.

Check the two error log files: error.log in the Interchange home directory (where interchange.cfg resides) and error.log in the catalog directory (where catalog.cfg resides; there can be many of these). Many problems can be diagnosed quickly if these error logs are consulted.

Check the README file, the FAQ, and mail list archive at the official Interchange web site for information:


Double check the following items:

  1. Using UNIX sockets?
    • Check that the vlink program is SUID, or the appropriate changes have been made in the SocketPerms directive. Unless the files are world-writable, the vlink program and the Interchange server must run as the same user ID! If running CGI-WRAP or SUEXEC, the vlink program must not be SUID.
    • If having trouble with the vlink program (named construct in the demo configuration), try re-running makecat and using INET mode instead. (Or copy the tlink INET mode link program over vlink). This should work unchanged for many systems.
    • If using an ISP or have a non-standard network configuration, some changes to interchange.cfg are necessary. For tlink to work, the proper host name(s) must be configured into the TcpHost directive in interchange.cfg. The program selects port 7786 by default (the ASCII codes for "M" and "V", for MiniVend). If another port is used, it must be set to the same number in both the tlink program (by running compile_link) and the interchange.cfg file. The tlink program does not need to be SUID.
  2. Proper file permissions?
    • The Interchange server should not run as the user nobody! The program files can be owned by anyone, but any databases, ASCII database source files, error logs, and the directory that holds them must be writable by the proper user ID, that is the one that is executing the Interchange program.
    • The best way to operate in multi-user, multiple catalog setups is to create a special interch user, then put that user in the group that contains each catalog user. If a group is defined for each individual user, this provides the best security. All associated files can be in 660 or 770 mode. There should be no problems with permissions and no problems with security.
  3. Is the vlink program being executed on a machine that has the socket file etc/socket on a directly attached disk?
    • UNIX-domain sockets will not work on NFS-mounted file systems! This means that the Interchange server and the CGI program vlink must be executing on the same machine.
    • The tlink program does not have this problem, but it must have the proper host name(s) and TCP ports set in the TcpHost and TcpMap directives in interchange.cfg. Also, be careful of security if sensitive information, like customer credit card numbers, is being placed on a network wire.