If it hasn't changed since TeXLive 2009, you can set
in the configuration file. To find out which file to put that in, run
and you will see some output like this:
Configuration files are:
(*) absent /home/username/texmf/texdoc/texdoc.cnf
(*) This is the recommended configuration file for your personal preferences.
Put the line in the filename marked by the
(*), creating it if necessary.
EDIT: To add to the above explanation: according to the documentation (and again, this is for TeXlive 2009),
texdoc gets its configuration information from 5 sources.
- Command-line options (irrelevant for this question, since there's no CL option to set the viewer app)
- Environment variables ending with
PDFVIEWER_texdoc is the one that controls the PDF viewer.
Other environment variables. For the PDF viewer app, these are
The documentation isn't clear on which order they're checked in but
PDFVIEWER is the preferred alternative so I'd expect it to take precedence over the others.
- Values from configuration files, read in the order given by
- Hard-coded defaults (system-dependent)
Again, this is all explained in the documentation, which can be accessed by running