This is the only configuration file that must be present.
During installation, if LaTeX cannot find a file with this name
then a default file texsys.cfg, consisting entirely of comments, is
written out and used. Note that, until this file has been read,
LaTeX is not able to test reliably whether a given file exists on
the system.
The contents of the file texsys.cfg allow LaTeX to cope with
various differences between the behaviours of different TeX systems,
mainly in relation to file handling. The default version of this file
contains, in its comments, possible settings that may be needed for a
range of TeX systems. For more information, typeset the file
ltdirchk.dtx.
If you have copied your LaTeX installation from a computer that
used a different operating system then you may well have a version of
texsys.cfg that will make it difficult to install LaTeX on your
system. If this happens then start the process again with an empty
texsys.cfg file; this will produce an installation that should, at
least, allow you to typeset the documentation. However, it is
possible that LaTeX can still find only those files that are in the
current directory; in this case you must set the macro \input@path
correctly for your system.