Koha has a cgi-bin/tools/export.pl file which allows you to export to MARC (or xml) format.

To run that manually, you will need to set the path for PERL5LIB (or whatever your perl lib variable is), and set the variable that points to the Koha configuration file. They will look something like:

export PERL5LIB=/usr/share/koha/lib:$PERL5LIB
export KOHA_CONF=/etc/koha/sites/library/koha-conf.xml

To do the export, you will want to do something like this (the paths may differ)

/usr/share/koha/bin/export_records.pl --format=xml  --filename="koha.xml"

Alternatively, you can use OAI-PMH or the web interface to export records; see Exporting Records from Koha for details.

Once you have exported the koha records, you will need to import the records into VuFind®.

Copy your marc_local.properties from vufind/install to the vufind/local/install directory. make the changes to this file that you need to

#collection = ""
institution = "My University"
#building = "Library A"
id = 999c, first

Koha needs to use the id = 999c for VuFind® to properly tie the two together. The id= field is not in every version of the marc_local.properties file, so you may need to add that manually.

Now you are ready to run the import.

See the How to index Koha with VuFind® page for a full end-to-end example.