Linux Mint 20.1
Apache Solr 8.11.1
I am able to post XML documents from the examples subdirectory such as ipod_other.xml, just not a simple, well formed HTML file I have added to that subdirectory in order to test Solr because I anticipate indexing HTML documents. (Note that this is my first Solr rodeo.)
~/dev/solr-8.11.1/example/exampledocs $ ../../bin/post -c gettingstarted sample.html
/home/russ/dev/jdk-11.0.10+9/bin/java -classpath /home/russ/dev/solr-8.11.1/dist/solr-core-8.11.1.jar -Dauto=yes -Dc=gettingstarted -Ddata=files org.apache.solr.util.SimplePostTool sample.html
SimplePostTool version 5.0.0
Posting files to [base] url http://localhost:8983/solr/gettingstarted/update...
Entering auto mode. File endings considered are xml,json,jsonl,csv,pdf,doc,docx,ppt,pptx,xls,xlsx,odt,odp,ods,ott,otp,ots,rtf,htm,html,txt,log
POSTing file sample.html (text/html) to [base]/extract
SimplePostTool: WARNING: Solr returned an error #404 (Not Found) for url: http://localhost:8983/solr/gettingstarted/update/extract?resource.name=%2Fhome%2Fruss%2Fdev%2Fsolr-8.11.1%2Fexample%2Fexampledocs%2Fsample.html&literal.id=%2Fhome%2Fruss%2Fdev%2Fsolr-8.11.1%2Fexample%2Fexampledocs%2Fsample.html
In server/solr/gettingstarted/conf/solrconfig.xml I have added:
<requestHandler name="/update" class="solr.UpdateRequestHandler" />
as suggested elsewhere, but this makes no difference in or out.
I am able to access http://localhost:8983/solr/#/ and http://localhost:8983/solr/#/gettingstarted/core-overview as well as run queries.