Here is how to manually restart or stop Virtuoso from the command line.

The following article was used as a reference.

https://stackoverflow.com/questions/42575039/how-to-manually-restart-or-stop-virtuoso-from-commandline

The following approach seems to work well.

isql {host}:{port} {UID} {PWD} EXEC=shutdown

A specific example is as follows.

isql localhost:1111 dba dba EXEC=shutdown

If isql is not found as shown below, change the path and execute.

isql localhost:1111 dba dba EXEC=shutdown
bash: isql: command not found

find / -name isql
/usr/local/bin/isql
/root/virtuoso-opensource/binsrc/tests/isql

/usr/local/bin/isql localhost:1111 dba dba EXEC=shutdown

I hope this serves as a helpful reference.