If you would like to restart varnish you will first need to test the configuration to make sure the restart does not stop the service:
\\
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Note: When you run the following command it should dump the output of the config on the screen if it is successful. If it fails then it will produce an error.
<sxh bash>
varnishd -C -f /etc/varnish/default.vcl
</sxh>
If succesfull then run:
<sxh bash>
service varnish reload
</sxh>
or
<sxh bash>
service varnish restart
</sxh>