You should ensure that your SP's copy of the MIT metadata is kept up to date. The current metadata is available in http://web.mit.edu/touchstone/shibboleth/config/metadata/MIT-metadata.xml.
The easiest way to maintain the metadata is via a cron job which runs a script to download and install the latest metadata. A sample of such a script is available in http://web.mit.edu/touchstone/shibboleth/config/metadata/update-metadata.sh-example. Adjust it as necessary for your installation; in particular, if you did not install from the stock RPMs from Internet2, you will need to adjust the setting for the Shibboleth etc directory at the top of the script.
The Shibboleth SP software detects and loads the updated metadata automatically; there is no need to restart the web server or shibd.
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