Most maintenance plugins don’t work smoothly with WordPress multisite networks, but I found one that I’d like to recommend. WPMS Site Maintenance Mode was actually made just for multisite. It allows the super admin to put the entire network, main site, or subsites into maintenance mode. There’s also an option to customize the appearance of the maintenance page and set a time for the site to return.
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Check out the settings page:
Once you turn it on you’ll get something like this:
I tested WPMS Site Maintenance Mode this weekend and I’d recommend this WordPress multisite plugin to any network admin who needs a quick way to bring the stie(s) down for a few updates. Download it for free from the WordPress plugin repository.