刚才显示有一个插件更新，于是我试着点了一下更新，可能是网速原因，更新了几分钟还没好，于是我就没有耐心了，试着刷新页面让它停止。结果网页上显示：Briefly unavailable for scheduled maintenance. Check back in a minute.可以猜得出是wordpress的原因，试着在百度上搜了一下这个错误。进了一个外国网站，英文很友好，一下就看懂了。解决方案是通过ftp软件进入网站根目录删除.maintenance文件,如图，删除成功就ok啦。
顺便附上原文：

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How To Fix: Briefly unavailable for scheduled maintenance. Check back in a minute.

If you have recently done some upgrade work on your WordPress site, and you cannot login due to the following message, I have the fix for you.

Briefly unavailable for scheduled maintenance. Check back in a minute.

What Causes This Problem

This problem is caused by a failed automatic update on one or more parts of your WordPress site.
When WordPress is automatically updating the core WordPress files, plugins or themes, your site is marked as under maintenance.
This problem occurs when the under maintenance is not marked as done at the end of the process.  This can be caused by an interrupted update, the updating taking so long that it times out or browser crashes.

How To Fix It

Fortunately the fix is fairly simple, you need to attach to your site using ftp or with the file manager in your hosting account, and in the root of your installation you will see a file called .maintenance, simply delete this file and you site will come back to life.

SPECIAL NOTE: files which start with a full stop/period are marked as hidden files on unix/linux, you may need to enable show hidden files on your FTP client before you can see this file, for example on filezilla you need to go to server->force show hidden files.

If At First You Don’t Succeed

Once you have deleted the .maintenance file it is a good idea to re-apply the updates you were doing to make sure they have been completed correctly.