2012 macpro 升级 macos 到 10.15.2 catalina 并 安装 新xcode时碰到下列问题，供其他碰到的同学参考。
- 问题1. “macOS Catalina” could not be verified， 在”系统偏好设置 ” -> “软件更新”下下载完catalina更新包后点安装，提示 “macOS Catalina” could not be verified.
解决办法：打开“ 系统偏好设置”->“日期与时间”->去掉打勾”自动设置日期与时间”, 重启机器，并再次软件更新并安装。
Go to settings then date&time. Click and then unclick “set date and time automatically”. Save the changes by clicking the lock.
Then restart the computer and proceed to download the update once again through settings and software update. It resolved the issue of the update not being verified.
- 问题2. macos catalina安装完，打开xcode时，提示“An unknown error occurred. See the install log for more details.”
解决方法：
- 这个问题再次在Xcode 11.1出现，是有个证书在2019年的10月份某天过期引起的。
- 你可以通过暂时把系统日期修改到过期的日期之前来解决。
- 在Xcode 11这个版本下，设置系统日期为2019年10月3日，然后运行Xcode，再安装组件，（就可以安装成功了），完成之后再把系统日期改回正常状态。
- This problem has once again appeared in Xcode 11.1 and is caused by an invalid certificate that expired some day in October 2019.
- You can work around the problem by temporarily changing the system date to before the certificate expiration date.
- In the case of Xcode 11, set the system date to Oct 3, 2019, run Xcode, then change the date back after the components have installed.
苹果公司就这么把版本放出来也是醉了！
