磁盘“Seagate”没有被推出，因为一个或多个程序可能正在使用它。

推出移动硬盘失败，解决方案：

1. 执行 lsof /Volumes/Seagate/ 可以看到哪些进程在占用磁盘

$ lsof /Volumes/Seagate/
COMMAND    PID  USER   FD   TYPE DEVICE SIZE/OFF   NODE NAME
QuickLook 1281 hangj    7r   REG   1,11   806150 396515 /Volumes/Seagate/a/b/c.docx

2. 打开活动监视器 Activity Monitor，找到 QuickLook，强制退出，或者执行下面的命令

$ lsof /Volumes/Seagate/ | grep -v PID | awk '{ print $2 }' | xargs kill -9

如果 lsof /Volumes/Seagate/ 没有输出的话，加上 sudo 再执行 sudo lsof /Volumes/Seagate/，估计会发现是 mds 和 mds_store 在后台搞鬼, 这两个是 SpotLight 的进程，强退之！

参考链接：
https://mycyberuniverse.com/macos/how-fix-volume-cant-be-ejected-because-currently-use-user.html
https://serverfault.com/questions/159422/os-x-determine-which-application-is-accessing-a-hdd-and-preventing-ejection

After some investigation I found that in my case this is the QuickLook process. The QuickLook process is a feature that was introduced in the Mac OS X 10.5 Leopard. You can learn more about it here. I noticed that when I use the Quicklook feature to preview a video in any format, the process keeps active even when the Quicklook window was already closed. If I preview any other file like PDF or JPG the disk can be ejected normally. Why does Quicklook preventing me from ejecting my disk? I suspect that this is just a bug.

还是不行的话，就退出登录，然后再登录进来。
还是不行的话，重启电脑吧