/etc/fstab 中第 5 和第 6 列的那两个数字是什么意思呢？

简单的说，第5个参数说该盘需要用dump备份，第6个参数说fsck检查磁盘的时候是最优先的级别(数字越小级别越高，但0为忽略）。

http://www.tuxfiles.org/linuxhelp/fstab.html

< 5th and 6th columns: Dump and fsck options >

Dump and, uh, what options? Well, dump is a backup utility and fsck is a filesystem check utility. I won't discuss them in great length here (they would both need their own tuXfile), but I'll mention them, because otherwise you'd spend the rest of the day wondering what on God's green Earth do these things mean.

The 5th column in /etc/fstab is the dump option. Dump checks it and uses the number to decide if a filesystem should be backed up. If it's zero, dump will ignore that filesystem. If you take a look at the example fstab, you'll notice that the 5th column is zero in most cases.
The 6th column is a fsck option. fsck looks at the number in the 6th column to determine in which order the filesystems should be checked. If it's zero, fsck won't check the filesystem. "