FD 4 is where things get a bit more interesting, since it is a write-only handle to a character device, essentially /dev/log.

FD 4 中的内容比较有趣，因为它是一个字符设备的只读句柄，实质上是 /dev/log。

youdao

The only Write operation permitted on a flash memory device is to change a bit from a one to a zero.

flash内存设备中惟一允许的Write操作是将1修改为0。

youdao