Vaguely recent versions of OpenSSH have a feature where you can havemultiple independent sessions running over what is actually oneconnection, even though you ran several separate ssh commands. Theprimary advantage this offers is that new ssh sessions startsignificantly faster, since they don't have to go through all of thecryptography and authentication of a full ssh connection. (As a sidebenefit, there's fewer processes running on either side, since you nolonger need a ssh and an sshd for each active session.)

When

Here is one of the general rules for Internet software:

You cannot count on other people not screwing up.

(You can barely count on you not screwing up.)

Any time you talk to the Internet, you have to assume that someday,the other end will do something that it isn't supposed to by thespecification. People are endlessly creative, which means that sooneror later someone will get pretty much anything wrong that it's possibleto get wrong; for example, they will use permanent HTTP

One of the things that I wish Linux package managers like yum and Apthad was a convenient way of retrieving the original, stock version ofsome file and optionally reinstalling it into its original place. I'dexpect (and wouldn't mind) that this would require re-downloading theoriginal package that the file came from (and thus it was restrictedto packages that were still in the package repository and hadn't beenobsoleted and removed by some more recent package).

You might wonder what use this