The sys admin's daily grind: Mosh
Shell on the Beach
Dangling your legs in the sea while enjoying the Mediterranean sunshine can affect the prospect of a good Internet connection; fortunately, Charly knows what to do.
I am writing this column on the Costa Brava and currently dangling my feet in the Med. This stretch of coast is aptly named; "brava" can be translated as "wild, inhospitable." Unfortunately, this description also applies to Internet coverage beyond the tourist beaches – although WiFi is ubiquitous in hotels, campsites, and bars. At the moment, I'm using a network operated by the "Xiringuito" beach bar near the picturesque ruins of the ancient Greek trading exclave of Empúries, and the connection is pretty brava.
This situation is not going to spoil the sunny afternoon for me, however, because I still have Mosh [1] stashed away as an ace in my beach bag. The SSH replacement consists of a client component and a server component along with a wrapper script. Initially, Mosh connects the client and server via SSH on port 22 in the normal way. Then, the server hands the client a key, with which it identifies itself henceforth, and Mosh drops the TCP connection.
At this point, the client and server talk only on UDP, using a port in the range between 60000 and 61000 by default. I can use the --port=<Portnumber> parameter to force Mosh to prefer a specific port. UDP connections are very robust; they even survive client suspend phases.
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