openssh

On Using Alternate Ports for SSH

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There’s a post I read the other day that’s really been stuck in my craw (link is below). It was about the effects of moving SSH to an alternate port. The post starts out like this: Best practices state that you should run ssh on an non-standard port. Unfortunately some programs use port 22 by default and it isn’t obvious what the switch is to change this port. First, whose best practices say this? Some self-appointed security expert on the web? I ask because this sort of activity is known as “security through obscurity” and isn’t regarded well as a security tactic. The Wikipedia article on security through obscurity has a section called “Arguments For” which reads more like an …

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SSH Escape Sequences (aka Kill Dead SSH Sessions)

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Did you know that when you’re using OpenSSH from the command line you have a variety of escape sequences available to you? SSH somewhere, then type “~” and “?” (tilde, then question mark) to see all the options. You should get something like: Supported escape sequences:   ~.  – terminate connection (and any multiplexed sessions)   ~B  – send a BREAK to the remote system   ~C  – open a command line   ~R  – Request rekey (SSH protocol 2 only)   ~^Z – suspend ssh   ~#  – list forwarded connections   ~&  – background ssh (when waiting for connections to terminate)   ~?  – this message   ~~  – send the escape character by typing it twice Most …

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Keep SSH Sessions From Disconnecting

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With the installation of new firewalls at work I’ve been getting disconnected a lot from hosts I SSH to, due to changes in the inactivity timeouts. It’s particularly inconvenient when I’m tailing a log that hasn’t changed in a while… and then the connection dies, and I don’t notice. Oops. It also happens in various other situations, like NAT through a home router, too. Let the connection sit for a while and you’ll have to recreate it. I could ask our network guys to change the timeouts, but it turns out there’s a better fix from the client side. SSH protocol version 2 supports server keepalive, essentially NOOPs sent to the server to keep the connection up. You can do …

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