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SCSxx05/SCSxx20 User Guide 8: Commands

8-13

Advanced Sysadmin Commands

You can access the following features from the command line interface or

administer them using a Linux command line prompt through your network.

Using ssh Keys and keygen Procedures

The following info is taken, with great liberties, from an open source article

discussing ssh and keygen. It is online at:

http://igloo.its.unimelb.edu.au/Webmail/security/msg00010.html.

ssh-agent: Type My Passphrase Once

Ssh-agent makes this all so easy. Basically, it loads my private key into memory once per

session, prompting me for a passphrase to decrypt the key at the time of load. At that

point, I can use this key as if it had no passphrase until I end that session or remove the

key from memory. Since it's never written to disk in its decrypted form, this is pretty darn

safe. Let's see this at work:

[max@miraclehut ~]$ ssh-agent /bin/bash

[max@miraclehut max]$ ssh-add

Need passphrase for /home/max/.ssh/identity (max@miraclehut).

Enter passphrase:

Identity added: /home/max/.ssh/identity (max@miraclehut)

[max@miraclehut jay]$ ssh humperdink@castle

In the first step, I invoke the ssh-agent, giving it a child program to run. The agent gives

access to my key(s) only to its children. I run bash here, so that every program I run in this

new bash shell can have access to my private key. I just as well could have typed "ssh-

agent xterm" or "ssh-agent startx" to give all programs run in a specific xterm or in X

session, respectively, this kind of access.

In the second step, I actually give the agent my key. I decrypt it once, by entering my

passphrase. I won't have to type my passphrase again until I quit bash.

Finally, in the third step, I ssh to my "humperdink" account on the "castle" host. As long as

I have set up that account properly, by appending this account's ~/.ssh/identity.pub to the

end of humperdink@castle ~/.ssh/authorized_keys file, I'll connect with no password

whatsoever! I can keep doing things like this over and over, using scp to copy files, ssh to

host. When I'm done, I can type exit to kill off the bash shell, and thus the agent.

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Lantronix SCS1620 Podręcznik Użytkownika Strona 100