Tyler Chris - Fedora Linux стр 46.

$ ssh-add

Enter passphrase for /home/jon/.ssh/id_dsa:

BigSecret

Identity added: /home/jon/.ssh/id_dsa (/home/jon/.ssh/id_dsa)

If you're not logged in to your Fedora system through the GUI, you will need to enter this command before using ssh-add :

$eval $(ssh-agent)

Agent pid 15431

When you log in using the GUI, Fedora starts the ssh-agent program automatically.

$ ssh jon@remoteMachine

Last login: Wed Oct 26 00:20:29 2005 from toronto-office

If you wish to run just a single command, you can enter it on the ssh command line instead of logging in:

$ ssh jon@remoteMachinecal 3 1967

March 1967

Su Mo Tu We Th Fr Sa

1 2 3 4

5 6 7 8 9 10 11

12 13 14 15 16 17 18

19 20 21 22 23 24 25

26 27 28 29 30 31

4.10.1.2. Using graphical applications remotely

$ ssh -C -X jon@10.0.0.1

Last login: Wed Oct 26 00:31:42 2005 from parisoffice

$

oowriter

In order for this to work, the remote host must have X11Forwarding set to yes in its /etc/ssh/sshd_config file.

The -X option may cause remote X clients to be counted as untrusted from the point of view of the X server. This is perfect for most purposes, but if you want the remote client to be able to do screen captures (for example, if the remote application is the GIMP and you want to acquire a screenshot), substitute -Y for -X to configure the remote client as trusted .

4.10.2. How Does It Work?

Public-key authentication relies upon the fact that two extremely large numbersthe public key and private key , which are derived mathematically from a single large random number, can be used with cryptographic formulas to encrypt and decrypt data. Anything encrypted with the public key can be decrypted only with the private key (not with the public key or any other number), and anything encrypted with the private key can be decrypted only with the public key. If the private key is kept secret and the public key is distributed to the whole world, then any message that can be decrypted by the public key must have been encrypted with the private key, proving the identity of the sender ( authentication ); any message that is encrypted with the public key can only be decrypted by the private key, ensuring secrecy ( authorization ).

In the case of SSH, the ssh-keygen command generates a public/private key pair, placing the private key in ~/.ssh/id_dsa and the public key in ~/.ssh/id_dsa.pub . When the public key is copied to the remote machine and placed in ~/.ssh/authorized_keys , an access request encrypted with the private key can be authenticated using the public key. If the public key is protected with a passphrase, you will be prompted for it each time you connect to a remote machine; to reduce this burden, the ssh-agent program can store your passphrase for you. The ssh-add command prompts you for your passphrase(s) and hands them over to ssh-agent (which is run automatically when the GUI starts up).

SSH is very susceptible to man-in-the-middle attacks, where a system between the client and server intercepts communication and presents itself as the client to the server, and the server to the client. However, this type of attack is a lot harder to set up than it would first appear and is rarely encountered. The caching of the host key (presented onscreen in summary format as the fingerprint ) guards against this after the first contact between the client and server systems has been made.

4.10.3. What About...

4.10.3.1. ...compressing data?

$ ssh -C jon@10.0.0.1

4.10.3.2. ...connecting to a Fedora system from a Windows system using SSH?

4.10.3.3. ...connecting to a Fedora system from a Mac OS X system?

4.10.3.4. ...connecting to my home system from another location?

to your Fedora system. Then you can connect to the Fedora system by specifying the address of the gateway system in the ssh client arguments.

For example, if the external IP address of the gateway is 1.2.3.4, and the LAN IP address of your Fedora system is 10.0.0.1, configure the router to pass incoming connections on TCP/IP port 22 to 10.0.0.1, and then use the gateway IP address in the client arguments:

$ ssh jon@1.2.3.4

You may also need to configure Fedora's firewall to permit SSH connections.

4.10.3.5. ...using public/private keys without a passphrase?

4.10.4. Where Can I Learn More?

The manpages for ssh , sshd , ssh_config , sshd_config , ssh-agent , ssh-add , and ssh-keygen

4.11. Using Shell Redirection and Piping

4.11.1. How Do I Do That?

standard input (stdin, file descriptor 0)

The normal input to the program

standard output (stdout, file descriptor 1)

The normal output from the program

standard error (stderr, file descriptor 2)

Error messages from the program

By default, these file descriptors are connected to the terminal, if one is available, so standard input comes from the terminal keyboard, and standard output and standard error go to the terminal screen. Programs may open any other connections they need to read or write files, communicate with other local programs, or communicate with programs over the network.