Um euch das ganze mal praktisch zu erläutern habe ich mich mal zu einem Server per SSH verbunden.
user@linux:~$ ssh root@SERVER -v
OpenSSH_4.2p1 Debian-7ubuntu3.1, OpenSSL 0.9.8a 11 Oct 2005
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to SERVER [192.168.10.249] port 22.
debug1: Connection established.
debug1: identity file /home/user/.ssh/identity type -1
debug1: identity file /home/user/.ssh/id_rsa type -1
debug1: identity file /home/user/.ssh/id_dsa type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_4.2p1 Debian-8
debug1: match: OpenSSH_4.2p1 Debian-8 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_4.2p1 Debian-7ubuntu3.1
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-cbc hmac-md5 none
debug1: kex: client->server aes128-cbc hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host 'SERVER' is known and matches the RSA host key.
debug1: Found key in /home/user/.ssh/known_hosts:2
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Trying private key: /home/user/.ssh/identity
debug1: Trying private key: /home/user/.ssh/id_rsa
debug1: Trying private key: /home/user/.ssh/id_dsa
debug1: Next authentication method: password
root@SERVER's password:
debug1: Authentication succeeded (password).
debug1: channel 0:
new [client-session]
debug1: Entering interactive session.
debug1: Sending environment.
debug1: Sending env LANG = de_DE.UTF-8
Last login: Wed May 30 14:42:49 2007 from user.linuxnet.de
Linux SERVER 2.6.15-1-686-smp #2 SMP Mon Mar 6 15:34:50 UTC 2006 i686
The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.
Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
SERVER:~#
SERVER:~# logout
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: channel 0: free: client-session, nchannels 1
Connection to SERVER closed.
debug1: Transferred: stdin 0, stdout 0, stderr 28 bytes in 213.2 seconds
debug1: Bytes per second: stdin 0.0, stdout 0.0, stderr 0.1
debug1: Exit status 0
user@linux:~$
Im rot markierten Text wird die lokale Konfigurationsdatei ausgelesen und die Verbindung per TCP hergestellt. Das austauschen der Versionsnummern erfolgt(blau). Danach erfolgt der Vergleich der Protokollversionen(grün). Im schwarz markiertem Text werden zuerst die Authentifizierungsmethoden aufgelistet. Dabei schlägt die RSA-Authentifizierung fehl, deshalb wird die Passwort Authentifizierung ("debug1: Next authentication method: password") gewählt. Ist diese erfolgreich wird eine neue Session generiert ("new [client-session]").
Der orange markierte Text zeigt das schließen der Session, das man mit dem Befehl "logout" oder "exit" erreicht.
Nun habt ihr einen groben Überblick, wie SSH abläuft.
