quando eu quero conectar ao meu servidor assim

ssh -a [email protected] -p 22

isso me dá duas mensagens de erro:

PTY allocation request failed on channel 0
shell request failed on channel 0

quando eu uso o parâmetro-T a primeira mensagem de erro desaparece. Mas como consertar o segundo? Não consigo me conectar. Para outro servidor eu posso conectar sem problemas.

Estou no MAC OS 10.9 O parâmetro-v mostra-me esta saída de depuração:

OpenSSH_6.2p2, OSSLShim 0.9.8r 8 Dec 2011
debug1: Reading configuration data /etc/ssh_config
debug1: /etc/ssh_config line 20: Applying options for *
debug1: Connecting to xxx.your-server.de [188.40.3.15] port 22.
debug1: Connection established.
debug1: identity file /Users/xxx/.ssh/id_rsa type -1
debug1: identity file /Users/xxx/.ssh/id_rsa-cert type -1
debug1: identity file /Users/xxx/.ssh/id_dsa type -1
debug1: identity file /Users/xxx/.ssh/id_dsa-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.2
debug1: Remote protocol version 2.0, remote software version mod_sftp/0.9.8
debug1: no match: mod_sftp/0.9.8
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
debug1: kex: client->server aes128-ctr 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: Server host key: RSA 55:f5:ca:ca:01:45:0f:7b:71:0a:1f:ba:9e:25:17:fb
debug1: Host 'xxx.your-server.de' is known and matches the RSA host key.
debug1: Found key in /Users/xxx/.ssh/known_hosts:1
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
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: /Users/xxx/.ssh/id_rsa
debug1: Trying private key: /Users/xxx/.ssh/id_dsa
debug1: Next authentication method: password

depois de digitar a senha, recebo este

debug1: Authentication succeeded (password).
Authenticated to xxx.your-server.de ([xxx.xxx.3.15]:22).
debug1: channel 0: new [client-session]
debug1: Entering interactive session.
debug1: Sending environment.
debug1: Sending env LANG = de_DE.UTF-8
shell request failed on channel 0