8
1
First of all, I've checked all the following
- Agent Forwarding not working
- Extra configuration required for ssh-agent forwarding?
- SSH Agent Forwarding Not Working
- https://serverfault.com/questions/404447/why-is-ssh-agent-forwarding-not-working
- https://apple.stackexchange.com/questions/37184/ssh-a-doesnt-properly-enable-forwarding-of-authentication-agent-connection
but none of them helped. So, here is my question:
I can ssh from A to B, or from A to C, but not from A to B, then B to C. When connecting from A to either B or C, I always use ssh -A
to force SSH Agent Forwarding.
But why I'm still not able to connect A -> B -> C
without being asked for passphrase?
UPDATE: nearly three years later, the same problem still haunts me, but now I've narrowed down the problem a bit:
Symptom: I can ssh A -> B
, or A -> C
, but not A -> B -> C
, or A -> C -> B
.
The problem is exactly described by the topic -- SSH Agent Forwarding is not working.
From
Troubleshoot SSH issues
https://confluence.atlassian.com/bitbucket/troubleshoot-ssh-issues-271943403.html
it says:
To list your loaded keys, enter
ssh-add -l
. If you don't see the SSH key you want to use...
then there is problem -- the SSH key you want to use is NOT loaded.
This is what's happening when I'm at A -> B
or A -> C
. I.e., right after I did ssh -A
into an intermediate server. the SSH key is lost, not forwarded and not loaded.
$ ssh-add -l
The agent has no identities.
That's the reason why I cannot ssh further without the passphrase.
It does have SSH_AUTH_SOCK
variable setup and several ssh-agent
around though:
$ echo "$SSH_AUTH_SOCK"
/tmp/ssh-RtEuLOmFDBet/agent.3722
$ ps -e | grep [s]sh-agent
3723 ? 00:00:00 ssh-agent
4613 ? 00:00:00 ssh-agent
It does not seem to be related to my own environment as they are identical, or the /etc/ssh/sshd_config
file, as I've compared the ones from the intermediate servers that are working or not working.
UPDATE END.
More info: all three machines, are configured with the standard Ubuntu ssh configuration. I.e., the AllowAgentForwarding
option is not in /etc/ssh/sshd_config
, though I doubt whether it should, because I saw "Since agent forwarding defaults on, it should be enough to remove any AllowAgentForwarding line from sshd_config." from Extra configuration required for ssh-agent forwarding?.
Some say ssh-add
will do, but when I do it on B or C, it asks me to Enter passphrase for
my .ssh/id_rsa
. Some say check the SSH_AUTH_SOCK
, but I do have it on B or C (either from A to B, or from A to C):
$ env | grep SSH_AUTH_SOCK
SSH_AUTH_SOCK=/tmp/ssh-RTScJ5PZh9Mh/agent.2083
Is the Agent Forwarding not working because of missing the AllowAgentForwarding
option ? Then which one (A, B, or C) should I put it in? Wouldn't ssh -A
be enough? Also I have the
.ssh/id_rsa
files on both B and C, is that the reason ssh-add
ask for the passphrase for them?
EDIT:
Here is the log of -Avvv
from B to C:
OpenSSH_6.2p2 Ubuntu-6ubuntu0.1, OpenSSL 1.0.1e 11 Feb 2013
debug1: Reading configuration data /home/myid/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to boxc.
debug1: Connection established.
debug3: Incorrect RSA1 identifier
debug3: Could not load "/home/myid/.ssh/id_rsa" as a RSA1 public key
debug1: identity file /home/myid/.ssh/id_rsa type 1
debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-1024
debug1: Checking blacklist file /etc/ssh/blacklist.RSA-1024
debug1: identity file /home/myid/.ssh/id_rsa-cert type -1
debug3: Incorrect RSA1 identifier
debug3: Could not load "/home/myid/.ssh/id_dsa" as a RSA1 public key
debug1: identity file /home/myid/.ssh/id_dsa type 2
debug1: Checking blacklist file /usr/share/ssh/blacklist.DSA-1024
debug1: Checking blacklist file /etc/ssh/blacklist.DSA-1024
debug1: identity file /home/myid/.ssh/id_dsa-cert type -1
debug1: identity file /home/myid/.ssh/id_ecdsa type -1
debug1: identity file /home/myid/.ssh/id_ecdsa-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.2p2 Ubuntu-6ubuntu0.1
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.2p2 Ubuntu-6
debug1: match: OpenSSH_6.2p2 Ubuntu-6 pat OpenSSH*
debug2: fd 3 setting O_NONBLOCK
debug3: put_host_port: boxc
debug3: load_hostkeys: loading entries for host "boxc" from file "/home/myid/.ssh/known_hosts"
debug3: load_hostkeys: found key type RSA in file /home/myid/.ssh/known_hosts:15
debug3: load_hostkeys: loaded 1 keys
debug3: order_hostkeyalgs: prefer hostkeyalgs: ssh-rsa-cert-v01@openssh.com,ssh-rsa-cert-v00@openssh.com,ssh-rsa
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug2: kex_parse_kexinit: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: ssh-rsa-cert-v01@openssh.com,ssh-rsa-cert-v00@openssh.com,ssh-rsa,ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,ssh-dss-cert-v00@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-dss
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se
debug2: kex_parse_kexinit: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: zlib@openssh.com,zlib,none
debug2: kex_parse_kexinit: zlib@openssh.com,zlib,none
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit: first_kex_follows 0
debug2: kex_parse_kexinit: reserved 0
debug2: kex_parse_kexinit: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se
debug2: kex_parse_kexinit: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,zlib@openssh.com
debug2: kex_parse_kexinit: none,zlib@openssh.com
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit: first_kex_follows 0
debug2: kex_parse_kexinit: reserved 0
debug2: mac_setup: found hmac-md5-etm@openssh.com
debug1: kex: server->client aes128-ctr hmac-md5-etm@openssh.com zlib@openssh.com
debug2: mac_setup: found hmac-md5-etm@openssh.com
debug1: kex: client->server aes128-ctr hmac-md5-etm@openssh.com zlib@openssh.com
debug1: sending SSH2_MSG_KEX_ECDH_INIT
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: RSA ed:26:20:93:4c:88:ef:17:70:e3:d4:7a:42:4c:8e:69
debug3: put_host_port: [192.168.2.122]:21
debug3: put_host_port: boxc
debug3: load_hostkeys: loading entries for host "boxc" from file "/home/myid/.ssh/known_hosts"
debug3: load_hostkeys: found key type RSA in file /home/myid/.ssh/known_hosts:15
debug3: load_hostkeys: loaded 1 keys
debug3: load_hostkeys: loading entries from file "/home/myid/.ssh/known_hosts"
debug3: load_hostkeys: found key type RSA in file /home/myid/.ssh/known_hosts:16
debug3: load_hostkeys: loaded 1 keys
debug1: Host 'boxc' is known and matches the RSA host key.
debug1: Found key in /home/myid/.ssh/known_hosts:15
debug1: ssh_rsa_verify: signature correct
debug2: kex_derive_keys
debug2: set_newkeys: mode 1
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug2: set_newkeys: mode 0
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug2: key: /home/myid/.ssh/id_rsa (0x7f7e....e760),
debug2: key: /home/myid/.ssh/id_dsa (0x7f7e....e7a0),
debug2: key: /home/myid/.ssh/id_ecdsa ((nil)),
debug1: Authentications that can continue: publickey
debug3: start over, passed a different list publickey
debug3: preferred gssapi-keyex,gssapi-with-mic,publickey,keyboard-interactive,password
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /home/myid/.ssh/id_rsa
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Server accepts key: pkalg ssh-rsa blen 149
debug2: input_userauth_pk_ok: fp 22:32:...:1d:e3
debug3: sign_and_send_pubkey: RSA 22:32:...:1d:e3
debug1: key_parse_private_pem: PEM_read_PrivateKey failed
debug1: read PEM private key done: type <unknown>
Enter passphrase for key '/home/myid/.ssh/id_rsa':
I've compared with my good session (A->C), and found all are none different, other than the last 3 lines, which starts with "key_parse_private_pem: PEM_read_PrivateKey failed
". The good session instead has:
debug1: Enabling compression at level 6.
debug1: Authentication succeeded (publickey).
Authenticated to boxc
Everything else are the same.
Again, my environment:
$ apt-cache policy openssh-server
openssh-server:
Installed: 1:6.2p2-6ubuntu0.1
Candidate: 1:6.2p2-6ubuntu0.4
Version table:
1:6.2p2-6ubuntu0.4 0
500 http://archive.ubuntu.com/ubuntu/ saucy-updates/main amd64 Packages
1:6.2p2-6ubuntu0.3 0
500 http://security.ubuntu.com/ubuntu/ saucy-security/main amd64 Packages
% sshd -v
sshd: illegal option -- v
OpenSSH_6.2p2 Ubuntu-6ubuntu0.1, OpenSSL 1.0.1e 11 Feb 2013
Thanks
Have you tried
ssh -Avv
(or maybe more-v
, I don't know the maximum verbosity level by heart) and watched the output? – ua2b – 2014-11-15T01:58:39.973yeah, I tried, with 4 v's. But don't know what to look for especially, and found nothing suspicious... Edit: Hold on, found something... – xpt – 2014-11-15T02:21:32.427
1So you
ssh-add
your key on A,ssh-add -l
shows the key has been loaded, then you log into B usingssh -A
. Doesssh-add -l
still show the same key? You don't need (the same key in).ssh/id_rsa
on B. I assume, your key is encrypted with the password that works well if you enter it at the prompt that you don't want to see? – ua2b – 2014-11-15T04:17:27.697Yes, all your sayings apply well to me, except that, on B,
ssh-add -l
does not show the same key any more. In fact I gotThe agent has no identities
. Also I do have the same key in.ssh/id_rsa
on B. Thanks again! – xpt – 2014-11-15T15:06:21.277