[SOLVED] ssh connection immediately disconnects after login

smoneck · 2018-02-06 16:23:07

Hi!

ssh connections to localhost/this machine immediately disconnect after successful login. I ran out of ideas ...

~ $ ssh -vvv user@localhost
OpenSSH_7.6p1, OpenSSL 1.1.0g  2 Nov 2017
debug1: Reading configuration data /home/user/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug2: resolving "localhost" port 22
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to localhost [127.0.0.1] port 22.
debug1: Connection established.
debug1: identity file /home/user/.ssh/id_rsa type 0
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_dsa-cert type -1
debug1: identity file /home/user/.ssh/id_ecdsa type 2
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_ed25519-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_7.6
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.6
debug1: match: OpenSSH_7.6 pat OpenSSH* compat 0x04000000
debug2: fd 3 setting O_NONBLOCK
debug1: Authenticating to localhost:22 as 'user'
debug3: hostkeys_foreach: reading file "/home/user/.ssh/known_hosts"
debug3: record_hostkey: found key type RSA in file /home/user/.ssh/known_hosts:31
debug3: load_hostkeys: loaded 1 keys from localhost
debug3: order_hostkeyalgs: prefer hostkeyalgs: ssh-rsa-cert-v01@openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa
debug3: send packet: type 20
debug1: SSH2_MSG_KEXINIT sent
debug3: receive packet: type 20
debug1: SSH2_MSG_KEXINIT received
debug2: local client KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1,ext-info-c
debug2: host key algorithms: ssh-rsa-cert-v01@openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa,ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ssh-ed25519-cert-v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519
debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,zlib@openssh.com,zlib
debug2: compression stoc: none,zlib@openssh.com,zlib
debug2: languages ctos:
debug2: languages stoc:
debug2: first_kex_follows 0
debug2: reserved 0
debug2: peer server KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1
debug2: host key algorithms: ssh-rsa,rsa-sha2-512,rsa-sha2-256
debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,zlib@openssh.com
debug2: compression stoc: none,zlib@openssh.com
debug2: languages ctos:
debug2: languages stoc:
debug2: first_kex_follows 0
debug2: reserved 0
debug1: kex: algorithm: curve25519-sha256
debug1: kex: host key algorithm: rsa-sha2-512
debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug3: send packet: type 30
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug3: receive packet: type 31
debug1: Server host key: ssh-rsa SHA256:vM0iIs76sA17my0/KFVqIeYAKs0OPnkpzL6JUL5hTyg
debug3: hostkeys_foreach: reading file "/home/user/.ssh/known_hosts"
debug3: record_hostkey: found key type RSA in file /home/user/.ssh/known_hosts:31
debug3: load_hostkeys: loaded 1 keys from localhost
debug1: Host 'localhost' is known and matches the RSA host key.
debug1: Found key in /home/user/.ssh/known_hosts:31
debug3: send packet: type 21
debug2: set_newkeys: mode 1
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug3: receive packet: type 21
debug1: SSH2_MSG_NEWKEYS received
debug2: set_newkeys: mode 0
debug1: rekey after 134217728 blocks
debug2: key: /home/user/.ssh/id_rsa (0x560f6eebe1b0)
debug2: key: /home/user/.ssh/id_dsa ((nil))
debug2: key: /home/user/.ssh/id_ecdsa (0x560f6eec0e10)
debug2: key: /home/user/.ssh/id_ed25519 ((nil))
debug3: send packet: type 5
debug3: receive packet: type 7
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521>
debug3: receive packet: type 6
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug3: send packet: type 50
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey,password
debug3: start over, passed a different list publickey,password
debug3: preferred 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 public key: RSA SHA256:IGFNgfWpkqx8oHdriKznB/XCiHtVmGeJlUcwLYBVBiU /home/user/.ssh/id_rsa
debug3: send_pubkey_test
debug3: send packet: type 50
debug2: we sent a publickey packet, wait for reply
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey,password
debug1: Trying private key: /home/user/.ssh/id_dsa
debug3: no such identity: /home/user/.ssh/id_dsa: No such file or directory
debug1: Offering public key: ECDSA SHA256:y52EXoTBSYR1wfOw9qxkpDfCXArHC7qovKuwir6wImk /home/user/.ssh/id_ecdsa
debug3: send_pubkey_test
debug3: send packet: type 50
debug2: we sent a publickey packet, wait for reply
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey,password
debug1: Trying private key: /home/user/.ssh/id_ed25519
debug3: no such identity: /home/user/.ssh/id_ed25519: No such file or directory
debug2: we did not send a packet, disable method
debug3: authmethod_lookup password
debug3: remaining preferred: ,password
debug3: authmethod_is_enabled password
debug1: Next authentication method: password
user@localhost's password:
debug3: send packet: type 50
debug2: we sent a password packet, wait for reply
debug3: receive packet: type 52
debug1: Authentication succeeded (password).
Authenticated to localhost ([127.0.0.1]:22).
debug1: channel 0: new [client-session]
debug3: ssh_session2_open: channel_new: 0
debug2: channel 0: send open
debug3: send packet: type 90
debug1: Requesting no-more-sessions@openssh.com
debug3: send packet: type 80
debug1: Entering interactive session.
debug1: pledge: network
debug3: receive packet: type 80
debug1: client_input_global_request: rtype hostkeys-00@openssh.com want_reply 0
debug3: receive packet: type 91
debug2: channel_input_open_confirmation: channel 0: callback start
debug2: fd 3 setting TCP_NODELAY
debug3: ssh_packet_set_tos: set IP_TOS 0x10
debug2: client_session2_setup: id 0
debug2: channel 0: request pty-req confirm 1
debug3: send packet: type 98
debug2: channel 0: request shell confirm 1
debug3: send packet: type 98
debug2: channel_input_open_confirmation: channel 0: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug3: receive packet: type 99
debug2: channel_input_status_confirm: type 99 id 0
debug2: PTY allocation request accepted on channel 0
debug2: channel 0: rcvd adjust 2097152
debug3: receive packet: type 99
debug2: channel_input_status_confirm: type 99 id 0
debug2: shell request accepted on channel 0
debug3: receive packet: type 96
debug2: channel 0: rcvd eof
debug2: channel 0: output open -> drain
debug2: channel 0: obuf empty
debug2: channel 0: close_write
debug2: channel 0: output drain -> closed
debug3: receive packet: type 98
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug3: receive packet: type 98
debug1: client_input_channel_req: channel 0 rtype eow@openssh.com reply 0
debug2: channel 0: rcvd eow
debug2: channel 0: close_read
debug2: channel 0: input open -> closed
debug3: receive packet: type 97
debug2: channel 0: rcvd close
debug3: channel 0: will not send data after close
debug2: channel 0: almost dead
debug2: channel 0: gc: notify user
debug2: channel 0: gc: user detached
debug2: channel 0: send close
debug3: send packet: type 97
debug2: channel 0: is dead
debug2: channel 0: garbage collecting
debug1: channel 0: free: client-session, nchannels 1
debug3: channel 0: status: The following connections are open:
  #0 client-session (t4 r0 i3/0 o3/0 fd -1/-1 cc -1)

debug3: send packet: type 1
Connection to localhost closed.
Transferred: sent 2740, received 2508 bytes, in 0.1 seconds
Bytes per second: sent 29041.7, received 26582.7
debug1: Exit status 0

Fresh /etc/ssh/sshd_config

AuthorizedKeysFile	.ssh/authorized_keys
ChallengeResponseAuthentication no
UsePAM yes
Subsystem	sftp	/usr/lib/ssh/sftp-server
ForceCommand /usr/local/bin/export_term

journalctl -x _COMM=sshd

Feb 06 17:20:39 computer sshd[19000]: Accepted password for user from 127.0.0.1 port 50332 ssh2
Feb 06 17:20:39 computer sshd[19000]: pam_unix(sshd:session): session opened for user user by (uid=0)
Feb 06 17:20:39 computer sshd[19002]: Received disconnect from 127.0.0.1 port 50332:11: disconnected by user
Feb 06 17:20:39 computer sshd[19002]: Disconnected from user user 127.0.0.1 port 50332
Feb 06 17:20:39 computer sshd[19000]: pam_unix(sshd:session): session closed for user user

Thanks a lot for any help!

P.s.: I also tried removing .profile, .bash_profile as well as an other login shell.

Last edited by smoneck (2018-02-06 22:21:17)

Trilby · 2018-02-06 16:35:08

smoneck wrote:

ssh connections to localhost/this machine ...

What? Why would you even try to do that?

I wasn't sure what to expect from such a nonsensical process, but I just confirmed I get similar results.

Is this an XY problem? Are you really trying to figure out why you can't log in to that machine from *other* machines? If so, provide the errors from those attempts. What you are showing is not out of the ordinary.

EDIT: from a quick search I see others expect this to work, so maybe something is wrong - but I still don't understand the purpose, and I'm not at all concerned about it failing on my machines (which can be shelled into quite readily from *other* machines).

Last edited by Trilby (2018-02-06 16:38:11)

smoneck · 2018-02-06 16:50:18

Yes, this might be a special case ...

Okay, the background in very short: I want to make a backup using borgbackup to a davfs2-mounted storage. This is not working due to reasons I'm currently investigating but I suspect the davfs2. I now want to slow the connection down and the only way I found is this inevitably invoking ssh. But since this is not a ssh-reachable storage, I try to ssh to localhost ... :Ü

Last edited by smoneck (2018-02-06 17:20:15)

seth · 2018-02-06 20:28:07

try to connect to "127.0.0.1" instead.

smoneck · 2018-02-06 21:19:37

seth wrote:

try to connect to "127.0.0.1" instead.

The same.

seth · 2018-02-06 21:23:57

Try w/o "ForceCommand /usr/local/bin/export_term"

loqs · 2018-02-06 21:24:01

Try stopping the sshd service and running sshd -vvv as root see if the output from the server side provides any insight.

smoneck · 2018-02-06 22:12:42

seth wrote:

Try w/o "ForceCommand /usr/local/bin/export_term"

Weeee that did it! What does that mean/indicate?

seth · 2018-02-06 22:13:33

What is /usr/local/bin/export_term? Seems some local script?

fukawi2 · 2018-02-06 22:14:01

seth wrote:

Try w/o "ForceCommand /usr/local/bin/export_term"

This would be my guess -- that script is being run and exits with success, at which point the connection is terminated because ForceCommand is completed.

smoneck · 2018-02-06 22:18:56

Interesting ... I don't remember to have written that.
Nevertheless it's content is just

#!/bin/bash
export TERM=xterm-256color

Thank you all very much for the help!

P.s.: Enjoy the view until the connection drops!

seth · 2018-02-06 22:22:55

See fukawi2's explanation.
Also exporting TERM to anything is NEVER a good idea - ssh or not.

smoneck · 2018-02-06 22:26:13

seth wrote:

Also exporting TERM to anything is NEVER a good idea - ssh or not.

Why is it so?

I often use it along ssh since my `xterm-termite` is never recognized on other machines.

Last edited by smoneck (2018-02-06 22:26:39)

seth · 2018-02-06 22:43:05

A false TERM variable can löead to all kinds of trouble, thus it's important to have the VTE set it, not the shell.
https://wiki.archlinux.org/index.php/Ho … ot_working

Oc, if you ever only use the same VTE for all times, that argument is kinda moot - except when the VTE at some point chooses a new TERM value and relies in that ... ;-)

Arch Linux

#1 2018-02-06 16:23:07

[SOLVED] ssh connection immediately disconnects after login

#2 2018-02-06 16:35:08

Re: [SOLVED] ssh connection immediately disconnects after login

#3 2018-02-06 16:50:18

Re: [SOLVED] ssh connection immediately disconnects after login

#4 2018-02-06 20:28:07

Re: [SOLVED] ssh connection immediately disconnects after login

#5 2018-02-06 21:19:37

Re: [SOLVED] ssh connection immediately disconnects after login

#6 2018-02-06 21:23:57

Re: [SOLVED] ssh connection immediately disconnects after login

#7 2018-02-06 21:24:01

Re: [SOLVED] ssh connection immediately disconnects after login

#8 2018-02-06 22:12:42

Re: [SOLVED] ssh connection immediately disconnects after login

#9 2018-02-06 22:13:33

Re: [SOLVED] ssh connection immediately disconnects after login

#10 2018-02-06 22:14:01

Re: [SOLVED] ssh connection immediately disconnects after login

#11 2018-02-06 22:18:56

Re: [SOLVED] ssh connection immediately disconnects after login

#12 2018-02-06 22:22:55

Re: [SOLVED] ssh connection immediately disconnects after login

#13 2018-02-06 22:26:13

Re: [SOLVED] ssh connection immediately disconnects after login

#14 2018-02-06 22:43:05

Re: [SOLVED] ssh connection immediately disconnects after login

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