I am using a fuse/sshfs mount which worked fine so far. Now I had to reinstall the server system and suddenly getting the classic read: Connection reset by peer error. I am using public key authentication and copied my key to the newly installed system. Normal ssh login works fine. I changed the log to debug but sadly this doesn't give me any useful information:

sshd[2077]: debug1: Forked child 2198.

sshd[2198]: Set /proc/self/oom_score_adj to 0

sshd[2198]: debug1: rexec start in 5 out 5 newsock 5 pipe 7 sock 8

sshd[2198]: debug1: inetd sockets after dupping: 3, 3

sshd[2198]: Connection from 192.168.1.6 port 47991

sshd[2198]: debug1: Client protocol version 2.0; client software version OpenSSH_6.1p1 Debian-4

sshd[2198]: debug1: match: OpenSSH_6.1p1 Debian-4 pat OpenSSH*

sshd[2198]: debug1: Enabling compatibility mode for protocol 2.0

sshd[2198]: debug1: Local version string SSH-2.0-OpenSSH_6.1p1 Debian-4

sshd[2198]: debug1: permanently_set_uid: 103/65534 [preauth]

sshd[2198]: debug1: list_hostkey_types: ssh-rsa,ssh-dss,ecdsa-sha2-nistp256 [preauth]

sshd[2198]: debug1: SSH2_MSG_KEXINIT sent [preauth]

sshd[2198]: debug1: SSH2_MSG_KEXINIT received [preauth]

sshd[2198]: debug1: kex: client->server aes128-ctr hmac-md5 none [preauth]

sshd[2198]: debug1: kex: server->client aes128-ctr hmac-md5 none [preauth]

sshd[2198]: debug1: expecting SSH2_MSG_KEX_ECDH_INIT [preauth]

sshd[2198]: debug1: SSH2_MSG_NEWKEYS sent [preauth]

sshd[2198]: debug1: expecting SSH2_MSG_NEWKEYS [preauth]

sshd[2198]: Connection closed by 192.168.1.6 [preauth]

sshd[2198]: debug1: do_cleanup [preauth]

sshd[2198]: debug1: monitor_read_log: child log fd closed

sshd[2198]: debug1: do_cleanup

sshd[2198]: debug1: Killing privsep child 2199

Does anyone have an idea what I am missing here?

UPDATE

The auth.log with debug level 3:

sshd[2455]: debug3: fd 5 is not O_NONBLOCK

sshd[2455]: debug1: Forked child 2456.

sshd[2455]: debug3: send_rexec_state: entering fd = 8 config len 751

sshd[2455]: debug3: ssh_msg_send: type 0

sshd[2455]: debug3: send_rexec_state: done

sshd[2456]: debug3: oom_adjust_restore

sshd[2456]: Set /proc/self/oom_score_adj to 0

sshd[2456]: debug1: rexec start in 5 out 5 newsock 5 pipe 7 sock 8

sshd[2456]: debug1: inetd sockets after dupping: 3, 3

sshd[2456]: Connection from 192.168.1.6 port 50037

sshd[2456]: debug1: Client protocol version 2.0; client software version OpenSSH_6.1p1 Debian-4

sshd[2456]: debug1: match: OpenSSH_6.1p1 Debian-4 pat OpenSSH*

sshd[2456]: debug1: Enabling compatibility mode for protocol 2.0

sshd[2456]: debug1: Local version string SSH-2.0-OpenSSH_6.1p1 Debian-4

sshd[2456]: debug2: fd 3 setting O_NONBLOCK

sshd[2456]: debug2: Network child is on pid 2457

sshd[2456]: debug3: preauth child monitor started

sshd[2456]: debug3: privsep user:group 103:65534 [preauth]

sshd[2456]: debug1: permanently_set_uid: 103/65534 [preauth]

sshd[2456]: debug1: list_hostkey_types: ssh-rsa,ssh-dss,ecdsa-sha2-nistp256 [preauth]

sshd[2456]: debug1: SSH2_MSG_KEXINIT sent [preauth]

sshd[2456]: debug1: SSH2_MSG_KEXINIT received [preauth]

sshd[2456]: 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 [preauth]

sshd[2456]: debug2: kex_parse_kexinit: ssh-rsa,ssh-dss,ecdsa-sha2-nistp256 [preauth]

sshd[2456]: debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se [preauth]

sshd[2456]: debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se [preauth]

sshd[2456]: debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96 [preauth]

sshd[2456]: debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96 [preauth]

sshd[2456]: debug2: kex_parse_kexinit: none,zlib@openssh.com [preauth]

sshd[2456]: debug2: kex_parse_kexinit: none,zlib@openssh.com [preauth]

sshd[2456]: debug2: kex_parse_kexinit:  [preauth]

sshd[2456]: debug2: kex_parse_kexinit:  [preauth]

sshd[2456]: debug2: kex_parse_kexinit: first_kex_follows 0  [preauth]

sshd[2456]: debug2: kex_parse_kexinit: reserved 0  [preauth]

sshd[2456]: 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 [preauth]

sshd[2456]: debug2: kex_parse_kexinit: ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,ssh-rsa,ssh-dss [preauth]

sshd[2456]: debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se [preauth]

sshd[2456]: debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se [preauth]

sshd[2456]: debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96 [preauth]

sshd[2456]: debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96 [preauth]

sshd[2456]: debug2: kex_parse_kexinit: none,zlib@openssh.com,zlib [preauth]

sshd[2456]: debug2: kex_parse_kexinit: none,zlib@openssh.com,zlib [preauth]

sshd[2456]: debug2: kex_parse_kexinit:  [preauth]

sshd[2456]: debug2: kex_parse_kexinit:  [preauth]

sshd[2456]: debug2: kex_parse_kexinit: first_kex_follows 0  [preauth]

sshd[2456]: debug2: kex_parse_kexinit: reserved 0  [preauth]

sshd[2456]: debug2: mac_setup: found hmac-md5 [preauth]

sshd[2456]: debug1: kex: client->server aes128-ctr hmac-md5 none [preauth]

sshd[2456]: debug2: mac_setup: found hmac-md5 [preauth]

sshd[2456]: debug1: kex: server->client aes128-ctr hmac-md5 none [preauth]

sshd[2456]: debug1: expecting SSH2_MSG_KEX_ECDH_INIT [preauth]

sshd[2456]: debug3: mm_key_sign entering [preauth]

sshd[2456]: debug3: mm_request_send entering: type 5 [preauth]

sshd[2456]: debug3: mm_key_sign: waiting for MONITOR_ANS_SIGN [preauth]

sshd[2456]: debug3: mm_request_receive_expect entering: type 6 [preauth]

sshd[2456]: debug3: mm_request_receive entering [preauth]

sshd[2456]: debug3: mm_request_receive entering

sshd[2456]: debug3: monitor_read: checking request 5

sshd[2456]: debug3: mm_answer_sign

sshd[2456]: debug3: mm_answer_sign: signature 0x7f9b687c7680(100)

sshd[2456]: debug3: mm_request_send entering: type 6

sshd[2456]: debug2: monitor_read: 5 used once, disabling now

sshd[2456]: debug2: kex_derive_keys [preauth]

sshd[2456]: debug2: set_newkeys: mode 1 [preauth]

sshd[2456]: debug1: SSH2_MSG_NEWKEYS sent [preauth]

sshd[2456]: debug1: expecting SSH2_MSG_NEWKEYS [preauth]

sshd[2456]: Connection closed by 192.168.1.6 [preauth]

sshd[2456]: debug1: do_cleanup [preauth]

sshd[2456]: debug3: PAM: sshpam_thread_cleanup entering [preauth]

sshd[2456]: debug1: monitor_read_log: child log fd closed

sshd[2456]: debug3: mm_request_receive entering

sshd[2456]: debug1: do_cleanup

sshd[2456]: debug3: PAM: sshpam_thread_cleanup entering

sshd[2456]: debug1: Killing privsep child 2457

UPDATE

I tried a manual sshfs mount and I also get read: Connection reset by peer. I then added the debuging options and also got Permission denied (publickey).. This is strange since the public key is in place and works fine otherwise. I also use my user for the ssh connection and manually specify the private key file. Could this be an issue with the root account not beeing able to access the correct public key on the server somewhere? I'm executing

sudo sshfs myuser@myserver:/mnt/foo /mnt/foo -o IdentityFile=/home/myuser/.ssh/id_rsa

and the relevant log part is

debug1: Authentications that can continue: publickey

debug1: Next authentication method: publickey

debug1: Offering RSA public key: /home/myuser/.ssh/id_rsa

debug1: Authentications that can continue: publickey

debug1: No more authentication methods to try.

Permission denied (publickey).

read: Connection reset by peer

The output looks exactly like one from a ssh session which refuses to connect due to server key fingerprint mismatch (or an unknown key). Does sftp to the server work correctly? – peterph  Oct 12 '13 at 8:19
	I tried sftp with both Nautilus (Connect to Server... option) and Filezilla. It works fine. Although Filezilla asked my about an unknown host key. – André Stannek  Oct 12 '13 at 11:09
	Try sftp directly - that is what SSHFS uses. – peterph  Oct 12 '13 at 15:23
2	Looks the same to me. Have you tried to get some debugging info from the client? sshfs -odebug,sshfs_debug,loglevel=debug ... could do the trick (taken from sourceforge.net/apps/mediawiki/fuse/index.php?title=SshfsFaq ‌​). – peterph  Oct 12 '13 at 16:54
1	@peterph already got that idea ;-) See my second update. I just omitted the debug parameters in the command posted here but I executed it with them. – André Stannek  Oct 12 '13 at 16:57

After a lot more of trying it turns out my client user wasn't in the fuse group. After I added it with sudo usermod -a -G fuse myuser the mount works fine again. Don't ask me how it could have worked before reinstalling the server. Thank for all your help!

I found my problem, which was similar, had to do with the fuse configuration file in:

/etc/fuse.conf

I had to un-comment:

user_allow_other