Почему я должен установить usePAM на 'нет' для управления соединением SSH?

У меня есть названный user1 пользователя системы (основной). Я попытался установить соединение SSH между названным foreignuser пользователя и основным (user1). Для этого я генерировал несколько ключей с ssh-keygen. Я добавил открытый ключ foreignuser в .ssh/authorized_keys файл пользователя user1. Я проверил полномочия .ssh папки (700) и .ssh/authorized_keys файл (600). Все в порядке. Я могу соединиться как user1 от foreignuser.

Теперь, я добавил, что новый пользователь назвал user2 (я использую Kubuntu). Я повторил точно те же шаги. Но на этот раз, когда я пытаюсь соединиться как user2 от foreignuser, я получаю это:

Connection closed by 192.168.0.201

Но, если я перехожу к файлу /etc/ssh/sshd_config и переключите строку usePAM yes кому: usePAM no, сохраните и перезапуск ssh сервис, я могу соединиться как user2 от foreignuser.

Что могло происходить? Если usePAM установлен на yes и я пытаюсь соединиться через ssh с -vvv, Я получаю следующее:

OpenSSH_6.2p2 Ubuntu-6ubuntu0.4, OpenSSL 1.0.1e 11 Feb 2013                                                                          
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 192.168.0.201 [192.168.0.201] port 8022.
debug1: Connection established.
debug3: Incorrect RSA1 identifier
debug3: Could not load "/home/foreignuser/.ssh/id_rsa" as a RSA1 public key
debug1: identity file /home/foreignuser/.ssh/id_rsa type 1
debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-4096
debug1: Checking blacklist file /etc/ssh/blacklist.RSA-4096
debug1: identity file /home/foreignuser/.ssh/id_rsa-cert type -1
debug1: identity file /home/foreignuser/.ssh/id_dsa type -1
debug1: identity file /home/foreignuser/.ssh/id_dsa-cert type -1
debug1: identity file /home/foreignuser/.ssh/id_ecdsa type -1
debug1: identity file /home/foreignuser/.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-6ubuntu0.4
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.2p2 Ubuntu-6ubuntu0.4
debug1: match: OpenSSH_6.2p2 Ubuntu-6ubuntu0.4 pat OpenSSH*
debug2: fd 3 setting O_NONBLOCK
debug3: put_host_port: [192.168.0.201]:8022
debug3: load_hostkeys: loading entries for host "[192.168.0.201]:8022" from file "/home/foreignuser/.ssh/known_hosts"
debug3: load_hostkeys: found key type ECDSA in file /home/foreignuser/.ssh/known_hosts:31
debug3: load_hostkeys: loaded 1 keys
debug3: order_hostkeyalgs: prefer hostkeyalgs: 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
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: 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
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,zlib
debug2: kex_parse_kexinit: none,zlib@openssh.com,zlib
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,ecdsa-sha2-nistp256
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 none
debug2: mac_setup: found hmac-md5-etm@openssh.com
debug1: kex: client->server aes128-ctr hmac-md5-etm@openssh.com none
debug1: sending SSH2_MSG_KEX_ECDH_INIT
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ECDSA 80:e4:73:c4:4d:a9:30:97:08:3c:f9:f8:ab:80:f4:72
debug3: put_host_port: [192.168.0.201]:8022
debug3: put_host_port: [192.168.0.201]:8022
debug3: load_hostkeys: loading entries for host "[192.168.0.201]:8022" from file "/home/foreignuser/.ssh/known_hosts"
debug3: load_hostkeys: found key type ECDSA in file /home/foreignuser/.ssh/known_hosts:31
debug3: load_hostkeys: loaded 1 keys
debug3: load_hostkeys: loading entries for host "[192.168.0.201]:8022" from file "/home/foreignuser/.ssh/known_hosts"
debug3: load_hostkeys: found key type ECDSA in file /home/foreignuser/.ssh/known_hosts:31
debug3: load_hostkeys: loaded 1 keys
debug1: Host '[192.168.0.201]:8022' is known and matches the ECDSA host key.
debug1: Found key in /home/foreignuser/.ssh/known_hosts:31
debug1: ssh_ecdsa_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/foreignuser/.ssh/id_rsa (0x7fc896efb2a0),
debug2: key: /home/foreignuser/.ssh/id_dsa ((nil)),
debug2: key: /home/foreignuser/.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/foreignuser/.ssh/id_rsa
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Server accepts key: pkalg ssh-rsa blen 535
debug2: input_userauth_pk_ok: fp 8d:1e:b2:59:64:e5:07:bf:5c:9e:5b:ad:45:8a:c8:c2
debug3: sign_and_send_pubkey: RSA 8d:1e:b2:59:64:e5:07:bf:5c:9e:5b:ad:45:8a:c8:c2
debug1: read PEM private key done: type RSA
Connection closed by 192.168.0.201