在我的 Ubuntu 15.10 上，甚至无法与本地主机建立简单的 SSH 连接。服务器是在几个月前设置的，能够使用密钥创建 SSH 访问权限，但无法为新用户复制该远程访问权限。我可以从原始用户使用 PuTTY 进行访问，但即使该用户也无法通过本地主机进行访问。
为了解决问题，我尝试简单地通过本地主机和裸密码进行访问，希望尽量减少可能出错的变量 - 如果有更好的测试，请告诉我。
我有 fail2ban 和防火墙，但由于我可以使用原始帐户远程访问服务器，因此我不会立即怀疑这些是问题所在。不过，防火墙规则输出如下。
以下是我遵循的步骤和更多数据：
创建新用户并设置密码
sudo useradd teachers -m -s /bin/bash;
sudo passwd teachers;
配置 SSH（/etc/ssh/sshd_config）进行基本访问测试
AllowUsers teachers
PasswordAuthentication yes
LogLevel VERBOSE
此时还没有 SSH 密钥，因为我只是想获取密码访问权限。
这是我在命令行尝试的输出：
~$ ssh -v localhost
OpenSSH_6.9p1 Ubuntu-2ubuntu0.1, OpenSSL 1.0.2d 9 Jul 2015
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to localhost [127.0.0.1] port 22.
debug1: Connection established.
debug1: SELinux support disabled
debug1: key_load_public: No such file or directory
debug1: identity file /home/teachers/.ssh/id_rsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/teachers/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/teachers/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/teachers/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/teachers/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/teachers/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/teachers/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/teachers/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.9p1 Ubuntu-2ubuntu0.1
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.9p1 Ubuntu-2ubuntu0.1
debug1: match: OpenSSH_6.9p1 Ubuntu-2ubuntu0.1 pat OpenSSH* compat 0x04000000
debug1: Authenticating to localhost:22 as 'teachers'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client [email protected] <implicit> none
debug1: kex: client->server [email protected] <implicit> none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:AS0MYlPqe9JOcx5ygQN9jIN2jdDV850oCSCmtp+cy2w
The authenticity of host 'localhost (127.0.0.1)' can't be established.
ECDSA key fingerprint is SHA256:AS0MYlPqe9JOcx5ygQN9jIN2jdDV850oCSCmtp+cy2w.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'localhost' (ECDSA) to the list of known hosts.
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
################################################################################
# This is a restricted system.... #
################################################################################
debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Trying private key: /home/teachers/.ssh/id_rsa
debug1: Trying private key: /home/teachers/.ssh/id_dsa
debug1: Trying private key: /home/teachers/.ssh/id_ecdsa
debug1: Trying private key: /home/teachers/.ssh/id_ed25519
debug1: Next authentication method: password
teachers@localhost's password:
debug1: Authentications that can continue: publickey,password
Permission denied, please try again.
teachers@localhost's password:
debug1: Authentications that can continue: publickey,password
Permission denied, please try again.
teachers@localhost's password:
debug1: Authentications that can continue: publickey,password
debug1: No more authentication methods to try.
Permission denied (publickey,password).
这是我尝试访问时的 auth.log：
Apr 19 05:41:52 lists sshd[27165]: Set /proc/self/oom_score_adj to 0
Apr 19 05:41:52 lists sshd[27165]: Connection from 127.0.0.1 port 45192 on 127.0.0.1 port 22
Apr 19 05:42:03 lists sshd[27165]: PAM (sshd) illegal module type: umask
Apr 19 05:42:03 lists sshd[27165]: PAM pam_parse: expecting return value; [...002]
Apr 19 05:42:03 lists sshd[27165]: PAM (sshd) no module name supplied
Apr 19 05:42:13 lists sshd[27165]: Failed password for teachers from 127.0.0.1 port 45192 ssh2
Apr 19 05:42:20 lists sshd[27165]: Failed password for teachers from 127.0.0.1 port 45192 ssh2
Apr 19 05:42:27 lists sshd[27165]: Failed password for teachers from 127.0.0.1 port 45192 ssh2
Apr 19 05:42:27 lists sshd[27165]: Connection closed by 127.0.0.1 [preauth]
以下是我的 iptables 的输出：
$ sudo iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
DROP tcp -- 222.0.0.0/8 anywhere tcp dpt:ssh
fail2ban-dovecot tcp -- anywhere anywhere multiport dports smtp,urd,submission,imap2,imap3,imaps,pop3,pop3s
fail2ban-postfix tcp -- anywhere anywhere multiport dports smtp,urd,submission
fail2ban-sasl tcp -- anywhere anywhere multiport dports smtp,urd,submission,imap2,imap3,imaps,pop3,pop3s
fail2ban-ssh tcp -- anywhere anywhere multiport dports ssh
DROP tcp -- 222.186.34.202 anywhere tcp dpt:ssh
fail2ban-dovecot tcp -- anywhere anywhere multiport dports smtp,urd,submission,imap2,imap3,imaps,pop3,pop3s
fail2ban-postfix tcp -- anywhere anywhere multiport dports smtp,urd,submission
fail2ban-sasl tcp -- anywhere anywhere multiport dports smtp,urd,submission,imap2,imap3,imaps,pop3,pop3s
fail2ban-ssh tcp -- anywhere anywhere multiport dports ssh
ACCEPT all -- anywhere anywhere
ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED
ACCEPT tcp -- anywhere anywhere tcp dpt:ssh
ACCEPT tcp -- anywhere anywhere tcp dpt:http
LOG all -- anywhere anywhere limit: avg 5/min burst 5 LOG level debug prefix "iptables denied: "
ACCEPT tcp -- anywhere anywhere tcp dpt:https
ACCEPT tcp -- anywhere anywhere tcp dpt:2812
ACCEPT tcp -- anywhere anywhere tcp dpt:smtp
ACCEPT tcp -- anywhere anywhere tcp dpt:pop3
ACCEPT tcp -- anywhere anywhere tcp dpt:submission
DROP all -- anywhere anywhere
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
Chain fail2ban-dovecot (2 references)
target prot opt source destination
RETURN all -- anywhere anywhere
RETURN all -- anywhere anywhere
Chain fail2ban-postfix (2 references)
target prot opt source destination
RETURN all -- anywhere anywhere
RETURN all -- anywhere anywhere
Chain fail2ban-sasl (2 references)
target prot opt source destination
RETURN all -- anywhere anywhere
RETURN all -- anywhere anywhere
Chain fail2ban-ssh (2 references)
target prot opt source destination
RETURN all -- anywhere anywhere
RETURN all -- anywhere anywhere
我相信这表明端口 22 应该可用：
$ nc -z -v -w 5 localhost 22
Connection to localhost 22 port [tcp/ssh] succeeded!
编辑：包括 sshd 配置：
$ cat /etc/ssh/sshd_config
# What ports, IPs and protocols we listen for
Port 22
# Use these options to restrict which interfaces/protocols sshd will bind to
#ListenAddress ::
#ListenAddress 0.0.0.0
Protocol 2
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes
# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 1024
# Logging
SyslogFacility AUTH
LogLevel VERBOSE
# Authentication:
LoginGraceTime 120
PermitRootLogin no
StrictModes yes
RSAAuthentication yes
PubkeyAuthentication yes
#AuthorizedKeysFile %h/.ssh/authorized_keys
# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
#IgnoreUserKnownHosts yes
# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no
# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no
# Change to no to disable tunnelled clear text passwords
PasswordAuthentication yes
# Kerberos options
#KerberosAuthentication no
#KerberosGetAFSToken no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes
# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes
X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no
#MaxStartups 10:30:60
Banner /etc/issue.net
# Allow client to pass locale environment variables
AcceptEnv LANG LC_*
Subsystem sftp /usr/lib/openssh/sftp-server
# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication. Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin yes
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
UsePAM yes
AllowUsers listman teachers
/etc/pam.d/ 中唯一的文件是 /etc/pam.d/sshd：
$ cat /etc/pam.d/sshd
# PAM configuration for the Secure Shell service
umask 002
# Standard Un*x authentication.
@include common-auth
# Disallow non-root logins when /etc/nologin exists.
account required pam_nologin.so
# Uncomment and edit /etc/security/access.conf if you need to set complex
# access limits that are hard to express in sshd_config.
# account required pam_access.so
# Standard Un*x authorization.
@include common-account
# SELinux needs to be the first session rule. This ensures that any
# lingering context has been cleared. Without this it is possible that a
# module could execute code in the wrong domain.
session [success=ok ignore=ignore module_unknown=ignore default=bad] pam_selinux.so close
# Set the loginuid process attribute.
session required pam_loginuid.so
# Create a new session keyring.
session optional pam_keyinit.so force revoke
# Standard Un*x session setup and teardown.
@include common-session
# Print the message of the day upon successful login.
# This includes a dynamically generated part from /run/motd.dynamic
# and a static (admin-editable) part from /etc/motd.
session optional pam_motd.so motd=/run/motd.dynamic
session optional pam_motd.so noupdate
# Print the status of the user's mailbox upon successful login.
session optional pam_mail.so standard noenv # [1]
# Set up user limits from /etc/security/limits.conf.
session required pam_limits.so
# Read environment variables from /etc/environment and
# /etc/security/pam_env.conf.
session required pam_env.so # [1]
# In Debian 4.0 (etch), locale-related environment variables were moved to
# /etc/default/locale, so read that as well.
session required pam_env.so user_readenv=1 envfile=/etc/default/locale
# SELinux needs to intervene at login time to ensure that the process starts
# in the proper default security context. Only sessions which are intended
# to run in the user's context should be run after this.
session [success=ok ignore=ignore module_unknown=ignore default=bad] pam_selinux.so open
# Standard Un*x password updating.
@include common-password
我在这里遗漏了什么？