Centos 6.3上用OpenSSH实现无密码登录过程中出现问题的一般调试步骤

这次在Centos 6.3上实现无密码登录，发现怎么样都没能成功，无论怎样，还是需要密码，一下为解决方法
1. 查看ssh 登录的详细信息

ssh -v localhost

发现如下信息：

[shgong@localhost ~]$ ssh -v localhost
OpenSSH_5.3p1, OpenSSL 1.0.0-fips 29 Mar 2010
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to localhost [::1] port 22.
debug1: Connection established.
debug1: identity file /home/shgong/.ssh/identity type -1
debug1: identity file /home/shgong/.ssh/id_rsa type 1
debug1: identity file /home/shgong/.ssh/id_dsa type 2
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.3
debug1: match: OpenSSH_5.3 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.3
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host 'localhost' is known and matches the RSA host key.
debug1: Found key in /home/shgong/.ssh/known_hosts:1
debug1: ssh_rsa_verify: signature correct
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
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: gssapi-keyex
debug1: No valid Key exchange context
debug1: Next authentication method: gssapi-with-mic
debug1: Unspecified GSS failure.  Minor code may provide more information
Credentials cache file '/tmp/krb5cc_500' not found

debug1: Unspecified GSS failure.  Minor code may provide more information
Credentials cache file '/tmp/krb5cc_500' not found

debug1: Unspecified GSS failure.  Minor code may provide more information

debug1: Unspecified GSS failure.  Minor code may provide more information

debug1: Next authentication method: publickey
debug1: Trying private key: /home/shgong/.ssh/identity
debug1: Offering public key: /home/shgong/.ssh/id_rsa
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Offering public key: /home/shgong/.ssh/id_dsa
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: password

上面看出了整个登录过程

2. 用root查询系统登录日志

$tail /var/log/secure -n 20

发现如下日志信息：

Sep 15 21:40:06 localhost sudo:   shgong : TTY=pts/17 ; PWD=/home/shgong ; USER=root ; COMMAND=/sbin/service sshd restart
Sep 15 21:40:06 localhost sshd[4103]: Received signal 15; terminating.
Sep 15 21:40:06 localhost sshd[4228]: Server listening on 0.0.0.0 port 22.
Sep 15 21:40:06 localhost sshd[4228]: Server listening on :: port 22.
Sep 15 21:41:13 localhost sshd[4235]: Authentication refused: bad ownership or modes for file /home/shgong/.ssh/authorized_keys
Sep 15 21:41:13 localhost sshd[4235]: Authentication refused: bad ownership or modes for file /home/shgong/.ssh/authorized_keys
Sep 15 21:41:13 localhost sshd[4235]: Authentication refused: bad ownership or modes for file /home/shgong/.ssh/authorized_keys
Sep 15 21:41:13 localhost sshd[4235]: Authentication refused: bad ownership or modes for file /home/shgong/.ssh/authorized_keys

上面可以看出，无密码登录失败的原因在于authorized_keys的文件权限不对

[shgong@localhost ~]$ ls -lh ~/.ssh/
total 24K
-rw-------. 1 shgong shgong 1.5K Sep 15 21:41 authorized_keys
-rw-------. 1 shgong shgong  668 Sep 15 21:36 id_dsa
-rw-r--r--. 1 shgong shgong  618 Sep 15 21:36 id_dsa.pub
-rw-------. 1 shgong shgong 1.7K Sep 15 21:40 id_rsa
-rw-r--r--. 1 shgong shgong  410 Sep 15 21:40 id_rsa.pub
-rw-r--r--. 1 shgong shgong  391 Sep 15 21:36 known_hosts

3.修改文件权限

[shgong@localhost ~]$ chmod 600 ~/.ssh/authorized_keys

4.重新登录

[shgong@localhost ~]$ ssh -v localhost
OpenSSH_5.3p1, OpenSSL 1.0.0-fips 29 Mar 2010
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to localhost [::1] port 22.
debug1: Connection established.
debug1: identity file /home/shgong/.ssh/identity type -1
debug1: identity file /home/shgong/.ssh/id_rsa type 1
debug1: identity file /home/shgong/.ssh/id_dsa type 2
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.3
debug1: match: OpenSSH_5.3 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.3
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host 'localhost' is known and matches the RSA host key.
debug1: Found key in /home/shgong/.ssh/known_hosts:1
debug1: ssh_rsa_verify: signature correct
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
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: gssapi-keyex
debug1: No valid Key exchange context
debug1: Next authentication method: gssapi-with-mic
debug1: Unspecified GSS failure.  Minor code may provide more information
Credentials cache file '/tmp/krb5cc_500' not found

debug1: Unspecified GSS failure.  Minor code may provide more information
Credentials cache file '/tmp/krb5cc_500' not found

debug1: Unspecified GSS failure.  Minor code may provide more information

debug1: Unspecified GSS failure.  Minor code may provide more information

debug1: Next authentication method: publickey
debug1: Trying private key: /home/shgong/.ssh/identity
debug1: Offering public key: /home/shgong/.ssh/id_rsa
debug1: Server accepts key: pkalg ssh-rsa blen 277
debug1: read PEM private key done: type RSA
debug1: Authentication succeeded (publickey).
debug1: channel 0: new [client-session]
debug1: Requesting no-more-sessions@openssh.com
debug1: Entering interactive session.
debug1: Sending environment.
debug1: Sending env XMODIFIERS = @im=ibus
debug1: Sending env LANG = en_US.UTF-8

登录成功！