如何启用 SSH 调试模式来排除 SSH 连接故障
在本文中，我们将向您展示如何在 Linux 中运行 SSH 时打开调试模式。这将使您能够看到当您使用详细模式或调试模式执行 ssh 命令连接到远程 Linux 服务器时实际发生的情况。
ssh 客户端的 -v 开关允许您在详细模式下运行 ssh，该模式会打印有关 SSH 连接进度的调试信息，这对于调试连接、身份验证和任何配置问题非常有用。
有不同程度的冗长；使用多个 -v 标志会增加详细程度（最大详细程度为 3）。
ssh -v– 会告诉您主要发生了什么。ssh -vv– 将通知您两端的级别都较低。ssh -vvv– 将通知您两端的所有信息。
以下命令将以第一详细级别运行 SSH，这为我们提供了大量调试信息，如图所示。
aaronkilik@tecmint ~ $ ssh -v [email
样本输出
OpenSSH_7.2p2 Ubuntu-4ubuntu2.2, OpenSSL 1.0.2g-fips 1 Mar 2016
debug1: Reading configuration data /home/aaronkilik/.ssh/config
debug1: /home/aaronkilik/.ssh/config line 18: Applying options for *
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to 192.168.56.10 [192.168.56.10] port 22.
debug1: Connection established.
debug1: identity file /home/aaronkilik/.ssh/id_rsa type 1
debug1: key_load_public: No such file or directory
debug1: identity file /home/aaronkilik/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/aaronkilik/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/aaronkilik/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/aaronkilik/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/aaronkilik/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/aaronkilik/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/aaronkilik/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.2p2 Ubuntu-4ubuntu2.2
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.4
debug1: match: OpenSSH_7.4 pat OpenSSH* compat 0x04000000
debug1: Authenticating to 192.168.56.10:22 as 'tecmint'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: [email
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: [email MAC:
compression: [email
debug1: kex: client->server cipher: [email MAC:
compression: [email
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256
SHA256:1778erqyug4tHJa7D6y/Ep4UWsUtNEOBSMaj32k9oO8
debug1: Host '192.168.56.10' is known and matches the ECDSA host key.
debug1: Found key in /home/aaronkilik/.ssh/known_hosts:8
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue:
publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /home/aaronkilik/.ssh/id_rsa
debug1: Server accepts key: pkalg rsa-sha2-512 blen 279
debug1: Enabling compression at level 6.
debug1: Authentication succeeded (publickey).
Authenticated to 192.168.56.10 ([192.168.56.10]:22).
debug1: channel 0: new [client-session]
debug1: Requesting [email
debug1: Entering interactive session.
debug1: pledge: network
debug1: client_input_global_request: rtype [email
want_reply 0
debug1: Sending environment.
debug1: Sending env LC_PAPER = lg_UG.UTF-8
debug1: Sending env LC_ADDRESS = lg_UG.UTF-8
debug1: Sending env LC_MONETARY = lg_UG.UTF-8
debug1: Sending env LC_NUMERIC = lg_UG.UTF-8
debug1: Sending env LC_TELEPHONE = lg_UG.UTF-8
debug1: Sending env LC_IDENTIFICATION = lg_UG.UTF-8
debug1: Sending env LANG = en_US.UTF-8
debug1: Sending env LC_MEASUREMENT = lg_UG.UTF-8
debug1: Sending env LC_NAME = lg_UG.UTF-8
Last login: Sat Jan 6 16:20:11 2018 from 192.168.56.1
当尝试注销或退出会话时，您还将看到如图所示的调试消息。
[tecmint@tecmint ~]$ exit
logout
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: client_input_channel_req: channel 0 rtype [email reply 0
debug1: channel 0: free: client-session, nchannels 1
Connection to 192.168.56.10 closed.
Transferred: sent 3392, received 3120 bytes, in 118.1 seconds
Bytes per second: sent 28.7, received 26.4
debug1: Exit status 0
debug1: compress outgoing: raw data 1159, compressed 573, factor 0.49
debug1: compress incoming: raw data 573, compressed 1159, factor 2.02
接下来，您可以为更多调试消息启用额外的（2 级和 3 级）详细程度，如图所示。
ssh -vv [email
ssh -vvv [email
就是这样！有关SSH的更多使用，请阅读以下相关文章。
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- 如何在 Linux 中设置 SSH 无密码登录
- 如何在 Linux 中断开不活动或空闲的 SSH 连接
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