ssh 开启debug
传统的ssh 使用方法：
ssh root@example.com
加上 -v之后就可以开启 debug模式， 可以看到详细的连接过程
ssh -v root@example.com
OpenSSH_7.4p1, OpenSSL 1.0.2k-fips 26 Jan 2017
debug1: Reading configuration data /home/root/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 56: Applying options for *
debug1: Connecting to seroiuvd02674.sero.gic.ericsson.se [192.168.1.2] port 22.
debug1: Connection established.
debug1: identity file /home/root/.ssh/id_rsa type 1
debug1: key_load_public: No such file or directory
debug1: identity file /home/root/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/root/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/root/.ssh/id_dsa-cert type -1
debug1: identity file /home/root/.ssh/id_ecdsa type 3
debug1: key_load_public: No such file or directory
debug1: identity file /home/root/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/root/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/root/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.4
debug1: Remote protocol version 2.0, remote software version OpenSSH_8.0
debug1: match: OpenSSH_8.0 pat OpenSSH* compat 0x04000000
debug1: Authenticating to example.com:22 as 'root'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: kex: curve25519-sha256 need=64 dh_need=64
debug1: kex: curve25519-sha256 need=64 dh_need=64
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:BXJcbrSOLohgyh8cA2aERBdEf3YCD8b5lUQdcK9ypYg
debug1: Host 'example.com' is known and matches the ECDSA host key.
debug1: Found key in /home/root/.ssh/known_hosts:3934
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521>
debug1: SSH2_MSG_SERVICE_ACCEPT received
These computer resources, specifically Internet access and E-mail, are
provided for authorized users only. For legal, security and cost
reasons, utilization and access of resources are monitored and recorded
in log files. All information (whether business or personal) that is
created, received, downloaded, stored, sent or otherwise processed can
be accessed, reviewed, copied, recorded or deleted by Ericsson, in
accordance with approved internal procedures, at any time if deemed
necessary or appropriate, and without advance notice. Any evidence of
unauthorized access or misuse of Ericsson resources may result in
disciplinary actions, including termination of employment or assignment,
and could subject a user to criminal prosecution. Your use of Ericsson's
computer resources constitutes your consent to Ericsson's Policies and
Directives, including the provisions stated above.
IF YOU ARE NOT AN AUTHORIZED USER, PLEASE EXIT IMMEDIATELY
You are connected to: example.com
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password,keyboard-interactive
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
No Kerberos credentials available (default cache: KEYRING:persistent:319721)
debug1: Unspecified GSS failure. Minor code may provide more information
No Kerberos credentials available (default cache: KEYRING:persistent:319721)
debug1: Next authentication method: publickey
```sh
开启debug 模式之后， 很清晰的能看到两个重要信息，
debug1: Reading configuration data /home/root/.ssh/config 从家目录下读取配置信息
debug1: Reading configuration data /etc/ssh/ssh_config 从根目录的ssh里面读取信息
