[Linux] SSH 연결 실패 시 debug 방법

[Linux] SSH 연결 실패 시 debug 방법

ssh 연결 과정 debug 분석

• ssh -v / ssh -vv / ssh -vvv 명령어로 확인
• 공개키파일 경로 확인 및 인증 과정을 확인할 수 있음

[root@clu_1 ssh]# ssh localhost -v
OpenSSH_6.6.1, OpenSSL 1.0.1e-fips 11 Feb 2013
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 56: Applying options for *
debug1: Connecting to localhost [::1] port 22.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: identity file /root/.ssh/id_rsa type 1
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: identity file /root/.ssh/id_dsa type -1
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: identity file /root/.ssh/id_ecdsa type -1
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: identity file /root/.ssh/id_ed25519 type -1
debug1: identity file /root/.ssh/id_ed25519-cert type -1

PasswordAuthentication 설정을 no 로 설정 시 ssh 접속 실패 debug

• sshd_config 설정 [root@server1 ~]# cat /etc/ssh/sshd_config | grep PasswordAuthentication PasswordAuthentication no
• Authentications 방식이 publickey,gssapi-keyex,gssapi-with-mic으로 제한되어 있어 Permission denied 발생

Chois-MacBook-Pro:~ user$ ssh root@192.168.56.6 -v
OpenSSH_7.7p1, LibreSSL 2.7.3
... 중략 ... 
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic
debug1: Next authentication method: publickey
debug1: Trying private key: /Users/userkey: /Users/user/.ssh/id_dsa
debug1: Trying private key: /Users/user/.ssh/id_ecdsa
debug1: Trying private key: /Users/user/.ssh/id_ed25519
debug1: Trying private key: /Users/user/.ssh/id_xmss
debug1: No more authentication methods to try.
root@192.168.56.6: Permission denied (publickey,gssapi-keyex,gssapi-with-mic).
​

• sshd_config 설정에서 PasswordAuthentication을 yes로 변경 시 [root@server1 ~]# cat /etc/ssh/sshd_config | grep PasswordAuthentication PasswordAuthentication no

• Authentications 방식이 publickey,gssapi-keyex,gssapi-with-mic,password 으로 password 가 추가 됨

  • Authentications 순서는 publickey -> password 순이다.

Chois-MacBook-Pro:.ssh user$ ssh root@192.168.56.6 -v
OpenSSH_7.7p1, LibreSSL 2.7.3
... 중략 ... 
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: publickey
debug1: Trying private key: /Users/user/.ssh/id_rsa
debug1: Trying private key: /Users/user/.ssh/id_dsa
debug1: Trying private key: /Users/user/.ssh/id_ecdsa
debug1: Trying private key: /Users/user/.ssh/id_ed25519
debug1: Trying private key: /Users/user/.ssh/id_xmss
debug1: Next authentication method: password
root@192.168.56.6's password:
debug1: Authentication succeeded (password).
Authenticated to 192.168.56.6 ([192.168.56.6]:22).
debug1: channel 0: new [client-session]
debug1: Requesting no-more-sessions@openssh.com
... 
[root@clu_1 ~]#