无法通过SSH连接AWS Ubuntu实例的问题求助

问题描述 #

AWS Ubuntu实例此前SSH连接正常，今日登录时持续被拒。已尝试将PEM文件权限设为chmod 400和chmod 600，以root用户连接时收到提示：

Please login as the user "ubuntu" rather than the user "root".
使用sudo执行SSH命令仍无法连接，ssh -vvv -i {pemfile} ubuntu@{ip}的调试输出如下：

ssh -vvv -i "myfile.pem" ubuntu@ec2-xx-xxx-xxx-xxx.ap-xxxx-1.compute.amazonaws.com
OpenSSH_8.2p1 Ubuntu-4ubuntu0.5, OpenSSL 1.1.1f  31 Mar 2020
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: include /etc/ssh/ssh_config.d/*.conf matched no files
debug1: /etc/ssh/ssh_config line 21: Applying options for *
debug2: resolving "ec2-xx-xxx-xxx-xxx.ap-xxxx-1.compute.amazonaws.com" port 22
debug2: ssh_connect_direct
debug1: Connecting to ec2-xx-xxx-xxx-xxx.ap-xxxx-1.compute.amazonaws.com [13.xxx.xxx.xxx] port 22.
debug1: Connection established.
debug1: identity file myfile.pem type -1
debug1: identity file myfile.pem-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.2p1 Ubuntu-4ubuntu0.5
debug1: Remote protocol version 2.0, remote software version OpenSSH_8.9p1 Ubuntu-3
debug1: match: OpenSSH_8.9p1 Ubuntu-3 pat OpenSSH* compat 0x04000000
debug2: fd 3 setting O_NONBLOCK
debug1: Authenticating to ec2-xx-xxx-xxx-xxx.ap-xxxx-1.compute.amazonaws.com:22 as 'ubuntu'
debug3: hostkeys_foreach: reading file "/home/user/.ssh/known_hosts"
debug3: record_hostkey: found key type ECDSA in file /home/user/.ssh/known_hosts:40
debug3: load_hostkeys: loaded 1 keys from ec2-xx-xxx-xxx-xxx.ap-xxxx-1.compute.amazonaws.com
debug3: order_hostkeyalgs: prefer hostkeyalgs: ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521
debug3: send packet: type 20
debug1: SSH2_MSG_KEXINIT sent
debug3: receive packet: type 20
debug1: SSH2_MSG_KEXINIT received
debug2: local client KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,ext-info-c
debug2: host key algorithms: ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,ssh-ed25519-cert-v01@openssh.com,sk-ssh-ed25519-cert-v01@openssh.com,rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,sk-ecdsa-sha2-nistp256@openssh.com,ssh-ed25519,sk-ssh-ed25519@openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa
debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,zlib@openssh.com,zlib
debug2: compression stoc: none,zlib@openssh.com,zlib
debug2: languages ctos: 
debug2: languages stoc: 
debug2: first_kex_follows 0 
debug2: reserved 0 
debug2: peer server KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,sntrup761x25519-sha512@openssh.com,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256
debug2: host key algorithms: rsa-sha2-512,rsa-sha2-256,ecdsa-sha2-nistp256,ssh-ed25519
debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,zlib@openssh.com
debug2: compression stoc: none,zlib@openssh.com
debug2: languages ctos: 
debug2: languages stoc: 
debug2: first_kex_follows 0 
debug2: reserved 0 
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
debug3: send packet: type 30
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug3: receive packet: type 31
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:kaOCGj+Dgbbm8LqMeci7YjRjl5zBYHDhgq173rGs9ZA
debug3: hostkeys_foreach: reading file "/home/user/.ssh/known_hosts"
debug3: record_hostkey: found key type ECDSA in file /home/user/.ssh/known_hosts:40
debug3: load_hostkeys: loaded 1 keys from ec2-xx-xxx-xxx-xxx.ap-xxxx-1.compute.amazonaws.com
debug3: hostkeys_foreach: reading file "/home/user/.ssh/known_hosts"
debug3: record_hostkey: found key type ECDSA in file /home/user/.ssh/known_hosts:41
debug3: load_hostkeys: loaded 1 keys from 13.xxx.xxx.xxx
debug1: Host 'ec2-xx-xxx-xxx-xxx.ap-xxxx-1.compute.amazonaws.com' is known and matches the ECDSA host key.
debug1: Found key in /home/user/.ssh/known_hosts:40
debug3: send packet: type 21
debug2: set_newkeys: mode 1
debug1: rekey out after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug3: receive packet: type 21
debug1: SSH2_MSG_NEWKEYS received
debug2: set_newkeys: mode 0
debug1: rekey in after 134217728 blocks
debug1: Will attempt key: myfile.pem RSA SHA256:hQqliBUwEKzZ+ZCA/K9hIoODTG+Ao9IsDNp/ncSl7CM agent
debug1: Will attempt key: myfile.pem  explicit
debug2: pubkey_prepare: done
debug3: send packet: type 5
debug3: receive packet: type 7
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,sk-ssh-ed25519@openssh.com,ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,sk-ecdsa-sha2-nistp256@openssh.com,webauthn-sk-ecdsa-sha2-nistp256@openssh.com>
debug1: kex_input_ext_info: publickey-hostbound@openssh.com (unrecognised)
debug3: receive packet: type 6
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug3: send packet: type 50
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey
debug3: start over, passed a different list publickey
debug3: preferred gssapi-with-mic,publickey,keyboard-interactive,password
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Offering public key: myfile.pem RSA SHA256:hQqliBUwEKzZ+ZCA/K9hIoODTG+Ao9IsDNp/ncSl7CM agent
debug3: send packet: type 50
debug2: we sent a publickey packet, wait for reply
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey
debug1: Trying private key: myfile.pem
debug3: sign_and_send_pubkey: RSA SHA256:hQqliBUwEKzZ+ZCA/K9hIoODTG+Ao9IsDNp/ncSl7CM
debug3: sign_and_send_pubkey: signing using rsa-sha2-512 SHA256:hQqliBUwEKzZ+ZCA/K9hIoODTG+Ao9IsDNp/ncSl7CM
debug3: send packet: type 50
debug2: we sent a publickey packet, wait for reply
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey
debug2: we did not send a packet, disable method
debug1: No more authentication methods to try.
ubuntu@ec2-xx-xxx-xxx-xxx.ap-xxxx-1.compute.amazonaws.com: Permission denied (publickey).

排查与解决步骤 #

从日志可见，TCP连接已建立，但公钥认证始终失败，按以下顺序排查：

1. 确认PEM文件有效性

   • 核实是否使用实例创建时下载的对应PEM文件，若文件丢失或损坏，替换为正确密钥文件。
   • 严格设置文件权限为chmod 400 myfile.pem，避免权限过宽导致SSH拒绝使用该密钥。

2. 检查实例端公钥配置

   • 通过AWS控制台的EC2 Instance Connect临时登录实例（需安全组允许对应入站流量）。
   • 登录后执行以下操作：
     • 生成本地PEM文件的公钥：ssh-keygen -y -f myfile.pem，对比/home/ubuntu/.ssh/authorized_keys中的内容，确保公钥完全一致。
     • 修复权限：

       chmod 700 /home/ubuntu/.ssh
       chmod 600 /home/ubuntu/.ssh/authorized_keys
       chown ubuntu:ubuntu /home/ubuntu/.ssh -R
       

3. 验证SSH服务配置

   • 查看/etc/ssh/sshd_config，确保：
     • PubkeyAuthentication yes
     • 若需临时测试，可将PasswordAuthentication no改为yes，登录成功后改回。
   • 重启SSH服务：sudo systemctl restart sshd

4. 检查网络与安全组

   • 确认实例安全组允许本地IP访问22端口。
   • 核实实例公网IP或域名未变更，确保连接地址正确。

5. 清除本地旧密钥记录

   • 若实例曾更换密钥或重建，执行ssh-keygen -R ec2-xx-xxx-xxx-xxx.ap-xxxx-1.compute.amazonaws.com清除本地known_hosts中的旧记录后重试。

内容的提问来源于stack exchange，提问作者HIMAL B