解鎖 AWS 託管的 Ubuntu 伺服器使用者帳戶，只能訪問文件系統

我使用其中一個 Ubuntu Server AMI 啟動了一個 AWS 實例，使用預設使用者 (ubuntu) 和密鑰文件成功登錄，安裝了一些東西，添加了一些使用者，斷開連接並忘記了幾個星期。

今天我發現我不能再 ssh 到它了，使用第一次沒問題的相同憑據：

$ ssh -i ~/path/key.pem ubuntu@1.2.3.4
Connection closed by 1.2.3.4 port 22

$ ssh -v -i ~/path/key.pem ubuntu@1.2.3.4
OpenSSH_7.6p1 Ubuntu-4ubuntu0.3, OpenSSL 1.0.2n  7 Dec 2017
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to 1.2.3.4 [1.2.3.4] port 22.
debug1: Connection established.
debug1: key_load_public: No such file or directory
debug1: identity file /path/key.pem type -1
debug1: key_load_public: No such file or directory
debug1: identity file /path/key.pem-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_7.6p1 Ubuntu-4ubuntu0.3
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.6p1 Ubuntu-4ubuntu0.3
debug1: match: OpenSSH_7.6p1 Ubuntu-4ubuntu0.3 pat OpenSSH* compat 0x04000000
debug1: Authenticating to 1.2.3.4:22 as 'ubuntu'
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: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:a/4u6R0qGP4SviSke0OWOOIaSjqymNvexBZDJ+yoOXc
debug1: Host '1.2.3.4' is known and matches the ECDSA host key.
debug1: Found key in /home/user/.ssh/known_hosts:45
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
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Offering public key: RSA SHA256:nd8gr8BrgC88h1hobmvdNMHOWNmWukYc4L0SJswVolk user@host
debug1: Authentications that can continue: publickey
debug1: Trying private key: /path/key.pem
Connection closed by 1.2.3.4 port 22

所以我停止了實例，分離了卷，並將捲附加到我能夠登錄的實例上。這允許我掛載卷、訪問文件並研究 ssh 配置和日誌。

這就是我發現使用者帳戶由於某種原因被鎖定的方式：

$ cd /path/to/mounted/volume
$ tail var/log/auth.log
Mar 15 13:10:24 sshd[1145]: Server listening on 0.0.0.0 port 22.
Mar 15 13:10:24 sshd[1145]: Server listening on :: port 22.
Mar 15 13:14:09 sshd[1430]: User ubuntu not allowed because account is locked
Mar 15 13:17:01 CRON[1440]: pam_unix(cron:session): session opened for user root by (uid=0)
Mar 15 13:17:01 CRON[1440]: pam_unix(cron:session): session closed for user root
Mar 15 13:26:07 sshd[1473]: User another_user not allowed because account is locked
Mar 15 13:26:07 sshd[1473]: Connection closed by invalid user another_user 212.93.116.117 port 36868 [preauth]
Mar 15 13:27:42 sshd[1475]: Bad protocol version identification '\377\364\377\375\006\033\033' from 212.93.116.117 port 36872
Mar 15 13:28:05 sshd[1476]: User ubuntu not allowed because account is locked
Mar 15 13:36:37 sshd[1145]: Received signal 15; terminating.

當我創建 another_user 並設置密鑰身份驗證，禁用 ssh 密碼登錄時，我忘記為其指定非空密碼。因此，這可能是該使用者被鎖定的原因。無論如何，我現在正在尋找一種方法來解鎖使用者 ubuntu，至少是暫時的，看看是否能解決 ssh 訪問問題。但是，如您所見，我不能使用系統命令，我需要能夠通過直接編輯系統文件來做到這一點。

更改一個文件中的一個字元就足夠了，以使使用者ubuntu再次登錄：

$ cd /path/to/mounted/volume
$ sudo nano etc/shadow

# Searh for the row that starts with "ubuntu:!"
# Change the "!" to "*", save, exit

將捲重新附加到損壞的實例並啟動它後，現在可以使用使用者 ubuntu 正常登錄。我仍然不知道為什麼這個使用者被自動鎖定。關於創建的另一個使用者，我假設它被鎖定，因為它的密碼為空，但我沒有參考來證明它。

引用自：https://unix.stackexchange.com/questions/573039