The Problem
Server failed to login through ssh with below errors.
From ssh client:
$ ssh -vvv root@10.131.12.10 OpenSSH_7.6p1, LibreSSL 2.6.2 debug1: Reading configuration data /etc/ssh/ssh_config debug1: /etc/ssh/ssh_config line 48: Applying options for * debug2: ssh_connect_direct: needpriv 0 debug1: Connecting to 10.131.12.10 port 22. debug1: Connection established. debug1: key_load_public: No such file or directory debug1: identity file /Users/yaozhenqiang/.ssh/id_rsa type -1 debug1: key_load_public: No such file or directory debug1: identity file /Users/yaozhenqiang/.ssh/id_rsa-cert type -1 debug1: key_load_public: No such file or directory debug1: identity file /Users/yaozhenqiang/.ssh/id_dsa type -1 debug1: key_load_public: No such file or directory debug1: identity file /Users/yaozhenqiang/.ssh/id_dsa-cert type -1 debug1: key_load_public: No such file or directory debug1: identity file /Users/yaozhenqiang/.ssh/id_ecdsa type -1 debug1: key_load_public: No such file or directory debug1: identity file /Users/yaozhenqiang/.ssh/id_ecdsa-cert type -1 debug1: key_load_public: No such file or directory debug1: identity file /Users/yaozhenqiang/.ssh/id_ed25519 type -1 debug1: key_load_public: No such file or directory debug1: identity file /Users/yaozhenqiang/.ssh/id_ed25519-cert type -1 debug1: Local version string SSH-2.0-OpenSSH_7.6 ssh_exchange_identification: read: Connection reset by peer
From ssh server:
# /usr/sbin/sshd -D -ddd ....snip.... debug1: Bind to port 22 on ::. Server listening on :: port 22. debug3: fd 5 is not O_NONBLOCK debug1: Server will not fork when running in debugging mode. debug3: send_rexec_state: entering fd = 8 config len 583 debug3: ssh_msg_send: type 0 debug3: send_rexec_state: done debug1: rexec start in 5 out 5 newsock 5 pipe -1 sock 8 debug1: inetd sockets after dupping: 3, 3 debug1: Connection refused by tcp wrapper
The Solution
ssh connection was refused by tcp wrapper. To determine if a client machine is allowed to connect to SSH, TCP wrappers refer the following two files:
- /etc/hosts.deny
- /etc/hosts.allow
Please follow below steps to determine which IP address of ssh client was refused by TCP wrapper:
1. Comment out all lines in /etc/hosts.deny and /etc/hosts.allow
2. Now ssh login should be working normally:
$ ssh root@10.131.12.10 root@10.131.12.10's password: Last login: Fri Mar 16 11:14:44 2018 from server1
3. Go to ssh server, open /var/log/secure and navigate to the messages around the time stamp “Last login: Fri Mar 16 11:14:44 2018” showing in step 2, then we can get the IP address of ssh client that was refused by TCP wrapper previously.
4. Restore /etc/hosts.deny and /etc/hosts.allow and add below line in /etc/hosts.allow (Let’s say, 192.168.1.2 is the IP address we get in step 3)
# vi /etc/hosts.allow sshd:192.168.1.2:allow
5. Verify if ssh login is working.