Home / ubuntu / Questions / 1401436
In Process
Bartender1382
Asked: 2022-04-08 18:27:07 +0800 CST

Suddenly SSH stopped working, but selectively and I can't figure out how to fix it

  • 772

I cannot SSH into my server, but I can view all its virtual webpages, FTP in, etc.

At home, I have an Ubuntu 18.04 server, a Mac, and my iPhone.

I am constantly ssh-ing into the ubuntu server from all my devices, via the internal IP address 192.X.X.X and my real-world IP address. I have confirmed that my router passes ports 20 thru 22 to the server via its reserved internal IP address.

Suddenly, I cannot ssh into the server via my Mac. Neither from the internal nor external IP address.

My iPhone can ssh into the server via the local IP address only.

Know very little about ubuntu/linix. This server has been running for over a year, and I just can't figure how to figure out where my problem is, nor fix it.

The only hint I have is that in the auth.log it shows my iPhone logging in via the local IP. And the only failures I see in auth.log is many attempts from the outside world.

I wonder if someone got in and broke something?

Could someone give me a clue of where to start, or what I should look for?

ssh

1 Answers

  1. the only failures I see in auth.log is many attempts from the outside world

    That is probably the reason that you cannot login to your server: Most ssh servers block a user after certain (usually 5) fail attempts. This is a built in security feature to avoid brute force breaking into the server.

    To unban the IP do the following on you server:

    Suppose the banned IP is 1.2.3.4 and you are using fail2ban:

    iptables -S | grep 1.2.3.4

    If the IP is banned you see a line like:

    -A f2b-sshd -s 1.2.3.4/32 -j REJECT --reject-with icmp-port-unreachable

    To unban run:

     iptables -D  f2b-sshd -s 1.2.3.4/32 -j REJECT --reject-with icmp-port-unreachable

    If that did not solve the problem banned, then run:

    fail2ban-client set sshd  unbanip 1.2.3.4
    • 1