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Diffstat (limited to 'vimwiki/Blocked IP Addresses.md')
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diff --git a/vimwiki/Blocked IP Addresses.md b/vimwiki/Blocked IP Addresses.md new file mode 100644 index 0000000..6705f49 --- /dev/null +++ b/vimwiki/Blocked IP Addresses.md @@ -0,0 +1,19 @@ +An application called `fail2ban` blocks IP addresses with repeated failed login attempts. +If a user is locked out of ssh connections, this is usually why. + +If you suspect this has happened to someone, you need to know which cluster address they are trying to +log in to and ideally what IP address they are coming in from. Each machine that runs an ssh server +has its own fail2ban list. + +As root on the machine that the user is trying to log in to, do + +`fail2ban-client set sshd unbanip IPADDRESS` + +Note that normal users log in to both headnode1 and headnode2, so the problem may show up on one or +both of these machines. It can’t hurt to unban an IP that is not banned, so you can just do e.g. + +`sudo pdsh –w ‘headnode[1-2]’ fail2ban-client set sshd unbanip IPADDRESS` + +which will unban the IP on both head nodes2. If you have a problem working out the IP that’s banned, +try looking at `/var/log/secure.log` on the login machine. + |