I have a monitoring server that requires the SSH connection details of a non-sudo user account of each box it monitors. Is there a way that I can configure a specific user account such that it can only be logged into from a specific IP (or better yet hostname)? I do not want to restrict the ability of other users on the server to be able to connect from other addresses (otherwise I'd just use a firewall), or use password authentication for the monitoring service only.
man sshd_config. There is possibility to add
AllowUsers block where you can specify both user and host like this:
AllowUsers user@host # or IP
Of course you need to specify also other users you want to allow login from, if you have some.
Another solution (depends on bug fixes!)
As I think about it once more, there is possibility to modify your
sshd_config like this:
Match Host !hostname DenyUsers user Match Host hostname AllowUsers user
This would easily block all users except from
hostname and from everywhere else it would block
BUT it doesn't work, because of few bugs reported upstream  . But we got it promised it will get fixed in next release.
You can use wildcards for the AllowUsers line on the
/etc/ssh/sshd_config file. So it would be feasible to add the line:
To allow everyone from that IP address or hostname access.
service ssh restart
Once you've made the changes, so long as you're on a version before 15.04. 15.04 uses systemd now, so has a different mechanism for controlling services.
According to man pages, this should work:
I tested this on Debian and it seemed to work correctly.
Since this is the top search result in google, I think people should also be aware of setting permissions in the
/etc/hosts.allow file (curtesy of Cameron Oltmann's blog post on the matter):
To limit ssh access to a linux box based on originating IP address, edit /etc/hosts.allow:
sshd : localhost : allow sshd : 192.168.0. : allow sshd : 18.104.22.168 : allow sshd : mydomain.net : allow sshd : ALL : deny
The above entry will allow ssh access from localhost, the 192.168.0.x subnet, the single IP address 22.214.171.124, and mydomain.net (assuming mydomain.net has a ptr record in place to facilitate reverse lookup). All other IP addresses will be denied access to sshd.
Notes: You can allow or deny based on ip address, subnet, or hostname. List rules in order of most to least specific. The file only gets read until a matching line is found, so if you start with ssdh : ALL : deny, no ssh connections will be allowed.
And you should be able to use
user@address in this file, per this lifewire.com link:
The more complex forms daemon@host and user@host are explained in the sections on server endpoint patterns and on client username lookups, respectively.