CentOS 7 – Watch out for nmtui

It would appear that I have been caught out twice now due to the way that nmtui (Network Manager Text User Interface) works.  I have been messing around with various internal sandboxed networks in my VM environment and (I can only assume ion my haste), I have entered the IP address of a second NIC without full regard for the on screen prompts.

In nmtui, there is one field missing which is quite common in many other tools.  Take a look at the following and tell me what’s missing;


So what field do you think is missing?

Now although the information is all on screen in the screenshot above, there is one thing that may not be obvious.  In the Addresses field you specify not only the IP address but also the subnet mask in CIDR (which stands for Classless Inter-Domain Routing) notation.

IF, you happen to enter and IP address without thinking about it and don’t specify the netmask or CIDR, nmtui assumes that you are only referring to a /32, a.k.a. a netmask of, which for the uninitiated means just that IP.  If assumes that there is nothing beyond that IP address.  It’s world is only itself.

In the good old days where I used to configure the IP address via ifcfg-eth* files, I also remembered to enter the NETMASK= line, and therefore never had this issue.

Anyway rant over.  Hopefully twice is enough, because if nothing else, if I have name resolutions errors in my logs again, I will be making sure my netmask is set correctly, before thinking that tomcat is having issues.


Featured image credit:  Thanks to versageek for making the Network Spagetti image available on Flickr.com.

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