How to Configure and Manage Network Connections Using ‘nmcli’ Tool

As a Linux administrator you’ve got various tools to use in order to configure your network connections, such as: nmtui, your NetworkManager with GNOME graphical user interface and of course nmcli (network manager command line tool).

I have seen many administrators using nmtui for simplicity. However using nmcli saves your time, gives you confidence, can use it in scripts and it’s the first tool to use in order to troubleshoot your Linux server networking and bring back rapidly its functionality.

Seeing many comments asking help about nmcli, I decided to write this article. Of course you should always read carefully man pages (its the No1 help for you). My aim is to save your time and show you some hints.

The syntax of nmcli is:

# nmcli [OPTIONS] OBJECT {COMMAND | help}

Where OBJECT is one of: general, networking, radio, connection, device, agent.

A good starting point would be to check our devices:

# nmcli dev status

DEVICE      TYPE      STATE         CONNECTION 
docker0     bridge    connected     docker0    
virbr0      bridge    connected     virbr0     
enp0s3      ethernet  connected     enp0s3     
virbr0-nic  ethernet  disconnected  --         
lo          loopback  unmanaged     --         

As we can see in the first column is a list of our network devices. We have one network cards with name enp0s3. In your machine you could see other names.

Naming depends on the type of the network card (if it is onboard, pci card , etc). In the last column we see our configuration files which is used by our devices in order to connect to the network.

It is simple to understand that our devices by themselves can do nothing. They need us to make a configuration file to tell them how to achieve network connectivity. We call these files also as “connection profiles”. We find them in /etc/sysconfig/network-scripts directory.

# cd /etc/sysconfig/network-scripts/
# ls

Sample Output

ifcfg-enp0s3  ifdown-isdn      ifup          ifup-plip      ifup-tunnel
ifcfg-lo      ifdown-post      ifup-aliases  ifup-plusb     ifup-wireless
ifdown        ifdown-ppp       ifup-bnep     ifup-post      init.ipv6-global
ifdown-bnep   ifdown-routes    ifup-eth      ifup-ppp       network-functions
ifdown-eth    ifdown-sit       ifup-ib       ifup-routes    network-functions-ipv6
ifdown-ib     ifdown-Team      ifup-ippp     ifup-sit
ifdown-ippp   ifdown-TeamPort  ifup-ipv6     ifup-Team
ifdown-ipv6   ifdown-tunnel    ifup-isdn     ifup-TeamPort

As you can see here the files with name starting with ifcfg- (interface configuration) are connection profiles. When we create a new connection or modify an existing one with nmcli or nmtui, the results are saved here as connection profiles.

Ι ‘ll show you two of them from my machine, one with a dhcp configuration and one with static ip.

# cat ifcfg-static1
# cat ifcfg-Myoffice1

We realize that some properties have different values and some others don’t exist if it isn’t necessary. Let’s have a quick look to most important of them.

1. TYPE, we have ethernet type here. We could have wifi, team, bond and others.
2. DEVICE, the name of the network device which is associated with this profile.
3. BOOTPROTO, if it has value “dhcp” then our connection profile takes dynamic IP from dhcp server, if it has value “none” then it takes no dynamic IP and probably whe assign a static IP.
4. IPADDR, is the static IP we assign to our profile.
5. PREFIX, the subnet mask. A value of 24 means 255.255.255.0. You can understand better the subnet mask if you write down its binary format. For example values of 16, 24, 26 means that the first 16, 24 or 26 bits respectively are 1 and the rest 0, defining exactly what the network address is and what is the range of ip which can be assigned.
6. GATEWAY, the gateway IP.
7. DNS1, DNS2, two dns servers we want to use.
8. ONBOOT, if it has value “yes” it means, that on boot our computer will read this profile and try to assign it to its device.

Now, let’s move on and check our connections:

# nmcli con show

The last column of devices helps us understand which connection is “UP” and running and which is not. In the above image you can see the two connections which are active: Myoffice1 and enp0s8.

Hint: If you want to see only the active connections, type:

# nmcli con show -a

Hint: You can use the auto-complete hitting Tab when you use nmcli, but is better to use minimal format of the command. Thus, the following commands are equal:

# nmcli connection show
# nmcli con show
# nmcli c s

If I check the ip addresses of my devices:

# ip a

I see that my device enp0s3 took the 192.168.1.6 IP from dhcp server, because the connection profile Myoffice1 which is up has a dhcp configuration. If I bring “up” my connection profile with name static1 then my device will take the static IP 192.168.1.40 as it is defined in the connection profile.

# nmcli con down Myoffice1 ; nmcli con up static1
# nmcli con show

Let’s see the IP address again:

# ip a

We can make our first connection profile. The minimum properties we must define are type, ifname and con-name:

1. type – for the type of connection.
2. ifname – for the device name which is assigned our connection.
3. con-name – for the connection name.

Let’s make a new ethernet connection with name Myhome1, assigned to device enp0s3:

# nmcli con add type ethernet con-name Myhome1 ifname enp0s3

Check its configuration:

# cat ifcfg-Myhome1

As you can see it has BOOTPROTO=dhcp, because we didn’t give any static ip address.

Hint: We can modify any connection with the “nmcli con mod“ command. However if you modify a dhcp connection and change it to static don’t forget to change its “ipv4.method” from “auto” to “manual”. Otherwise you will end up with two IP addresses: one from dhcp server and the static one.

Let’s make a new Ethernet connection profile with name static2, which will be assigned to device enp0s3, with static IP 192.168.1.50, subnet mask 255.255.255.0=24 and gateway 192.168.1.1.

# nmcli con add type ethernet con-name static2 ifname enp0s3 ip4 192.168.1.50/24 gw4 192.168.1.1

Check its configuration:

# cat ifcfg-static2

Let’s modify the last connection profile and add two dns servers.

# nmcli con mod static2 ipv4.dns “8.8.8.8 8.8.4.4”

Hint: There is something here you must pay attention: the properties for IP address and gateway have different names when you add and when you modify a connection. When you add connections you use “ip4” and “gw4”, while when you modify them you use “ipv4” and “gwv4”.

Now let’s bring up this connection profile:

# nmcli con down static1 ; nmcli con up static2

As you can see, the device enp0s3 has now IP address 192.168.1.50.

# ip a

Hint: There are a lot of properties you can modify. If you don’t remember them by heart you can help yourself by typing “nmcli con show” and after that the connection name:

# nmcli con show static2

You can modify all these properties written in lowercase.

For example: when you bring down a connection profile, the NetworkManager searches for another connection profile and brings it up automatically. (I leave it as exercise to check it). If you don’t want your connection profile to autoconnect:

# nmcli con mod static2 connection.autoconnect no

The last exercise is very usefull: you made a connection profile but you want it to be used by specific users. It’s good to classify your users!

We let only user stella to use this profile:

# nmcli con mod static2 connection.permissions stella

Hint: If you want to give permissions to more than one users, you must type user:user1,user2 without blank space between them:

# nmcli con mod static2 connection.permissions user:stella,john

If you login as another user you can’t bring “up” this connection profile:

# nmcli con show
# nmcli con up static2
# ls /etc/sysconfig/network-scripts

An error message says that connection ‘static2’ does not exist, even if we see that it exists. That’s because current user has no permissions to bring up this connection.

Conclusion: don’t hesitate to use nmcli. It’s easy and helpful.