Linux sysadmin basics: Start NIC at boot
![Network Interface Card](/sysadmin/sites/default/files/styles/full/public/2019-11/Fast_Ethernet_PCI_Network_Interface_Card_SN5100TX_%28VIA_VT86C100A%29%20Cropped_0.jpg?itok=yDsaz3Xv)
It might surprise you to know that if you forget to flip the network interface card (NIC) switch to the ON position (shown in the image below) during installation, your Red Hat-based system will boot with the NIC disconnected:
But, don't worry, in this article I'll show you how to set the NIC to connect on every boot and I'll show you how to disable/enable your NIC on demand.
If your NIC isn't enabled at startup, you have to edit the /etc/sysconfig/network-scripts/ifcfg-NIC_name
file, where NIC_name is your system's NIC device name. In my case, it's enp0s3. Yours might be eth0, eth1, em1, etc. List your network devices and their IP addresses with the ip addr
command:
$ ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 08:00:27:81:d0:2d brd ff:ff:ff:ff:ff:ff
3: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
link/ether 52:54:00:4e:69:84 brd ff:ff:ff:ff:ff:ff
inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
valid_lft forever preferred_lft forever
4: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc fq_codel master virbr0 state DOWN group default qlen 1000
link/ether 52:54:00:4e:69:84 brd ff:ff:ff:ff:ff:ff
Note that my primary NIC (enp0s3) has no assigned IP address. I have virtual NICs because my Red Hat Enterprise Linux 8 system is a VirtualBox virtual machine. After you've figured out what your physical NIC's name is, you can now edit its interface configuration file:
$ sudo vi /etc/sysconfig/network-scripts/ifcfg-enp0s3
and change the ONBOOT="no"
entry to ONBOOT="yes"
as shown below:
TYPE="Ethernet"
PROXY_METHOD="none"
BROWSER_ONLY="no"
BOOTPROTO="dhcp"
DEFROUTE="yes"
IPV4_FAILURE_FATAL="no"
IPV6INIT="yes"
IPV6_AUTOCONF="yes"
IPV6_DEFROUTE="yes"
IPV6_FAILURE_FATAL="no"
IPV6_ADDR_GEN_MODE="stable-privacy"
NAME="enp0s3"
UUID="77cb083f-2ad3-42e2-9070-697cb24edf94"
DEVICE="enp0s3"
ONBOOT="yes"
Save and exit the file.
You don't need to reboot to start the NIC, but after you make this change, the primary NIC will be on and connected upon all subsequent boots.
To enable the NIC, use the ifup
command:
ifup enp0s3
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/5)
Now the ip addr
command displays the enp0s3 device with an IP address:
$ ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 08:00:27:81:d0:2d brd ff:ff:ff:ff:ff:ff
inet 192.168.1.64/24 brd 192.168.1.255 scope global dynamic noprefixroute enp0s3
valid_lft 86266sec preferred_lft 86266sec
inet6 2600:1702:a40:88b0:c30:ce7e:9319:9fe0/64 scope global dynamic noprefixroute
valid_lft 3467sec preferred_lft 3467sec
inet6 fe80::9b21:3498:b83c:f3d4/64 scope link noprefixroute
valid_lft forever preferred_lft forever
3: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
link/ether 52:54:00:4e:69:84 brd ff:ff:ff:ff:ff:ff
inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
valid_lft forever preferred_lft forever
4: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc fq_codel master virbr0 state DOWN group default qlen 1000
link/ether 52:54:00:4e:69:84 brd ff:ff:ff:ff:ff:ff
To disable a NIC, use the ifdown
command. Please note that issuing this command from a remote system will terminate your session:
ifdown enp0s3
Connection 'enp0s3' successfully deactivated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/5)
That's a wrap
It's frustrating to encounter a Linux system that has no network connection. It's more frustrating to have to connect to a virtual KVM or to walk up to the console to fix it. It's easy to miss the switch during installation, I've missed it myself. Now you know how to fix the problem and have your system network-connected on every boot, so before you drive yourself crazy with troubleshooting steps, try the ifup
command to see if that's your easy fix.
Takeaways: ifup, ifdown, /etc/sysconfig/network-scripts/ifcfg-NIC_name
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Ken Hess
Ken has used Red Hat Linux since 1996 and has written ebooks, whitepapers, actual books, thousands of exam review questions, and hundreds of articles on open source and other topics. Ken also has 20+ years of experience as an enterprise sysadmin with Unix, Linux, Windows, and Virtualization. More about me