Overview
By the end of this article you should be able to answer the following questions:
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ifcfg-{interface-name}
BOOTPROTO=”dhcp”
IPADDR0={ip-number}
GATEWAY0={ip-number}
NM_CONTROLLED=no
ONBOOT=’yes’
PREFIX=28
DNS1=8.8.8.8
The following directory houses connection config files for every single interface. These names of these files all follow the convention ifcfg-{interface-name}, in our case conly 2 files fit that naming convention:
$ ls -l /etc/sysconfig/network-scripts total 232 -rw-r--r--. 1 root root 321 Mar 14 19:23 ifcfg-enp0s3 -rw-r--r--. 1 root root 254 Jan 15 08:57 ifcfg-lo lrwxrwxrwx. 1 root root 24 Apr 3 16:19 ifdown -> ../../../usr/sbin/ifdown -rwxr-xr-x. 1 root root 627 Jan 15 08:57 ifdown-bnep -rwxr-xr-x. 1 root root 5817 Jan 15 08:57 ifdown-eth -rwxr-xr-x. 1 root root 6196 Mar 6 05:17 ifdown-ib . . ...etc
We can ignore the lo interface since that refers to the loopback interface, which is a software only implementation of an interface.
If we take a look at this config file, we see the following:
$ cat /etc/sysconfig/network-scripts/ifcfg-enp0s3 HWADDR="08:00:27:82:83:FC" # this is the interfaces mac address TYPE="Ethernet" # this means it is wired connection, as opposed to wifi BOOTPROTO="dhcp" # this means we are using dhcp DEFROUTE="yes" # ignore this PEERDNS="yes" # ignore this PEERROUTES="yes" # ignore this IPV4_FAILURE_FATAL="no" # ignore this IPV6INIT="yes" # ignore this IPV6_AUTOCONF="yes" # ignore this IPV6_DEFROUTE="yes" # ignore this IPV6_PEERDNS="yes" # ignore this IPV6_PEERROUTES="yes" # ignore this IPV6_FAILURE_FATAL="no" # ignore this NAME="enp0s3" UUID="c107488a-e080-4f46-a6a6-241d2e5e8846" ONBOOT="yes" # this means that the network must be up at bootup.
As you can see that this file does not give any of the following information:
- IPADDR0 – You can also have IPADDR1, IPADDR2,…etc
- GATEWAY0 – You can also have GATEWAY1, GATEWAY2,…etc
- PREFIX0 – This is the subnet mask, aka netmask, e.g. can have value 24. You can also have PREFIX1, PREFIX2,…etc
That is because BOOTPROTO setting is set to ”dhcp” rather than “none”, which means that the dhcp handles all this info.
You can edit this file directly, (if so then you will need to restart the interface using the ifdown and ifup command, which is covered further down), or you can use the gnome gui interface:
For example, while dhcp is enabled we have:
$ cat ifcfg-enp0s3 HWADDR="08:00:27:82:83:FC" TYPE="Ethernet" BOOTPROTO="dhcp" DEFROUTE="yes" IPV4_FAILURE_FATAL="no" IPV6INIT="yes" IPV6_AUTOCONF="yes" IPV6_DEFROUTE="yes" IPV6_FAILURE_FATAL="no" NAME="enp0s3" UUID="c107488a-e080-4f46-a6a6-241d2e5e8846" ONBOOT="yes" PEERDNS=yes PEERROUTES=yes IPV6_PEERDNS=yes IPV6_PEERROUTES=yes
Now if we use the gnome gui to disable dhcp and apply the following settings:
Then the config file changes to:
$ cat ifcfg-enp0s3 HWADDR="08:00:27:82:83:FC" TYPE="Ethernet" BOOTPROTO=none # DHCP is disabled DEFROUTE="yes" IPV4_FAILURE_FATAL="no" IPV6INIT="yes" IPV6_AUTOCONF="yes" IPV6_DEFROUTE="yes" IPV6_FAILURE_FATAL="no" NAME="enp0s3" UUID="c107488a-e080-4f46-a6a6-241d2e5e8846" ONBOOT="yes" IPADDR=192.168.1.10 # ip address is now static PREFIX=28 # prefix is now static GATEWAY=192.168.1.35 # gateway ip is now now static DNS1=8.8.8.8 # dns is now static. IPV6_PEERDNS=yes IPV6_PEERROUTES=yes
The resolv config file
This file is automatically generated (and used internally) by network manager. It is derived from the content in the network config file, e.g. ifcfg-enp0s3.
$ cat /etc/resolv.conf # Generated by NetworkManager search codingbee.dyndns.org nameserver 192.168.1.1
Never make any changes to the resolv.config file.
$ less /usr/share/doc/initscripts-*/sysconfig.txt
This is a help file that describes the role of various networking script files.
Stopping and starting an interface
If you make any changes to a network file, then remember that you need to restart the network interface card for the changes to take effect. this is done using the ifdown and ifup commands. Here it is in action:
$ nmcli con show NAME UUID TYPE DEVICE System enp0s3 ad2de184-098f-4eb8-92af-3e6c086f1186 802-3-ethernet enp0s3 $ ifdown enp0s3 Device 'enp0s3' successfully disconnected. $ nmcli con show NAME UUID TYPE DEVICE System enp0s3 ad2de184-098f-4eb8-92af-3e6c086f1186 802-3-ethernet -- $ ifup enp0s3 Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/4) $ nmcli con show NAME UUID TYPE DEVICE System enp0s3 ad2de184-098f-4eb8-92af-3e6c086f1186 802-3-ethernet enp0s3
Starting/stopping the interface will be reflected a tiny cross appearing on the network icon on the top right of the gnome interface. Also this will disconnect any ssh/putty sessions.
Here we used nmcli to view the status. we could have also used nmcli instead of ifup/ifdown commands:
$ nmcli con show NAME UUID TYPE DEVICE System enp0s3 ad2de184-098f-4eb8-92af-3e6c086f1186 802-3-ethernet enp0s3 $ nmcli con down "System enp0s3" Connection 'System enp0s3' successfully deactivated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/5) $ nmcli con up "System enp0s3" Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/6) $ nmcli con show NAME UUID TYPE DEVICE System enp0s3 ad2de184-098f-4eb8-92af-3e6c086f1186 802-3-ethernet enp0s3
Note, starting/stopping a network device using nmcli or ifup/ifdown won’t survive a reboot. In order to survive a reboot you need to edit the device’s configuration settings file, which is located in /etc/sysconfig/network-scripts/.
Alternatively you can make this persistant by using the nmcli command like this:
$ nmcli connection modify System\ enp0s3 connection.autoconnect no $ cat ifcfg-enp0s3 | grep ONBOOT ONBOOT=no $ nmcli connection modify System\ enp0s3 connection.autoconnect yes $ cat ifcfg-enp0s3 | grep ONBOOT ONBOOT=yes
the nmcli command is long wielded, but luckily you can use the tab+tab autocomplete to make things easier.