Detailed explanation of how to configure static IP in Centos8

After installing centos 8, the following error will appear when restarting the network

The error message is as follows:

Failed to start network.service: Unit network.service not found.

It means that the network service cannot be restarted because the network.service network service cannot be found.

On rhel8 (including centos8), there are no script files in /etc/sysconfig/network-scripts/, and there is no traditional network.service. Therefore, network configuration can only be performed through other methods, including the NM command tool set. In other words, on rhel8, NM must be turned on, otherwise the network cannot be used.

Manually configure static IP

cat /etc/sysconfig/network-scripts/ifcfg-ens32
TYPE=Ethernet
PROXY_METHOD=none
BROWSER_ONLY=no
BOOTPROTO=static
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=ens32
UUID=066b4926-b40c-4c28-a5b4-2310d2b96613
DEVICE=ens32
ONBOOT=yes
IPADDR=192.168.1.200
NETMASK=255.255.255.0
GATEWAY=192.168.1.254
DNS1=223.5.5.5
PREFIX=24

Reload the network configuration using nmcli

nmcli c reload

Check

nmcli c
NAME UUID TYPE DEVICE
ens32 066b4926-b40c-4c28-a5b4-2310d2b96613 ethernet ens32

Added nmcli command

How to use nmcli

The usage of nmcli is very similar to the Linux ip command and Cisco switch command, and supports tab completion (see the Tips at the end of this article for details). You can also view help by using -h, --help, or help at the end of the command.

nmcli --help
Usage: nmcli [OPTIONS] OBJECT { COMMAND | help }
 
OPTIONS
-o[verview] overview mode (hide default values)
-t[erse] terse output
-p[retty] pretty output
-m[ode] tabular|multiline output mode
-c[colors] auto|yes|no whether to use colors in output
-f[ields] <field1,field2,...>|all|common specify fields to output
-g[et-values] <field1,field2,...>|all|common shortcut for -m tabular -t -f
-e[scape] yes|no escape columns separators in values
-a[sk] ask for missing parameters
-s[how-secrets] allow displaying passwords
-w[ait] <seconds> set timeout waiting for finishing operations
-v[ersion] show program version
-h[elp] print this help
 
OBJECT
g[eneral] NetworkManager's general status and operations
n[etworking] overall networking control
r[adio] NetworkManager radio switches
c[onnection] NetworkManager's connections
d[evice] devices managed by NetworkManager
a[gent] NetworkManager secret agent or polkit agent
m[onitor] monitor NetworkManager changes

There are two most commonly used commands in nmcli:

nmcli connection
Translated as connection, it can be understood as a configuration file, equivalent to ifcfg-ethX. Can be abbreviated as nmcli c

nmcli device
Translated as device, it can be understood as an actual network card (including physical network cards and virtual network cards). Can be abbreviated as nmcli d
In NM, there are two dimensions: connection and device, which is a many-to-one relationship. If you want to assign an IP address to a network card, NM must first be able to manage this network card. The network cards in the device (that is, those visible by nmcli d) are managed by NM. Next, you can configure multiple connections for a device (that is, what nmcli c can see), each connection can be understood as an ifcfg configuration file. Only one connection can be active on a device at a time. The connection can be switched via nmcli c up.

There are two states of connection:

• Active (with colored font): indicates that the connection is currently in effect
• Inactive (normal font): indicates that the connection is not currently valid.

There are four common states for a device:

• connected: It has been managed by NM and currently has an active connection
• disconnected: The device has been managed by NM, but currently has no active connection.
• unmanaged: Not managed by NM
• unavailable: unavailable, NM cannot be managed, usually occurs when the network card link is down (for example, ip link set ens32 down)

List of common nmcli commands

# View IP (similar to ifconfig, ip addr)
nmcli
 
# Create a connection, configure a static IP (equivalent to configuring ifcfg, where BOOTPROTO=none, and start it with ifup)
nmcli c add type ethernet con-name ens32 ifname ens32 ipv4.addr 192.168.1.100/24 ​​ipv4.gateway 192.168.1.1 ipv4.method manual
 
# Create a connection and configure a dynamic IP (equivalent to configuring ifcfg, where BOOTPROTO=dhcp and ifup is used to start the connection)
nmcli c add type ethernet con-name ens32 ifname ens32 ipv4.method auto

# Modify ip (non-interactive)
nmcli c modify ens32 ipv4.addr '192.168.1.200/24'
nmcli c up ens32

# Modify ip (interactive)
nmcli c edit ens32
nmcli> goto ipv4.addresses
nmcli ipv4.addresses> change
Edit 'addresses' value: 192.168.1.200/24
Do you also want to set 'ipv4.method' to 'manual'? [yes]: yes
nmcli ipv4> save
nmcli ipv4> activate
nmcli ipv4> quit

# Enable connection (equivalent to ifup)
nmcli c up ens32

# Stop connection (equivalent to ifdown)
nmcli c down

# Delete connection (similar to ifdown and delete ifcfg)
nmcli c delete ens32

# View the connection list nmcli c show

# View connection details nmcli c show ens32

# Reload all ifcfg or route to connection (will not take effect immediately)
nmcli c reload

# Reload the specified ifcfg or route to connection (will not take effect immediately)
nmcli c load /etc/sysconfig/network-scripts/ifcfg-ens32
nmcli c load /etc/sysconfig/network-scripts/route-ens32

# Connection takes effect immediately. There are three methods: nmcli c up ens32
nmcli d reapply ens32
nmcli d connect ens32

# View the device list nmcli d

# View all device detailed information nmcli d show

# View detailed information about the specified device nmcli d show ens32

# Activate the network card nmcli d connect ens32

# Disable wireless network (NM enables wireless network by default)
nmcli r all off

# Check the NM management status nmcli n

# Enable NM management nmcli n on

# Disable NM management (execute with caution)
nmcli n off

#Monitoring events nmcli m

# View the status of NM itself nmcli

# Check whether NM is available online nm-online

The ifcfg mentioned here refers to /etc/sysconfig/network-scripts/ifcfg-ens32 and /etc/sysconfig/network-scripts/route-ens32

nmcli connection key points

nmcli c show
NAME UUID TYPE DEVICE
ens32 066b4926-b40c-4c28-a5b4-2310d2b96613 ethernet ens32

• The first column is the connection name, referred to as con-name (note that con-name is not the network card name)
• The second column is the UUID of the connection
• The last column is the network card name (standardly called device name), which can be viewed through nmcil d

When operating on a connection, you need to specify an identifier, which can be con-name, UUID, or if an ifcfg file exists, you can also use the full path of ifcfg, i.e. /etc/sysconfig/network-scripts/ifcfg-ens32

nmcli c show ens32
nmcli c show cae3f1ef-e79a-46c3-8e0c-946b91a65e11
nmcli c show /etc/sysconfig/network-scripts/ifcfg-ens32

nmcli c con-name

It corresponds to the file name of ifcfg and NAME= in the content. This parameter indicates the name of the connection. It does not need to be the same as the network card name. You can create multiple connections for a device, but only one connection can be effective at the same time. When there are multiple connections, nmcli c delete deletes the current connection and automatically selects other connections of the same device to take its place. You can use nmcli c up to make the specified connection switch effective.
Note: Modifying con-name through nmcli c modify will only modify the NAME in the ifcfg file, but will not change the ifcfg file name.

nmcli c's ipv4.method

Corresponding to the BOOTPROTO of the ifcfg file content, the default value of ipv4.method is auto, which corresponds to BOOTPROTO=dhcp. If you specify the IP at this time, it may cause the network card to have both the IP assigned by DHCP and the static IP. Setting it to manual means BOOTPROTO=none, which means there is only a static IP.

Example: Creating a connection

nmcli c add type ethernet con-name ens32-test ifname ens32 ipv4.addresses '192.168.1.100/24,192.168.1.101/32' ipv4.routes '10.0.0.0/8 192.168.1.10,192.168.0.0/16 192.168.1.11' ipv4.gateway 192.168.1.254 ipv4.dns '8.8.8.8,4.4.4.4' ipv4.method manual

• type ethernet: When creating a connection, you must specify the type. There are many types, which can be viewed through nmcli c add type -h. Here, ethernet is specified.
• con-name ens32 ifname ens32: The first ethX indicates the name of the connection, which can be defined arbitrarily and does not need to be the same as the network card name; the second ethX indicates the network card name, which must be visible in nmcli d.
• ipv4.addresses '192.168.1.100/24,192.168.1.101/32': configure two IP addresses, 192.168.1.100/24 ​​and 192.168.1.101/32
• ipv4.gateway 192.168.1.254: The gateway is 192.168.1.254
• ipv4.dns '8.8.8.8,4.4.4.4': dns is 8.8.8.8 and 4.4.4.4
• ipv4.method manual: Configure static IP

The corresponding ifcfg and dns are

# /etc/sysconfig/network-scripts/ifcfg-ens32-test
TYPE=Ethernet
PROXY_METHOD=none
BROWSER_ONLY=no
BOOTPROTO=none
IPADDR=192.168.1.100
PREFIX=24
IPADDR1=192.168.1.101
PREFIX1=32
GATEWAY=192.168.1.254
DNS1=8.8.8.8
DNS2=4.4.4.4
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=ens32-test
UUID=9a10ad89-437c-4caa-949c-a394a6d28c8d
DEVICE=ens32
ONBOOT=yes
 
# /etc/resolv.conf
nameserver 8.8.8.8
nameserver 4.4.4.4

At this point, you should be able to see an additional connection through nmcli c

Note: If this is the first connection created for ethX, it will automatically take effect; if there is already a connection, it will not take effect automatically. You can execute nmcli c up ethX-test to switch it to take effect.

nmcli device Key Points

nmcli d connect ens32
NM manages the specified network card and refreshes the active connection corresponding to the network card (if the connection configuration has been modified before); if there is a connection but it is inactive, it automatically selects a connection and makes it active; if there is no connection, it automatically generates one and makes it active.

nmcli d disconnect ens32
Instruct NM to temporarily stop managing the specified network card. This operation will not change the link status of the actual network card, but will only make the corresponding connection inactive. If you restart the system, it will automatically connect again. In addition, if all connections of the network card are deleted manually, the status of the network card will automatically change to disconnected.

nmcli d reapply ens32
It is specifically used to refresh the connection, provided that the network card device is in the connected state, otherwise an error will be reported.

nmcli d set ens32 autoconnect yes|no managed yes|no
You can set whether to connect automatically and whether to manage automatically, but after testing it can only be used in the current boot state. If these two parameters are set to no and then the system is restarted, it will automatically return to the connected and managed yes states. So this command is not very useful. Note: If managed is set to no, nmcli c reload will read the configuration file, but it will not take effect immediately. Then, if nmcli c up ethX is executed, it will take effect immediately and managed will automatically change to yes.

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