當CentOS服務(wù)器無法聯(lián)網(wǎng)時，可按以下步驟排查：1.檢查網(wǎng)絡(luò)接口狀態(tài)，使用ip link show確認接口是否啟用，若未啟用則用sudo ip link set <interface_name> up啟動，并用ip addr show查看IP分配情況；2.若為DHCP模式，運行sudo dhclient <interface_name>獲取IP，若為靜態(tài)配置，需檢查/etc/sysconfig/network-scripts/ifcfg-<interface_name>中的IP、網(wǎng)關(guān)和DNS設(shè)置并重啟網(wǎng)絡(luò)服務(wù)；3.檢查路由表ip route show，確保存在默認網(wǎng)關(guān)，無則臨時添加或在配置文件中修改GATEWAY=；4.查看/etc/resolv.conf中的DNS配置，可手動添加如8.8.8.8等公共DNS進行測試；5.檢查firewalld狀態(tài)，必要時開放端口或暫時關(guān)閉防火墻測試連接；6.檢查SELinux狀態(tài)，若為enforcing模式可切換至permissive模式排除干擾。通過以上步驟通?？山鉀Q大部分網(wǎng)絡(luò)問題。

If your CentOS server has no network connection, there are a few common culprits—misconfigured settings, downed interfaces, or firewall issues. The good news is that most of these can be diagnosed and fixed quickly with a few basic commands and checks.

Check the Network Interface Status

First things first: make sure the network interface is actually up and recognized by the system. You can use the ip command to check:

ip link show

Look for an interface like eth0, ens33, or something similar. If it says DOWN, bring it up with:

sudo ip link set <interface_name> up

Also, verify if it received an IP address using:

ip addr show

If there's no IP address assigned, you might have a problem with DHCP or static configuration.

• For DHCP, try restarting the service:

  sudo dhclient <interface_name>

• For static setups, double-check /etc/sysconfig/network-scripts/ifcfg-<interface_name> for correct IP, gateway, and DNS entries.

Don’t forget to restart the network service after any changes:

sudo systemctl restart NetworkManager
# or if you're using the older network service:
sudo systemctl restart network

Verify DNS and Routing Settings

Even if the interface looks fine, the server might still not be able to reach the outside world due to routing or DNS problems.

Start by checking the routing table:

ip route show

Make sure there’s a default route pointing to a valid gateway. If not, add one temporarily:

sudo ip route add default via <gateway_ip> dev <interface_name>

To make this permanent, update the GATEWAY= line in your interface config file.

For DNS issues, look at /etc/resolv.conf. It should contain lines like:

nameserver 8.8.8.8
nameserver 8.8.4.4

You can temporarily test different DNS servers by editing this file directly. Just keep in mind that some systems regenerate this file automatically based on other network settings.

Check Firewall and SELinux

Sometimes the system itself blocks outgoing traffic without you realizing it. The main suspects here are firewalld and SELinux.

To see if firewalld is running:

sudo systemctl status firewalld

If it’s active, allow specific services or ports as needed:

sudo firewall-cmd --add-port=80/tcp --permanent
sudo firewall-cmd --reload

Or temporarily disable it to test connectivity:

sudo systemctl stop firewalld

SELinux doesn't usually block network access outright, but it can interfere depending on what services you're running. To check its status:

sestatus

If it's enforcing, try switching it to permissive mode:

sudo setenforce 0

Then test your network again. If it works now, dig into SELinux policies later—you don’t want to leave it disabled permanently.

That’s a solid starting point for troubleshooting network issues on a CentOS server. These steps cover physical layer problems, IP configuration, routing, DNS, and basic firewall interference. Fixing one or two of these areas often gets things back online.基本上就這些.

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