When the CentOS server cannot be connected to the network, you can follow the following steps to check: 1. Check the status of the network interface, use iplinkshow to confirm whether the interface is enabled, if not enabled, use sudoiplinksetup to start, and use ipaddrshow to check the IP allocation status; 2. If it is in DHCP mode, run sudodhclient to obtain the IP. If it is static configuration, check the IP, gateway and DNS settings in /etc/sysconfig/network-scripts/ifcfg- and restart the network service; 3. Check the routing table iprouteshow to ensure that there is a default gateway. If there is no, add it temporarily or modify GATEWAY in the configuration file.

The key to enabling EPEL repository is to select the correct installation method according to the system version. First, confirm the system type and version, and use the command cat/etc/os-release to obtain information; second, enable EPEL through dnfinstallepel-release on CentOS/RockyLinux, and the 8 and 9 version commands are the same; third, you need to manually download the corresponding version of the .repo file and install it on RHEL; fourth, you can re-import the GPG key when encountering problems. Note that the old version may not be supported, and you can also consider enabling epel-next to obtain the test package. After completing the above steps, use dnfrepolist to verify that the EPEL repository is successfully added.

The steps to mount a new hard disk and realize automatic mount on the computer are as follows: 1. Use lsblk, fdisk-l or blkid to confirm the device path and UUID of the new hard disk. It is recommended to use UUID to ensure stability; 2. Create a mount point directory, such as /mnt/data, and set appropriate permissions; 3. Edit the /etc/fstab file, add a line of configuration, the format is UUID=hard disk UUID mount point file system type defaults02, note that the sixth column of the XFS file system is 0; 4. Use sudomount-a and df-h to confirm that it is correct to avoid errors after restart; 5. If there is a problem, check the file system type, mount point exists or enter reco based on the error message.

SELinux context errors will cause the service to fail to access the file. The solution is as follows: 1. Use chcon to temporarily modify, such as chcon-thttpd_sys_content_t/var/www/html/index.html, but it is invalid after restart; 2. Use semanagefcontext to set permanent rules, such as semanagefcontext-a-thttpd_sys_content_t"/opt/myapp(/.*)?", and then run the restorecon application rules; 3. View the file context through ls-Z and analyze the process context in combination with ps-eZ; 4.

To update all software packages on the CentOS system, you can use yum (CentOS7) or dnf (CentOS8 and above). The specific steps are as follows: 1. Check for available updates and use "sudoyumcheck-update" or "sudodnfcheck-update" to list the packages to be updated; 2. Execute the system-wide update, and use "sudoyumupdate-y" or "sudodnfupgrade--allowerasing" commands to upgrade, where the -y parameter is automatically confirmed, and --allowerasing allows the deletion of conflicting packages; 3. If the update involves a new kernel, the system needs to be restarted to take effect, and "unam can be used to use "

The key to modifying the DNS configuration of /etc/resolv.conf is to master the steps and precautions. The file needs to be changed because the system uses its specified DNS by default for domain name resolution. When changing more stable or privacy-protected DNS (such as 8.8.8.8, 1.1.1), it needs to be edited manually; nano or vim can be used to open the file and modify the nameserver entry; after saving and exiting, some systems need to restart the network service to take effect; however, it should be noted that if the system uses systemd-resolved or DHCP to automatically obtain the configuration, the direct modification may be overwritten. The corresponding configuration should be adjusted before locking the file or restarting the service; in addition, up to two or three DNS addresses can be added, the order affects

The key to updating the CentOS kernel is to use the ELRepo repository and set up the startup items correctly. 1. First run uname-r to view the current kernel version; 2. Install the ELRepo repository and import the key; 3. Use yum to install kernel-lt (long-term support version) or kernel-ml (main version); 4. After the installation is completed, check the available kernels through the awk command and use grub2-set-default to set the default startup item; 5. Generate a new GRUB configuration file grub2-mkconfig-o/boot/grub2/grub.cfg; 6. Finally restart the system and run uname-r again to confirm whether the kernel version is effective. The whole process requires

If the service starts, the steps should be checked: 1. Check the service status and logs, use systemctlstatus to confirm the failed status and use journalctl or log files to find error information; 2. Check whether the configuration file is correct, use the built-in tools to verify, roll back the old version, and troubleshoot segment by segment; 3. Verify whether the dependencies are satisfied, including database connections, environment variables, system libraries and associated service startup sequence; 4. Check permissions and SELinux/AppArmor restrictions to ensure that the running account has sufficient permissions and test whether the security module intercepts operations.