In Linux system, using the usermod command to add users to the secondary group is: 1. Execute the sudousermod-a-G group name username command to add, where -a means append to avoid overwriting the original secondary group; 2. Use groups username or grep group name /etc/group to verify whether the operation is successful; 3. Note that the modification only takes effect after the user logs in again, and the main group modification should use the -g parameter; 4. You can also manually edit the /etc/group file to add users, but be careful to avoid system abnormalities caused by format errors.

To migrate from CentOS8 to AlmaLinux or RockyLinux, follow the clear steps. First, choose AlmaLinux (suitable for long-term enterprise support) or RockyLinux (emphasizing exactly the same as RHEL) according to your needs. Secondly, prepare the system environment: update the software package, back up key data, check third-party repositories and disk space. Then, the conversion is automatically completed using the official migration script. RockyLinux needs to clone the repository and run the switch-to-rocky.sh script. AlmaLinux replaces the repository and upgrades with one click through the remote deployment script. Finally, verify system information, clean up residual packets, and update GRUB and ini if ??necessary

To correctly install the local RPM file and handle dependencies, you should first use dnf to install it directly, because it can automatically obtain the required dependencies from the configured repository; if the system does not support dnf, you can use yum's localinstall command instead; if the dependency cannot be resolved, you can manually download and install all related packages; finally, you can also forcefully ignore the dependency installation, but this method is not recommended. 1. Use sudodnfinstall./package-name.rpm to automatically resolve dependencies; 2. If there is no dnf, you can use sudoyumlocalinstall./package-name.rpm; 3. Force installation and execute sudorpm-ivh--nod

How to set a static IP address using nmcli on CentOS8 or 9? 1. First run the nmcliconnectionshow and ipa commands to view the current network interface and its configuration; 2. Use the nmcliconnectionmodify command to modify the connection configuration, specify parameters such as ipv4.methodmanual, ipv4.addresses (such as 192.168.1.100/24), ipv4.gateway (such as 192.168.1.1), and ipv4.dns (such as 8.8.8.8). 3. Run the nmcliconnectiondown and up commands to restart the connection to make the changes take effect, or

The current running mode of SELinux can be viewed through the command line. Use getenforce command to directly display the current status, and the output is Enforcing, Permissive or Disabled; view the /etc/selinux/config file to know the default startup mode; temporarily change the mode can be setenforce1 (enforcing) or setenforce0 (permissive), but restore the configuration file settings after restart; in actual applications, you need to pay attention to service compatibility issues, and switch modes to troubleshoot problems if necessary.

Installing and configuring fail2ban on CentOS is not complicated, it mainly includes the following steps: 1. Install fail2ban using yum; 2. Manually enable and start the service; 3. Create a jail.local file for custom configuration; 4. Set SSH defense rules, including enabling sshd, specifying the blocking time and retry times; 5. Configure firewalld as an action actuator; 6. Regularly check the blocking IP and logs. Fail2ban detects abnormal login behavior through monitoring logs and automatically blocks suspicious IPs. Its core mechanism relies on key parameters such as bantime (banned time), findtime (statistic window time) and maxretry (maximum failure number).

AminimalinstallofCentOSisalightweightsetupthatincludesonlyessentialcomponents,makingitidealforserversorsystemsrequiringfullcontrol.Itcontainscoreutilitieslikebash,yum/dnf,networkingtools,andsecuritypackages,whileexcludingdesktopenvironments,webserver

KernelCare and kpatch are both tools for implementing hot patches in the Linux kernel, but the applicable scenarios are different. 1. KernelCare is a commercial service that supports CentOS, RHEL, Ubuntu and Debian, automatically applies patches without restarting, and is suitable for hosting service providers and enterprise production environments; 2. kpatch is an open source tool developed by Red Hat. It is based on the ftrace framework and requires manual construction of patch modules. It is suitable for RHEL and compatible systems, and is suitable for organizations that need to finely control the patch process or use customized kernels. When choosing, automation requirements, system distribution, whether official support is required, and the degree of control over open source tools should be considered. Neither of them can fix all vulnerabilities, some still need to be restarted, and