What should I do if the yum command cannot be used in Linux?

The key to configuring a security group and firewall for cloud instances is to understand the traffic control logic and follow the principle of least permissions. 1. The security group is equivalent to a virtual firewall. It is used to control network traffic in and out of the instance. Only the necessary ports should be opened and the source IP should be restricted; 2. When setting inbound rules, SSH should be restricted to specific IPs. HTTP/HTTPS can be opened to the external network or whitelisted, and the database ports should not be opened to the external network; 3. Outbound rules allow all by default. In the initial stage, it is recommended to keep the default, and gradually tighten it in the future to avoid affecting system updates and service access; 4. Frequently asked questions to check the security group binding, rule configuration, source IP restrictions, network ACL and internal system firewalls, and note that some platforms need to restart the instance after modification. Mastering these key points can effectively improve

There are three main ways to achieve automatic mount in Linux: First, use /etc/fstab to manually configure the mount point, which is suitable for fixed devices, and you need to edit the fstab file and specify the device with UUID to ensure that the mount point exists; second, use autofs to realize dynamic automatic mount, which is suitable for mounting NFS and other network file systems on demand, and autofs and its sub-configuration files need to be installed and configured; third, for hot-swap devices such as USB flash drives, it is recommended to use udisks2 or select a distribution with a desktop environment to achieve automatic mount.

To use iptables to open the port, first confirm whether it is running. If it is not running, it will be started and set to boot automatically; secondly add rules to the INPUT chain, such as: iptables-AINPUT-ptcp--dport8080-jACCEPT; then save the rules to prevent restart failure, use serviceiptablessave to CentOS/RHEL, install iptables-persistent and save it; finally use iptables-L-n-line-numbers to check whether the rules are effective. Note that if the system uses firewalld or nftables, it needs to use the corresponding work instead.

Diskquotasaresetuptopreventusersfromconsumingexcessivediskspaceonsharedsystems.1.Checkifthefilesystemsupportsquotasbyverifyingmountoptionslikeusrquotaorgrpquota,andmodify/etc/fstabifneeded.2.Enablequotasbyrunningquotachecktoinitializethequotadatabase

In Linux systems, you mainly rely on the df and du commands to view disk space usage. 1. Use df-sh to view the overall disk space usage, focus on the Use% column to determine whether it needs to be cleaned or expanded; 2. Use du-sh/path/to/directory to view the usage of specific directories, and use du-sh/path/to/directory/*|sort-hr to view the subdirectory size sorting; 3. Use find/path/to/search-typef-size 100M to quickly locate large files. It is recommended to start searching from common directories to improve efficiency. Mastering these commands can effectively analyze and manage disk space.

To disable the systemd service, you must first confirm the service status, use the systemctlstatus service name to check whether it is active, and confirm the service name through systemctllist-units--type=service; after confirming that it is correct, 1. Execute the sudosystemctlstop service name to stop the running service; 2. Execute the sudosystemctldisable service name to prohibit the startup; If the service needs to be completely prevented from being called, you can choose step 3: Execute the sudosystemctlmask service name to block it, but unmask first when restoring; pay attention to avoid incorrectly dependent on critical system services such as NetworkM

The key to configuring an NFS client is to confirm that the service is available, correctly install the tools, mount the directory and set up automatic mount. 1. Use showmount-e[server-ip] to check the server shared directory; 2. Install the nfs-utils or nfs-common package; 3. Start and enable the rpcbind service; 4. Use the mount command to mount the NFS shared directory. It is recommended to add -tnfs to clarify the file system type; 5. Add an entry in /etc/fstab to achieve automatic mount on the startup, pay attention to using the _netdev option and nfs4 type (if supported). When troubleshooting problems, focus on checking permissions, service status, network connectivity, and SELinux or AppArmor limits.

htop is an intuitive system monitoring tool that provides real-time CPU and memory usage. 1. After entering htop, the process list is displayed by CPU usage by default. You can use the up and down arrows to select the process, F6 changes the sorting method, and H shows/hide threads; 2. Press F9 or k to end the process, and support sending SIGTERM or SIGKILL signals, but be careful to avoid accidentally killing key processes; 3. Press F3 to enter keywords to search for specific processes, which facilitates quick positioning of service running status; 4. Press F2 to adjust the interface settings, F4 filters the process list, and F7/F8 to adjust priority (requires root permission). Mastering these operations can significantly improve system monitoring efficiency.