What are the common problems with the SSH protocol? Full summary of solutions

in the remote server management and operation and maintenance scenario, SSH protocol is the core tool to ensure data transmission security and realize remote control. However, in actual use, many users will encounter various problems such as connection failure, limited authority, security alarms, etc., which affect work efficiency and even server security. This article will sort out the high-frequency problems in the use of SSH protocol, and disassemble them one by one in combination with practical operation schemes to help users at different levels quickly locate and solve faults, and improve the stability and security of remote operation.

, SSH protocol connection failure how to check?

connection failure is the most common problem in the use of SSH protocol, involving network, configuration, service status and other factors, need to be checked step by step according to the process.

1, check network and service status

first need to confirm the network connectivity of the local device and the target server, you can test whether the server IP is reachable through the ping command; then check whether the server-side SSH protocol service is running normally, Linux the system can execute the systemctl status sshd command to view the service status, If the service is not started, execute the systemctl start sshd command to start, and set the boot self-start to avoid subsequent failures.

2 Verify configuration and port restrictions

If the service is still unable to connect normally, you need to check the SSH protocol configuration file/etc/ssh/sshd_config to confirm whether the port number, the user allowed to log in, and the password Orthrus are correct; at the same time, check the server firewall and cloud platform security group to ensure that the SSH protocol defaults to 22 ports or custom ports are open to avoid connection failure due to port interception.

2, SSH protocol authority is limited how to solve

permission restrictions often cause users to log in, execute commands or transfer files, which need to be solved from two aspects: user permissions and file permissions.

1, user Orthrus abnormal

If the specified user cannot log in through the SSH protocol, first check the AllowUsers or DenyUsers parameter in the sshd_config file to confirm whether the target user is in the allowed login list; at the same time verify whether the user password has expired, reset the password through the passwd command, or check the user's home directory permissions to ensure that the permissions are not set to 777 and other high permissions to avoid SSH protocol from refusing to log in due to security policies.

2, the file operation authority is insufficient

can not perform file operations after successful login, you need to check the permissions of the target file or directory settings, you can adjust the permissions level through the chmod command, such as giving execution permissions chmod + x filename; if it involves system-level files, you can upgrade permissions through the sudo command, while ensuring that the current user has the appropriate permissions in the sudoers configuration file to avoid failure due to insufficient permissions.

How to deal with the SSH protocol security alarm?

with the upgrade of network attack methods, SSH protocol is facing security risks such as brute force cracking and key leakage, and all kinds of alarms need to be dealt with in time to ensure server security.

1, brute force attack alarm

If a large number of SSH protocol login failure records appear in the log, indicating that the server is suffering from brute force cracking attacks, it is necessary to immediately modify the SSH protocol default port 22 as a custom port, disable the password login method and use the key login; at the same time install fail2ban and other protection tools, set the login failure threshold, automatically intercept malicious Internet Protocol Address, reduce the risk of attack.

2, key file permissions are too high alarm

permission alarm occurs when using the key to log in, you need to check the permissions of the local private key file and the server-side public key file. The permissions of the private key file need to be set to 600, and the permissions of the public key file are set to 644 to avoid SSH protocol due to excessive permissions. Determine that there is a security risk of the key and reject the key login request.

How to optimize the SSH protocol connection card?

some users will encounter high SSH protocol connection delay, operation card problems, mostly related to the network environment, configuration parameters, can be optimized by targeted settings.

1, adjust the network configuration

if the SSH protocol connection card is caused by network fluctuations, the TCPKeepAlive parameter can be enabled in the sshd_config file and set to TCPKeepAlive yes to keep the TCP connection active; at the same time, adjust the ClientAliveInterval and ClientAliveCountMax parameters to shorten the heartbeat detection interval, and timely identify and restore abnormal connections.

2, turn off unnecessary service functions

SSH protocol enabled by default will take up additional resources, can turn off the DNS reverse resolution function, set UseDNS no, reduce the server DNS query time; at the same time disable GSSAPI authentication, set GSSAPIAuthentication no, to avoid connection delays due to complex authentication process, improve the response speed of SSH protocol connections.

To sum up, the common problems of the SSH protocol cover the four core dimensions of connection, authority, security and performance, and each problem corresponds to a clear troubleshooting and solution process. By step-by-step troubleshooting of network and service status, adjusting configuration and permissions, strengthening security protection, and optimizing performance parameters, various faults in the use of the SSH protocol can be effectively solved, and the stability and security of remote operation can be guaranteed. In daily use, it is also necessary to regularly check the configuration and service status of the SSH protocol to avoid latent risks in advance and improve the efficiency and reliability of remote operation and maintenance.