Recently, an unanswered Linux operation and maintenance interview question was circulated on the Internet. 51CTO blogger Hao Jiu took advantage of his spare time and used his three-year operation and maintenance experience to hand in an answer sheet. Welcome everyone to comment together~
(Hao Jiu is not familiar with iptables, please add it to netizens here, and specific problems need to be analyzed in detail) 
MySQL related questions How to improve the security level of MYSQL after the new installation of MYSQL A. Modify the default MySQL port B. Under linux, you can use iptables to restrict access to the IP address of the MySQL port C. Set more complex passwords for all users and specify the corresponding account strictly Access IP (you can specify the user's accessible IP address in the user table of the mysql library) D. Root privileged account processing (it is recommended to set a strong password for the root account and specify that only local login is allowed) E. Turn on the binary query log and Slow query log F. mysql installation directory and data storage directory permission control: give mysql installation directory read permission, give mysql log and data directory read and write permission G. Delete useless mysql account and delete useless database (installed The mysql default will have a test library, which can be deleted)
The master-slave principle of MYSQL, how to configure the file as a whole, replication has 3 steps: A.master records the changes to the binary log (these records are called binary log events); B.slave will The master's binary log events are copied to its relay log; C.slave redo events in the relay log, and it will change its own data. 
(1) The IO thread on the Slave connects to the Master and requests the log content from the specified location of the specified log file (or the log from the very beginning); (2) After the Master receives the request from the IO thread of the Slave, it passes The IO thread responsible for replication reads the log information after the specified location of the specified log according to the request information, and returns it to the IO thread on the Slave side. In addition to the information contained in the log, the returned information also includes the name of the binary log file on the Master side and the location in the Binary log of the returned information; (3) After the IO thread of the Slave receives the information, it will receive it The log content is written to the end of the RelayLog file (mysql-relay-lin.xxxxx) on the Slave side in turn, and the file name and location of the bin-log on the Master side read are recorded in the master-info file for the next time When reading, it can clearly tell the master "I need to start the log content from a certain bin-log, please send it to me" (4) After the SQL thread of the Slave detects the new content in the Relay Log , It will immediately parse the content of the Log file into those executable queries or operation statements when it is actually executed on the Master side, and execute those queries or operation statements on its own. In this way, it is actually executed on the master side and the slave side. The same query or operation statement, so the data at both ends are exactly the same. Supplement: Advantages of mysql master-slave replication "1" If there is a problem with the master server, you can quickly switch to the service provided by the slave server; "2" You can perform query operations on the slave server to reduce the access pressure of the master server; "3" Yes Perform the backup on the slave server to avoid affecting the services of the master server during the backup. mysql" grant select, insert, update, delete on book.* to test2@localhost identified by'abc'; #Increase test2 user, password is abc. You can only log in on the host localhost, and you can only access tables in the book library, with query, insert, update, and delete permissions; syntax: mysql" GRANT "permissions" ON "library". "Table" TO'user'@'host name' identified by'password'; 
(The subject is an unprofessional MCSE, remember that in win2003, there is the concept of release assignment, please add it to netizens) In a domain environment, one server should be used as the update server of the domain control patch, using "release and The function of "assignment", batch update the patch to other servers in the intranet; 
Batch processing + scheduled task + ftp upload to remote server 
Use ISA firewall? 
Audible and visual alarm is set up to meet customers' special requirements for alarm loudness and installation location. At the same time, two alarm signals, sound and light, are issued. Special fields: iron and steel metallurgy, telecommunication towers, hoisting machinery, construction machinery, ports, transportation, wind power generation, ocean-going ships and other industries; it is an accessory product in the industrial alarm system.
emergency alarm,Audible Visual Signals,Visual Alarm devices,sound and light siren,visual alarm system
Taixing Minsheng Electronic Co.,Ltd. , https://www.ms-speakers.com