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1. Set the root password and use the SU command In the default Ubuntu configuration, the root user is disabled because no password is set. By setting a password for the root user, the traditional [su] command can be used for transitions 3. Make the locate command available The find command is often used to search for a specific file on the whole Linux system, but find is somewhat confusing in its options. The locate command is capable of extracting all files with a given filename.

1. Introduction of Clamav anti-virus software 1.1 Install # apt install clamav clamav-daemon Clamav-related configuration files are installed in the /etc/clamav/ folder 1.2 Update your virus definitions # freshclam The above command will update the virus definitions, but if you get the following error, change the log settings and run it again ERROR: /var/log/clamav/freshclam.log is locked by another process ERROR: Problem with internal logger (UpdateLogFile = /var/log/clamav/freshclam.log) ⚫The default settings are prone to log-related errors during freshclam (virus definition update). Therefore, once you have deleted the log file and changed the logrotate settings

Instructions on how to get a certificate and apply it to apache, mail server, FTP server and convert to SSL with Let's Encrypt. 1. Get a certificate(Let's Encrypt) 1.1 Advance preparation ①Enable mod_ssl # a2enmod ssl ②Install a client tool to obtain a Let's Encrypt certificate # apt -y install certbot ③Obtaining a Let's Encrypt certificate It is assumed that a web server such as Apache or Nginx is running. If the web server is not running on the server where the work is to be carried out, follow step ④. It is also assumed that the server on which the work is to be carried out (the server with the FQDN for which you want to obtain the certificate) is accessible from the Internet via port 80.

1. system backup 1.1 Backup of /var/www/html 1.2 Mysql database backup 2. system restore 2.1 Restore the backup files under HTML 1) Store the HTML backup files used for backup in the "/ (root)" directory. 1) Create db_backup.sh script under /var/www/system. 2.2 Restore MySQL database 1) Save the DB backup file to any directory and unzip the data.