/etc/sysctl.d/*.conf /run/sysctl.d/*.conf /usr/lib/sysctl.d/*.conf
Configure kernel parameters at boot，均用来在系统启动时配置内核参数
At boot, systemd-sysctl.service(8) reads configuration files from the above directories to configure sysctl(8) kernel parameters.
Each configuration file shall be named in the style of program.conf. Files in /etc/ override files with the same name in /usr/lib/ and /run/. Files in /run/ override files with the same name in /usr/lib/. Packages should install their configuration files in /usr/lib/. Files in /etc/ are reserved for the local administrator, who may use this logic to override the configuration files installed by vendor packages. All configuration files are sorted by their filename in lexicographic order, regardless of which of the directories they reside in. If multiple files specify the same variable name, the entry in the file with the lexicographically latest name will be applied. It is recommended to prefix all filenames with a two-digit number and a dash, to simplify the ordering of the files. If the administrator wants to disable a configuration file supplied by the vendor, the recommended way is to place a symlink to /dev/null in /etc/sysctl.d/ bearing the same filename.