systemd Developer Lennart Poettering lennart@poettering.net sysctl.d 5 sysctl.d Configure kernel parameters at boot /etc/sysctl.d/*.conf /run/sysctl.d/*.conf /usr/lib/sysctl.d/*.conf At boot, systemd-sysctl.service8 reads configuration files from the above directories to configure sysctl8 kernel parameters. The configuration files contain a list of variable assignments, separated by newlines. Empty lines and lines whose first non-whitespace character is # or ; are ignored. Note that either / or . may be used as separators within sysctl variable names. If the first separator is a slash, remaining slashes and dots are left intact. If the first separator is a dot, dots and slashes are interchanged. kernel.domainname=foo and kernel/domainname=foo are equivalent and will cause foo to be written to /proc/sys/kernel/domainname. Either net.ipv4.conf.enp3s0/200.forwarding or net/ipv4/conf/enp3s0.200/forwarding may be used to refer to /proc/sys/net/ipv4/conf/enp3s0.200/forwarding. 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. The settings configured with sysctl.d files will be applied early on boot. The network interface-specific options will also be applied individually for each network interface as it shows up in the system. (More specifically, net.ipv4.conf.*, net.ipv6.conf.*, net.ipv4.neigh.* and net.ipv6.neigh.*) # Set kernel YP domain name kernel.domainname=example.com systemd1, systemd-sysctl.service8, systemd-delta1, sysctl8, sysctl.conf5