Kernel Module Configuration
Kernel module i2c-dev must be loaded. On some distributions, it is built into the Linux kernel. If not, it must be loaded explicitly.
To see if i2c-dev is built into the kernel, issue the following command:
grep i2c-dev.ko /lib/modules/`uname -r`/modules.builtin
If i2c-dev is not built in, add the line "i2c_dev" to /etc/modules or a file containing the single line:
to directory /etc/modules-load.d
From the freedesktop.org systemd doc:
systemd-modules-load.service(8) reads files from the [following]directories which contain kernel modules to load during boot in a static list.
Each configuration file is named in the style of /etc/modules-load.d/program.conf.