file: /proc/sys/kernel/printk_devkmsg
variable: kernel.printk_devkmsg
Official reference

Control the logging to /dev/kmsg from userspace:

ratelimit: default, ratelimited on: unlimited logging to /dev/kmsg from userspace off: logging to /dev/kmsg disabled

The kernel command line parameter printk.devkmsg= overrides this and is a one-time setting until next reboot: once set, it cannot be changed by this sysctl interface anymore.