KMSG

kmsg refers to the Linux kernel message facility, and the /dev/kmsg character device that provides a stream of kernel log messages to userspace. The kernel collects messages generated by printk at various priorities into a circular log buffer. The /dev/kmsg interface exposes those messages to user-space processes in real time, allowing monitoring tools to receive new kernel messages as they occur, without waiting for a periodic dump.

Usage: Reading from /dev/kmsg is typically limited to processes with appropriate privileges (for example, CAP_SYSLOG or root). It complements the traditional dmesg and /proc/kmsg interfaces and is commonly used by system logging daemons such as systemd-journald to capture kernel logs for storage and analysis.

Implementation and scope: The kmsg interface is implemented in the kernel's printk subsystem; the device file is created by the kernel and is part of the Linux kernel logging facilities. Messages include a timestamp and log level as defined by the kernel's printk facility, using the standard KERN_* prefixes.

Limitations and security: The log buffer is finite and may wrap, with older messages overwritten. Access to /dev/kmsg can expose sensitive kernel details; permission controls apply.

See also: dmesg, /proc/kmsg, printk, kernel log levels, journald, rsyslog.