Dmesg

dmesg is a command-line utility that reads and prints messages from the kernel's ring buffer. The kernel writes messages about boot progress, hardware events, driver status, and other internal notices to this buffer, which is preserved in memory for a limited time while the system is running.

The kernel ring buffer acts as a circular store for diagnostic messages. As new messages arrive, older ones may be overwritten when space is needed. dmesg provides a snapshot of recent kernel activity, useful for troubleshooting hardware, loading modules, and diagnosing boot problems.

Typical usage includes printing the current content and performing simple filtering. Options commonly used are -c to clear the buffer after printing, -T to convert timestamps to a human-readable format, -n level to control what messages show on the console, and -s bytes to adjust the amount of data read from the buffer. Users can redirect output or pipe it to commands like grep.

On many systems access to dmesg is restricted to privileged users or to those with the CAP_SYSLOG capability. Some systems implement a dmesg_restrict setting to limit who can view kernel messages. For privacy and security, consider the exposure of sensitive hardware or driver information in logs.

See also: syslog, kernel log, system log management, and the journal in systems using the systemd journal.