dmesg

kernel ring buffer message viewer

TLDR

Show kernel messages

$ sudo dmesg

Show kernel error messages

$ sudo dmesg -l err

Follow kernel messages in real-time

$ sudo dmesg -w

Show messages with human-readable timestamps

$ sudo dmesg -T

Show messages in human-readable form

$ sudo dmesg -H

Colorize output

$ sudo dmesg -L

Filter messages by facility

$ sudo dmesg -f kern

SYNOPSIS

dmesg [-l level] [-f facility] [-T] [-H] [-w] [-L]

dmesg prints and controls the kernel ring buffer, which contains messages from the kernel including hardware detection, driver loading, and system events. It is essential for debugging hardware and driver issues.

PARAMETERS

-l, --level level

Restrict output to specified log levels (emerg, alert, crit, err, warn, notice, info, debug)

-f, --facility facility

Restrict output to specified facilities (kern, user, mail, daemon, etc.)

-T, --ctime

Print human-readable timestamps

-H, --human

Enable human-readable output with colors and timestamps

-w, --follow

Wait for new messages (like tail -f)

-L, --color

Colorize output

-c, --read-clear

Clear the ring buffer after printing

-C, --clear

Clear the ring buffer without printing

-n, --console-level level

Set level of messages printed to console

-k, --kernel

Print kernel messages only

-u, --userspace

Print userspace messages only

--time-format format

Timestamp format: ctime, reltime, delta, iso, raw

--since time

Display records since the specified time

--until time

Display records until the specified time

-J, --json

Output in JSON format

-t, --notime

Do not print kernel timestamps

-r, --raw

Print raw message buffer with log-level prefixes

-x, --decode

Decode facility and level to human-readable prefixes

INSTALL

sudo apt install util-linux

sudo dnf install util-linux

sudo pacman -S util-linux

sudo apk add dmesg

sudo zypper install util-linux

brew install util-linux

nix profile install nixpkgs#util-linux

CAVEATS

Requires root privileges on most systems. The -w (follow) option requires kernel 3.5.0+ (for /dev/kmsg). The -T and -H options are util-linux userspace features and do not require a specific kernel version.

HISTORY

Part of util-linux package. The kernel ring buffer has been part of Linux since early versions, providing essential diagnostic information.