Linux – How to write to dmesg from command line

command linedmesgkernellinuxlogs

I'd like to write a statement to dmesg. How can I do this?

Best Answer

Write to /dev/kmsg (not /proc/kmsg as suggested by @Nils). See linux/kernel/printk/printk.c devkmsg_writev for the kernel-side implementation and systemd/src/journal/journald-kmsg.c server_forward_kmsg for an example of usage.

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Linux – How to dmesg content be logged into a file

You need to look at either /etc/rsyslog.conf or /etc/syslog.conf. If you have a line early on such as:

*.*                -/var/log/syslog

Everything, including the stuff from dmesg, should go to that file. To target it better:

kernel.*           -/var/log/dmesg

If that fails for some reason, you could periodically (e.g. via cron):

dmesg > /var/log/dmesg

Depending on how big the dmesg buffer is (this is compiled into the kernel, or set via the log_buf_len parameter) and how long your system has been up, that will keep a record of the kernel log since it started.

If you want to write the dmesg output continuously to a file use the -w (--follow) flag.

dmesg --follow > mydmesg.log

linux command-line logs dmesg – How to See dmesg Output as It Changes

Relatively recent dmesg versions provide a follow option (-w, --follow) which works analogously to tail -f.

Thus, just use following command:

$ dmesg -wH

(-H, --human enables user-friendly features like colors, relative time)

Those options are available for example in Fedora 19.

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Linux – How to dmesg content be logged into a file

linux command-line logs dmesg – How to See dmesg Output as It Changes

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