Dmesg: Difference between revisions
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dmesg is a fixed-size ringbuffer in linux kernel memory. | dmesg is a fixed-size ringbuffer in linux kernel memory, on the order of hundreds of KByte large. | ||
Revision as of 17:24, 27 February 2024
✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.
dmesg is a fixed-size ringbuffer in linux kernel memory, on the order of hundreds of KByte large.
Both writing (printk()) and reading from dmesg (/dev/kmsg) is effectively privileged thing, so it is not used for general purpose logging.
- (note that your userspace logger might well choose to read out dmesg and write it to its own logs)
Primarily some lower level details from the kernel; things that write to it include
- boot code
- ongoing important evens like
- changes in connected devices
- oom-killer
- segfaults
- device errors
Ringbuffer means that once full, it rewrites old lines.
That fixed size is usually on the order of dozens to hundreds of kilobytes.
If
grep CONFIG_LOG_BUF_SHIFT /boot/config-`uname -r`
says something like
CONFIG_LOG_BUF_SHIFT=18
that means 256KiB (1<<18)
See also: