有時Linux系統或者系統上運行的mysqld或者其它進程，會發生一些莫名其妙的問題，比如突然掛掉了，比如突然重啟等等。在軟件上找不到問題所在，此時我們應該懷疑硬件或者內核的問題，此時我們就可以使用 dmesg 來查看：
NAME
dmesg - print or control the kernel ring buffer
SYNOPSIS
dmesg [-c] [-r] [-n level] [-s bufsize]
DESCRIPTION
dmesg is used to examine or control the kernel ring buffer.
The program helps users to print out their bootup messages. Instead of copying the messages by hand, the user need
only:
dmesg > boot.messages
and mail the boot.messages file to whoever can debug their problem.
OPTIONS
-c Clear the ring buffer contents after printing.
-r Print the raw message buffer, i.e., don’t strip the log level prefixes.
-s bufsize
Use a buffer of size bufsize to query the kernel ring buffer. This is 16392 by default. (The default kernel
syslog buffer size was 4096 at first, 8192 since 1.3.54, 16384 since 2.1.113.) If you have set the kernel
buffer to be larger than the default then this option can be used to view the entire buffer.
-n level
Set the level at which logging of messages is done to the console. For example, -n 1 prevents all messages,
except panic messages, from appearing on the console. All levels of messages are still written to /proc/kmsg,
so syslogd(8) can still be used to control exactly where kernel messages appear. When the -n option is used,
dmesg will not print or clear the kernel ring buffer.
When both options are used, only the last option on the command line will have an effect.
SEE ALSO
syslogd(8)
直接執行：dmesg 或者 dmesg > dmg.txt 就可以獲得硬件信息和內核啟動時的信息。
