有时Linux系统或者系统上运行的mysqld或者其它进程，会发生一些莫名其妙的问题，比如突然挂掉了，比如突然重启等等。在软件上找不到问题所在，此时我们应该怀疑硬件或者内核的问题，此时我们就可以使用 dmesg 来查看：

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)

直接执行：dmesg 或者 dmesg > dmg.txt 就可以获得硬件信息和内核启动时的信息。