dmesg命令对于设备故障的诊断是非常重要的。在dmesg命令的帮助下进行硬件的连接或断开连接操作时，我们可以看到硬件的检测或者断开连接的信息。dmesg命令在多数基于Linux和Unix的操作系统中都可以使用。
下面我们展示一些最负盛名的dmesg命令工具以及其实际使用举例。
dmesg命令的使用语法如下。
# dmesg [options...]
1. 列出加载到内核中的所有驱动
我们可以使用如‘more’。 ‘tail’, ‘less ’或者‘grep’文字处理工具来处理‘dmesg’命令的输出。由于dmesg日志的输出不适合在一页中完全显示，因此我们使用管道（pipe）将其输出送到more或者less命令单页显示。
linuxidc@linuxidc:~/linuxidc.com$ dmesg | more
[ 0.000000] Linux version 4.18.0-17-generic (buildd@lgw01-amd64-021) (gcc ver
sion 7.3.0 (Ubuntu 7.3.0-16ubuntu3)) #18~18.04.1-Ubuntu SMP Fri Mar 15 15:27:12
UTC 2019 (Ubuntu 4.18.0-17.18~18.04.1-generic 4.18.20)
[ 0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.18.0-17-generic root=UUI
D=21f64724-a9be-43a7-8e83-2e7ffd1ba2a3 ro quiet splash
[ 0.000000] KERNEL supported cpus:
[ 0.000000] Intel GenuineIntel
[ 0.000000] AMD AuthenticAMD
[ 0.000000] Centaur CentaurHauls
[ 0.000000] Disabled fast string operations
[ 0.000000] x86/fpu: Supporting XSAVE feature 0x001: 'x87 floating point regi
sters'
[ 0.000000] x86/fpu: Supporting XSAVE feature 0x002: 'SSE registers'
[ 0.000000] x86/fpu: Supporting XSAVE feature 0x004: 'AVX registers'
[ 0.000000] x86/fpu: xstate_offset[2]: 576, xstate_sizes[2]: 256
[ 0.000000] x86/fpu: Enabled xstate features 0x7, context size is 832 bytes,
using 'standard' format.
[ 0.000000] BIOS-provided physical RAM map:
[ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009e7ff] usable
[ 0.000000] BIOS-e820: [mem 0x000000000009e800-0x000000000009ffff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000000dc000-0x00000000000fffff] reserved
[ 0.000000] BIOS-e820: [mem 0x0000000000100000-0x00000000bfecffff] usable
[ 0.000000] BIOS-e820: [mem 0x00000000bfed0000-0x00000000bfefefff] ACPI data
--更多--
linuxidc@linuxidc:~/linuxidc.com$ dmesg | less
2. 列出所有被检测到的硬件
要显示所有被内核检测到的硬盘设备，你可以使用‘grep’命令搜索‘sda’关键词，如下：
linuxidc@linuxidc:~/linuxidc.com$ dmesg | grep sda
[ 3.323824] sd 26:0:0:0: [sda] 125829120 512-byte logical blocks: (64.4 GB/60.0 GiB)
[ 3.323848] sd 26:0:0:0: [sda] Write Protect is off
[ 3.323850] sd 26:0:0:0: [sda] Mode Sense: 61 00 00 00
[ 3.323886] sd 26:0:0:0: [sda] Cache data unavailable
[ 3.323887] sd 26:0:0:0: [sda] Assuming drive cache: write through
[ 3.325104] sda: sda1
[ 3.325583] sd 26:0:0:0: [sda] Attached SCSI disk
[ 3.690525] EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null)
[ 4.265965] EXT4-fs (sda1): re-mounted. Opts: errors=remount-ro
注解 ‘sda’表示第一块 SATA硬盘，‘sdb’表示第二块SATA硬盘。若想查看IDE硬盘搜索‘hda’或‘hdb’关键词。
3. 只输出dmesg命令的前20行日志
在‘dmesg’命令后跟随‘head’命令来显示开始几行，‘dmesg | head -20′命令将显示开始的前20行。
[ 0.000000] AMD AuthenticAMD
[ 0.000000] Centaur CentaurHauls
[ 0.000000] Disabled fast string operations
[ 0.000000] x86/fpu: Supporting XSAVE feature 0x001: 'x87 floating point registers'
[ 0.000000] x86/fpu: Supporting XSAVE feature 0x002: 'SSE registers'
[ 0.000000] x86/fpu: Supporting XSAVE feature 0x004: 'AVX registers'
[ 0.000000] x86/fpu: xstate_offset[2]: 576, xstate_sizes[2]: 256
[ 0.000000] x86/fpu: Enabled xstate features 0x7, context size is 832 bytes, using 'standard' format.
[ 0.000000] BIOS-provided physical RAM map:
[ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009e7ff] usable
[ 0.000000] BIOS-e820: [mem 0x000000000009e800-0x000000000009ffff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000000dc000-0x00000000000fffff] reserved
[ 0.000000] BIOS-e820: [mem 0x0000000000100000-0x00000000bfecffff] usable
[ 0.000000] BIOS-e820: [mem 0x00000000bfed0000-0x00000000bfefefff] ACPI data
[ 0.000000] BIOS-e820: [mem 0x00000000bfeff000-0x00000000bfefffff] ACPI NVS
[ 0.000000] BIOS-e820: [mem 0x00000000bff00000-0x00000000bfffffff] usable
4. 只输出dmesg命令最后20行日志