dmesg命令来自英文词组“display message”的缩写，其功能是用于显示开机过程信息。Linux系统内核会将开机过程信息存储在环形缓冲区（ring buffer）中，随后再写入到/var/log/dmesg文件里，如果开机时来不及查看这些信息，则可以利用dmesg命令进行调取。
语法格式：dmesg [参数]
常用参数：
| -c | 清空环形缓冲区中的内容 |
| -d | 显示信息时间差 |
| -D | 禁止向终端输出信息 |
| -E | 启用向终端输出信息 |
| -H | 以更易读的格式输出信息 |
| -k | 显示内核信息 |
| -l | 设置输出级别 |
| -L | 显示彩色信息 |
| -n | 设置记录信息的层级 |
| -r | 显示原生消息缓冲区信息 |
| -s | 设置环形缓冲区的大小 |
| -t | 不显示消息时间戳 |
| -T | 显示易读的时间戳格式 |
| -u | 显示用户空间消息 |
| -w | 等待新消息 |
| --help | 显示帮助信息 |
| --version | 显示版本信息 |
参考示例
显示全部的系统开机过程信息：
[root@linuxcool ~]# dmesg
显示与指定硬盘设备相关的开机过程信息：
[root@linuxcool ~]# dmesg | grep sda [ 5.065202] sd 2:0:0:0: [sda] 41943040 512-byte logical blocks: (21.5 GB/20.0 GiB) [ 5.065253] sd 2:0:0:0: [sda] Write Protect is off [ 5.065255] sd 2:0:0:0: [sda] Mode Sense: 00 3a 00 00 [ 5.065396] sd 2:0:0:0: [sda] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA [ 5.069757] sda: sda1 sda2 [ 5.083650] sd 2:0:0:0: [sda] Attached SCSI disk [ 8.379578] XFS (sda1): Mounting V5 Filesystem [ 9.009002] XFS (sda1): Ending clean mount
显示与内存相关的开机过程信息：
[root@linuxcool ~]# dmesg | grep memory [ 0.000000] Base memory trampoline at [(____ptrval____)] 98000 size 24576 [ 0.000000] Early memory node ranges [ 0.000000] PM: Registered nosave memory: [mem 0x00000000-0x00000fff] [ 0.000000] PM: Registered nosave memory: [mem 0x0009e000-0x0009efff] [ 0.000000] PM: Registered nosave memory: [mem 0x0009f000-0x0009ffff] [ 0.000000] PM: Registered nosave memory: [mem 0x000a0000-0x000dbfff] [ 0.000000] PM: Registered nosave memory: [mem 0x000dc000-0x000fffff] [ 0.000000] PM: Registered nosave memory: [mem 0x7fee0000-0x7fefefff] [ 0.000000] PM: Registered nosave memory: [mem 0x7feff000-0x7fefffff] [ 0.033593] Freeing SMP alternatives memory: 32K [ 1.716349] Freeing initrd memory: 26068K [ 1.893488] Non-volatile memory driver v1.3 [ 2.374146] Freeing unused kernel memory: 2348K [ 2.382073] Freeing unused kernel memory: 2020K [ 2.382772] Freeing unused kernel memory: 280K [ 4.604351] [drm] Max dedicated hypervisor surface memory is 0 kiB [ 4.604352] [drm] Maximum display memory size is 262144 kiB [ 4.606362] [TTM] Zone kernel: Available graphics memory: 1006652 kiB
清空环形缓冲区中的已有日志内容：
[root@linuxcool ~]# dmesg -c