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linux-command/command/dmesg.md

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1dmesg
2===
3
4显示Linux系统启动信息
5
6## 补充说明
7
8**dmesg命令** 被用于检查和控制内核的环形缓冲区。kernel会将开机信息存储在ring buffer中。您若是开机时来不及查看信息，可利用dmesg来查看。开机信息保存在`/var/log/dmesg`文件里。
9
10###  语法 
11
12```shell
13dmesg(选项)
14```
15
16###  选项 
17
18```shell
19-c：显示信息后，清除ring buffer中的内容；
20-s<缓冲区大小>：预设置为8196，刚好等于ring buffer的大小；
21-n：设置记录信息的层级。
22```
23
24###  实例 
25
26```shell
27[root@localhost ~]# dmesg | head
28Linux version 2.6.18-348.6.1.el5 (mockbuild@builder17.centos.org) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-54)) #1 SMP Tue May 21 15:34:22 EDT 2013
29BIOS-provided physical RAM map:
30 BIOS-e820: 0000000000010000 - 000000000009f400 (usable)
31 BIOS-e820: 000000000009f400 - 00000000000a0000 (reserved)
32 BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved)
33 BIOS-e820: 0000000000100000 - 000000007f590000 (usable)
34 BIOS-e820: 000000007f590000 - 000000007f5e3000 (ACPI NVS)
35 BIOS-e820: 000000007f5e3000 - 000000007f5f0000 (ACPI data)
36 BIOS-e820: 000000007f5f0000 - 000000007f600000 (reserved)
37 BIOS-e820: 00000000e0000000 - 00000000e8000000 (reserved)
38```
39
40查看硬盘基础信息
41
42```shell
43dmesg | grep sda
44
45[    2.442555] sd 0:0:0:0: [sda] 488281250 512-byte logical blocks: (250 GB/232 GiB)
46[    2.442590] sd 0:0:0:0: [sda] Write Protect is off
47[    2.442592] sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
48[    2.442607] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
49[    2.447533]  sda: sda1
50[    2.448503] sd 0:0:0:0: [sda] Attached SCSI disk
51```
52
53查看多关键字
54
55```shell
56dmesg | grep -E "vcc5v0_host|vcc_3v3_s0|ttyS"
57
58[    1.193143] vcc5v0_host: supplied by vcc5v0_usb
59[    1.481139] feb80000.serial: ttyS5 at MMIO 0xfeb80000 (irq = 73, base_baud = 1500000) is a 16550A
60[    1.513541] vcc_3v3_s0: supplied by vcc5v0_sys
61```

1	`dmesg`
2	`===`
3
4	`显示Linux系统启动信息`
5
6	`## 补充说明`
7
8	dmesg命令被用于检查和控制内核的环形缓冲区。kernel会将开机信息存储在ring buffer中。您若是开机时来不及查看信息，可利用dmesg来查看。开机信息保存在`/var/log/dmesg`文件里。
9
10	`### 语法`
11
12	```shell
13	`dmesg(选项)`
14	```
15
16	`### 选项`
17
18	```shell
19	`-c：显示信息后，清除ring buffer中的内容；`
20	`-s<缓冲区大小>：预设置为8196，刚好等于ring buffer的大小；`
21	`-n：设置记录信息的层级。`
22	```
23
24	`### 实例`
25
26	```shell
27	`[root@localhost ~]# dmesg \| head`
28	`Linux version 2.6.18-348.6.1.el5 (mockbuild@builder17.centos.org) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-54)) #1 SMP Tue May 21 15:34:22 EDT 2013`
29	`BIOS-provided physical RAM map:`
30	`BIOS-e820: 0000000000010000 - 000000000009f400 (usable)`
31	`BIOS-e820: 000000000009f400 - 00000000000a0000 (reserved)`
32	`BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved)`
33	`BIOS-e820: 0000000000100000 - 000000007f590000 (usable)`
34	`BIOS-e820: 000000007f590000 - 000000007f5e3000 (ACPI NVS)`
35	`BIOS-e820: 000000007f5e3000 - 000000007f5f0000 (ACPI data)`
36	`BIOS-e820: 000000007f5f0000 - 000000007f600000 (reserved)`
37	`BIOS-e820: 00000000e0000000 - 00000000e8000000 (reserved)`
38	```
39
40	`查看硬盘基础信息`
41
42	```shell
43	`dmesg \| grep sda`
44
45	`[ 2.442555] sd 0:0:0:0: [sda] 488281250 512-byte logical blocks: (250 GB/232 GiB)`
46	`[ 2.442590] sd 0:0:0:0: [sda] Write Protect is off`
47	`[ 2.442592] sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00`
48	`[ 2.442607] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA`
49	`[ 2.447533] sda: sda1`
50	`[ 2.448503] sd 0:0:0:0: [sda] Attached SCSI disk`
51	```
52
53	`查看多关键字`
54
55	```shell
56	`dmesg \| grep -E "vcc5v0_host\|vcc_3v3_s0\|ttyS"`
57
58	`[ 1.193143] vcc5v0_host: supplied by vcc5v0_usb`
59	`[ 1.481139] feb80000.serial: ttyS5 at MMIO 0xfeb80000 (irq = 73, base_baud = 1500000) is a 16550A`
60	`[ 1.513541] vcc_3v3_s0: supplied by vcc5v0_sys`
61	```