dmesg命令

古城微笑少年丶 2022-09-23 11:00 134阅读 0赞

**功能说明：**显示开机信息。  
  
**语　　法：**d[mesg][] \[-cn\]\[-s <缓冲区大小>\]  
  
**补充说明：**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。开机信息亦保存在/var/log目录中，名称为dmesg的文件里。  
  
**参　　数：**  
　-c 　显示信息后，清除ring buffer中的内容。   
　-s<缓冲区大小> 　预设置为8196，刚好等于ring buffer的大小。   
　-n 　设置记录信息的层级。

**扩展阅读一:dmesg[命令][Link 1]主要用途**

主要应用：

dmesg用来显示内核环缓冲区（kernel-ring buffer）内容，内核将各种消息存放在这里。在系统引导时，内核将与硬件和模块初始化相关的信息填到这个缓冲区中。内核环缓冲区中的消息对于诊断系统问题 通常非常有用。在运行dmesg时，它显示大量信息。通常通过[less][]或[grep][]使用管道查看dmesg的输出，这样可以更容易找到待查信息。例如，如果发现硬盘性能低下，可以使用dmesg来检查它们是否运行在DMA模式：

$dmesg | grep DMA  
...  
[id][]e0: BM-DMA at 0xf000-0xf007, BIOS [set][]tings: hda:DMA, hdb:DMA  
ide1: BM-DMA at 0xf008-0xf00f, BIOS settings: hdc:DMA, h[dd][]:DMA  
...

上面几行可以说明每个IDE设备正在什么模式下运行。如果以太网连接出现问题，那么可以在dmesg日志中搜索eth：

$dmesg | grep eth  
forcedeth.c: Reverse Engineered nForce  
ethernet driver. Version 0.49.  
eth0: forcedeth.c: [su][]bsystem: 0147b:1c00  
bound to 0000:00:04.0  
eth0: no IPv6 routers present

如果一切正常，那么dmesg显示每个网卡的硬件配置信息。如果某项系统服务未能得到正确的配置，dmesg日志很快就填满错误消息，这是诊断故障的良好起点。

还可以用来探测系统内核模块的加载情况，比如要检测ACPI的加载情况，使用dmesg | grep a[cp][]i

dmesg |[egrep][] -i ''(apm|acpi)''

Kernel command line: vga=274 quiet console=ttyS3,9600acpi=no-idleoot=/dev/hda3

ACPI: Core Subsystem version \[20010208\]

ACPI: Subsystem [enable][]d

ACPI: System fi[rm][]ware supports: C2

ACPI: plvl2lat=99 plvl3lat=1001

ACPI: C2 enter=1417 C2 [ex][]it=354

ACPI: C3 enter=-1 C3 exit=-1

ACPI: Not using ACPI idle

ACPI: System firmware supports: S0 S1 S4 S5

**扩展阅读二：dmesg命令使用示例**

## 使用示例 ##

### 示例一 将开机信息发邮件 ###

man dmesg 写道

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  [who][]ever can debug their problem.

\[root@new55 ~\]\# dmesg >boot.messages

\[root@new55 ~\]\# [ls][] -l boot.messages   
\-rw-r--r-- 1 root root 15838 12-09 12 begin\_of\_the\_skype\_highlighting 15838 12-09 12 免费  end\_of\_the\_skype\_highlighting:55 boot.messages

\[root@new55 ~\]\# mail -s "Boot Log of Linux Server" public@web3q.net <boot.messages   
\[root@new55 ~\]\#

### 示例二 浏览dmesg输出的信息 ###

\[root@new55 ~\]\# [uname][] -a  
Linux new55 2.6.18-194.el5 \#1 SMP Tue Mar 16 21:52:43 EDT 2010 i686 i686 i386 GNU/Linux

\[root@new55 ~\]\# dmesg | less  
Linux version 2.6.18-194.el5 (mockbuild@x86-007.build.bos.redhat.com) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)) \#1 SMP Tue Mar 16 21:52:43 EDT 2010  
BIOS-provided physical RAM map:  
 BIOS-e820: 0000000000010000 - 000000000009fc00 (usable)  
 BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)  
 BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)  
 BIOS-e820: 0000000000100000 - 000000001f7d0000 (usable)  
 BIOS-e820: 000000001f7d0000 - 000000001f7efc00 (reserved)  
 BIOS-e820: 000000001f7efc00 - 000000001f7fb000 (ACPI NVS)  
 BIOS-e820: 000000001f7fb000 - 000000001f800000 (reserved)  
 BIOS-e820: 00000000e0000000 - 00000000f0000000 (reserved)  
 BIOS-e820: 00000000fec00000 - 00000000fec02000 (reserved)  
 BIOS-e820: 00000000fed20000 - 00000000fed9b000 (reserved)  
 BIOS-e820: 00000000feda0000 - 00000000fedc0000 (reserved)  
 BIOS-e820: 00000000ffb00000 - 00000000ffc00000 (reserved)  
 BIOS-e820: 00000000fff00000 - 0000000100000000 (reserved)  
0MB HIGHMEM available.  
503MB LOWMEM available.  
Memory for crash kernel (0x0 to 0x0) notwithin permissible range  
disabling k[du][]mp  
Using x86 segment limits to approximate NX protection  
On node 0 totalpages: 128976  
  DMA zone: 4096 pages, LIFO batch:0  
  Normal zone: 124880 pages, LIFO batch:31  
DMI 2.3 present.  
Using APIC driver default  
ACPI: RSDP (v000 HP                                    ) @ 0x000fe270  
ACPI: RSDT (v001 HP     30C4     0x31100620 HP   0x00000001) @ 0x1f7efc84  
ACPI: FADT (v002 HP     30C4     0x00000002 HP   0x00000001) @ 0x1f7efc00  
ACPI: MADT (v001 HP     30C4     0x00000001 HP   0x00000001) @ 0x1f7efcb8  
ACPI: MCFG (v001 HP     30C4     0x00000001 HP   0x00000001) @ 0x1f7efd14  
ACPI: SSDT (v001 HP       HPQPpc 0x00001001 MSFT 0x0100000e) @ 0x1f7f6698  
ACPI: DSDT (v001 HP       DAU00  0x00010000 MSFT 0x0100000e) @ 0x00000000  
ACPI: PM-Timer IO Port: 0x1008  
ACPI: Local APIC address 0xfec01000  
ACPI: LAPIC (acpi\_id\[0x01\] lapic\_id\[0x00\] enabled)  
Processor \#0 6:13 APIC version 20  
ACPI: LAPIC\_NMI (acpi\_id\[0x01\] high edge lint\[0x1\])  
ACPI: IOAPIC (id\[0x01\] address\[0xfec00000\] gsi\_base\[0\])  
IOAPIC\[0\]: apic\_id 1, version 32, address 0xfec00000, GSI 0-23  
:

### 示例三 查看dmesg尾部的信息 ###

\[root@new55 ~\]\# dmesg | tail  
Bluetooth: L2CAP ver 2.8  
Bluetooth: L2CAP socket layer initialized  
Bluetooth: RFCOMM socket layer initialized  
Bluetooth: RFCOMM TTY layer initialized  
Bluetooth: RFCOMM ver 1.8  
Bluetooth: HIDP (Human Interface Emulation) ver 1.1  
eth0: no IPv6 routers present  
Installing knfsd (copyright (C) 1996 okir@monad.swb.de).  
NFSD: Using /var/lib/nfs/v4recovery as the NFSv4 [stat][]e recovery directory  
NFSD: starting 90-second grace period  
\[root@new55 ~\]\#

### 示例四 安装SS7卡驱动时的内核日志 ###

\[root@localhost ss7dpk[ln][]x\]\# [cd][] SS7HD\_DRIVER/  
\[root@localhost SS7HD\_DRIVER\]\# ls  
bbdddlnx\_iss.h  bbd\_hbi.h  bbd\_ioc.c  bbd\_isr.c  bbd\_pci.c  BSD\_license.txt  GPL\_V2-only\_license.txt  install\_ss7hd.sh  Makefile26  
bbd\_def.h       bbd\_hs.c   bbd\_ioc.h  bbd\_lnx.c  bbd\_pro.h  build\_ss7hd.sh   i21555.h                 Makefile24  
\[root@localhost SS7HD\_DRIVER\]\# ./build\_ss7hd.sh   
make: Entering directory \`/usr/src/kernels/2.6.9-22.EL-i686'  
  CC \[M\]  /root/[setup][]/ss7dpklnx/SS7HD\_DRIVER/bbd\_hs.o  
  CC \[M\]  /root/setup/ss7dpklnx/SS7HD\_DRIVER/bbd\_ioc.o  
  CC \[M\]  /root/setup/ss7dpklnx/SS7HD\_DRIVER/bbd\_isr.o  
  CC \[M\]  /root/setup/ss7dpklnx/SS7HD\_DRIVER/bbd\_pci.o  
  CC \[M\]  /root/setup/ss7dpklnx/SS7HD\_DRIVER/bbd\_lnx.o  
  LD \[M\]  /root/setup/ss7dpklnx/SS7HD\_DRIVER/ss7hddvr26.o  
  Building modules, stage 2.  
  MODPOST  
  CC      /root/setup/ss7dpklnx/SS7HD\_DRIVER/ss7hddvr26.mod.o  
  LD \[M\]  /root/setup/ss7dpklnx/SS7HD\_DRIVER/ss7hddvr26.ko  
make: Leaving directory \`/usr/src/kernels/2.6.9-22.EL-i686'http://www.linuxso.com/command/dmesg.html

\[root@localhost SS7HD\_DRIVER\]\# ./install\_ss7hd.sh   
\[root@localhost SS7HD\_DRIVER\]\# [lsmod][] | grep ss7  
ss7hddvr26             25808  0  
\[root@localhost SS7HD\_DRIVER\]\# dmesg | tail  
ACPI: PCI interrupt 0000:02:0d.0\[?\] -> GSI 9 (level, low) -> IRQ 9  
BBD\[0\] 64bit  
SS7HD\[0\] - suspend  
  
  
Dialogic SS7HD Device Driver V100.00 (Source V1.21)  
Copyright (C) Dialogic Corporation 2003-2010.  All Rights Reserved  
Using major device number 251.  
ACPI: PCI interrupt 0000:02:0d.0\[?\] -> GSI 9 (level, low) -> IRQ 9  
BBD\[0\] 64bit  
\[root@localhost SS7HD\_DRIVER\]\# ./install\_ss7hd.sh remove  
\[root@localhost SS7HD\_DRIVER\]\# lsmod | grep ss7  
\[root@localhost SS7HD\_DRIVER\]\# dmesg | tail  
BBD\[0\] 64bit  
SS7HD\[0\] - suspend  
  
  
Dialogic SS7HD Device Driver V100.00 (Source V1.21)  
Copyright (C) Dialogic Corporation 2003-2010.  All Rights Reserved  
Using major device number 251.  
ACPI: PCI interrupt 0000:02:0d.0\[?\] -> GSI 9 (level, low) -> IRQ 9  
BBD\[0\] 64bit  
SS7HD\[0\] - suspend  
\[root@localhost SS7HD\_DRIVER\]\#

### 示例五 打印并清除内核环形缓冲区 ###

\[root@new55 ~\]\# dmesg -c  
Linux version 2.6.18-194.el5 (mockbuild@x86-007.build.bos.redhat.com) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)) \#1 SMP Tue Mar 16 21:52:43 EDT 2010  
BIOS-provided physical RAM map:  
 BIOS-e820: 0000000000010000 - 000000000009fc00 (usable)  
 BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)  
 BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)  
 BIOS-e820: 0000000000100000 - 000000001f7d0000 (usable)  
 BIOS-e820: 000000001f7d0000 - 000000001f7efc00 (reserved)  
 BIOS-e820: 000000001f7efc00 - 000000001f7fb000 (ACPI NVS)  
 BIOS-e820: 000000001f7fb000 - 000000001f800000 (reserved)  
 BIOS-e820: 00000000e0000000 - 00000000f0000000 (reserved)  
 BIOS-e820: 00000000fec00000 - 00000000fec02000 (reserved)  
 BIOS-e820: 00000000fed20000 - 00000000fed9b000 (reserved)  
 BIOS-e820: 00000000feda0000 - 00000000fedc0000 (reserved)  
 BIOS-e820: 00000000ffb00000 - 00000000ffc00000 (reserved)  
 BIOS-e820: 00000000fff00000 - 0000000100000000 (reserved)  
0MB HIGHMEM available.  
503MB LOWMEM available.  
Memory for crash kernel (0x0 to 0x0) notwithin permissible range  
disabling k[dump][]  
Using x86 segment limits to approximate NX protection  
On node 0 totalpages: 128976  
  DMA zone: 4096 pages, LIFO batch:0  
  Normal zone: 124880 pages, LIFO batch:31  
DMI 2.3 present.

省略输出

Bluetooth: HIDP (Human Interface Emulation) ver 1.1  
eth0: no IPv6 routers present  
Installing knfsd (copyright (C) 1996 okir@monad.swb.de).  
NFSD: Using /var/lib/nfs/v4recovery as the NFSv4 state recovery directory  
NFSD: starting 90-second grace period  
\[root@new55 ~\]\# dmesg

\[root@new55 ~\]\# less /var/log/dmesg  
Linux version 2.6.18-194.el5 (mockbuild@x86-007.build.bos.redhat.com) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)) \#1 SMP Tue Mar 16 21:52:43 EDT 2010  
BIOS-provided physical RAM map:  
 BIOS-e820: 0000000000010000 - 000000000009fc00 (usable)  
 BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)  
 BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)  
 BIOS-e820: 0000000000100000 - 000000001f7d0000 (usable)  
 BIOS-e820: 000000001f7d0000 - 000000001f7efc00 (reserved)  
 BIOS-e820: 000000001f7efc00 - 000000001f7fb000 (ACPI NVS)  
 BIOS-e820: 000000001f7fb000 - 000000001f800000 (reserved)  
 BIOS-e820: 00000000e0000000 - 00000000f0000000 (reserved)  
 BIOS-e820: 00000000fec00000 - 00000000fec02000 (reserved)  
 BIOS-e820: 00000000fed20000 - 00000000fed9b000 (reserved)  
 BIOS-e820: 00000000feda0000 - 00000000fedc0000 (reserved)  
 BIOS-e820: 00000000ffb00000 - 00000000ffc00000 (reserved)  
 BIOS-e820: 00000000fff00000 - 0000000100000000 (reserved)  
0MB HIGHMEM available.  
503MB LOWMEM available.  
Memory for crash kernel (0x0 to 0x0) notwithin permissible range  
disabling kdump  
Using x86 segment limits to approximate NX protection  
On node 0 totalpages: 128976  
  DMA zone: 4096 pages, LIFO batch:0  
  Normal zone: 124880 pages, LIFO batch:31  
DMI 2.3 present.  
Using APIC driver default  
ACPI: RSDP (v000 HP                                    ) @ 0x000fe270  
ACPI: RSDT (v001 HP     30C4     0x31100620 HP   0x00000001) @ 0x1f7efc84  
ACPI: FADT (v002 HP     30C4     0x00000002 HP   0x00000001) @ 0x1f7efc00  
ACPI: MADT (v001 HP     30C4     0x00000001 HP   0x00000001) @ 0x1f7efcb8  
ACPI: MCFG (v001 HP     30C4     0x00000001 HP   0x00000001) @ 0x1f7efd14  
ACPI: SSDT (v001 HP       HPQPpc 0x00001001 MSFT 0x0100000e) @ 0x1f7f6698  
ACPI: DSDT (v001 HP       DAU00  0x00010000 MSFT 0x0100000e) @ 0x00000000  
ACPI: PM-Timer IO Port: 0x1008  
ACPI: Local APIC address 0xfec01000  
ACPI: LAPIC (acpi\_id\[0x01\] lapic\_id\[0x00\] enabled)  
Processor \#0 6:13 APIC version 20  
ACPI: LAPIC\_NMI (acpi\_id\[0x01\] high edge lint\[0x1\])  
ACPI: IOAPIC (id\[0x01\] address\[0xfec00000\] gsi\_base\[0\])  
IOAPIC\[0\]: apic\_id 1, version 32, address 0xfec00000, GSI 0-23  
\[root@new55 ~\]\#

http://www.linuxso.com/command/dmesg.html

[mesg]: http://www.linuxso.com/command/mesg.html
[dmesg]: http://www.linuxso.com/command/dmesg.html
[Link 1]: http://www.linuxso.com/command/
[less]: http://www.linuxso.com/command/less.html
[grep]: http://www.linuxso.com/command/grep.html
[id]: http://www.linuxso.com/command/id.html
[set]: http://www.linuxso.com/command/set.html
[dd]: http://www.linuxso.com/command/dd.html
[su]: http://www.linuxso.com/command/su.html
[cp]: http://www.linuxso.com/command/cp.html
[egrep]: http://www.linuxso.com/command/egrep.html
[enable]: http://www.linuxso.com/command/enable.html
[rm]: http://www.linuxso.com/command/rm.html
[ex]: http://www.linuxso.com/command/ex.html
[file]: http://www.linuxso.com/command/file.html
[who]: http://www.linuxso.com/command/who.html
[ls]: http://www.linuxso.com/command/ls.html
[uname]: http://www.linuxso.com/command/uname.html
[du]: http://www.linuxso.com/command/du.html
[stat]: http://www.linuxso.com/command/stat.html
[ln]: http://www.linuxso.com/command/ln.html
[cd]: http://www.linuxso.com/command/cd.html
[setup]: http://www.linuxso.com/command/setup.html
[lsmod]: http://www.linuxso.com/command/lsmod.html
[dump]: http://www.linuxso.com/command/dump.html