linux dmesg命令參數及用法詳解(linux顯示開機信息命令)

功能說明：顯示開機信息。

語　　法：dmesg [-cn][-s <緩沖區大小>]

補充說明：kernel會將開機信息存儲在ring buffer中。您若是開機時來不及查看信息，可利用dmesg來查看。開機信息亦保存在/var/log目錄中，名稱為dmesg的文件里。

參　　數：
　-c 　顯示信息后，清除ring buffer中的內容。 
　-s<緩沖區大小> 　預設置為8196，剛好等於ring buffer的大小。 
　-n 　設置記錄信息的層級。

擴展閱讀一:dmesg命令主要用途

 

主要應用：

dmesg用來顯示內核環緩沖區（kernel-ring buffer）內容，內核將各種消息存放在這里。在系統引導時，內核將與硬件和模塊初始化相關的信息填到這個緩沖區中。內核環緩沖區中的消息對於診斷系統問題 通常非常有用。在運行dmesg時，它顯示大量信息。通常通過less或grep使用管道查看dmesg的輸出，這樣可以更容易找到待查信息。例如，如果發現硬盤性能低下，可以使用dmesg來檢查它們是否運行在DMA模式：

$dmesg | grep DMA
...
ide0: BM-DMA at 0xf000-0xf007, BIOS settings: hda:DMA, hdb:DMA
ide1: BM-DMA at 0xf008-0xf00f, BIOS settings: hdc:DMA, hdd:DMA
...

上面幾行可以說明每個IDE設備正在什么模式下運行。如果以太網連接出現問題，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: subsystem: 0147b:1c00
bound to 0000:00:04.0
eth0: no IPv6 routers present

如果一切正常，那么dmesg顯示每個網卡的硬件配置信息。如果某項系統服務未能得到正確的配置，dmesg日志很快就填滿錯誤消息，這是診斷故障的良好起點。

還可以用來探測系統內核模塊的加載情況，比如要檢測ACPI的加載情況，使用dmesg | grep acpi

 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 enabled  

  ACPI: System firmware supports: C2  

  ACPI: plvl2lat=99 plvl3lat=1001 

  ACPI: C2 enter=1417 C2 exit=354 

  ACPI: C3 enter=-1 C3 exit=-1 

  ACPI: Not using ACPI idle 

  ACPI: System firmware supports: S0 S1 S4 S5

擴展閱讀二：dmesg命令使用示例

 

使用示例

示例一 將開機信息發郵件

man dmesg 寫道

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  whoever 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 免費  end_of_the_skype_highlighting:55 boot.messages

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

示例二 瀏覽dmesg輸出的信息

[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 ([e-mail]) (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
:

 

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 [e-mail]).
NFSD: Using /var/lib/nfs/v4recovery as the NFSv4 state recovery directory
NFSD: starting 90-second grace period
[root@new55 ~]#

 

示例四 安裝SS7卡驅動時的內核日志

[root@localhost ss7dpklnx]# 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 打印並清除內核環形緩沖區

[root@new55 ~]# dmesg -c
Linux version 2.6.18-194.el5 ([e-mail]) (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.

省略輸出

Bluetooth: HIDP (Human Interface Emulation) ver 1.1
eth0: no IPv6 routers present
Installing knfsd (copyright (C) 1996 [e-mail]).
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 ([e-mail]) (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 ~]#

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