linux dmesg命令詳解

linux dmesg命令引數及用法詳解(linux顯示開機資訊命令)

功能說明：顯示開機資訊。

語 法：dmesg [-cn][-s 緩衝區大小]

補充說明：kernel會將開機資訊儲存在ring buffer中。您若是開機時來不及檢視資訊，可利用dmesg來檢視。開機資訊亦儲存在/var/log目錄中，名稱為dmesg的檔案裡。

參 數：

-c 顯示資訊後，清除ring buffer中的內容。

-s緩衝區大小 預設定為8196，剛好等於ring buffer的大小。

-n 設定記錄資訊的層級。擴充套件閱讀一:dmesg命令主要用途

主要應用：

dmesg用來顯示核心環緩衝區（kernel-ring buffer）內容，核心將各種訊息存放在這裡。在系統引導時，核心將與硬體和模組初始化相關的資訊填到這個緩衝區中。核心環緩衝區中的訊息對於診斷系統問題 通常非常有用。在執行dmesg時，它顯示大量資訊。通常透過less或grep使用管道檢視dmesg的輸出，這樣可以更容易找到待查資訊。例如，如果發現硬碟效能低下，可以使用dmesg來檢查它們是否執行在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裝置正在什麼模式下執行。如果乙太網連接出現問題，那麼可以在dmesg日誌中搜索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，那麼dmesg顯示每個網絡卡的硬體配置資訊。如果某項系統服務未能得到正確的配置，dmesg日誌很快就填滿錯誤訊息，這是診斷故障的良好起點。

還可以用來探測系統核心模組的載入情況，比如要檢測ACPI的載入情況，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

擴充套件閱讀二：dmesg命令使用示例

使用示例

示例一 將開機資訊發郵件

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" [email protected] boot.messages

[root@new55 ~]#示例二 瀏覽dmesg輸出的資訊

[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 ([email protected]) (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 檢視dmesg尾部的資訊

[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 [email protected]).

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卡驅動時的核心日誌

[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-i686http://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 列印並清除核心環形緩衝區

[root@new55 ~]# dmesg -c

Linux version 2.6.18-194.el5 ([email protected]) (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 [email protected]).

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 ([email protected]) (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 ~]#

dmesg是Linux系統中一個非常有用的命令，它可以顯示核心環緩衝區的內容，包括啟動資訊、硬體資訊、驅動程式資訊等。下面是dmesg命令的詳解：
1. 命令格式：dmesg
2. 顯示核心資訊：dmesg命令可以顯示核心啟動時的資訊，包括核心版本、啟動時間、CPU資訊等。
3. 顯示硬體資訊：dmesg命令可以顯示硬體資訊，包括CPU、記憶體、硬碟、網絡卡等。
總之，dmesg命令是Linux系統中一個非常有用的命令，可以幫助使用者瞭解系統的執行情況，排查問題，提高系統的穩定性和安全性。

dmesg是一個Linux系統管理工具，用於列印作業系統核心環緩衝區中的日誌資訊（Kernel Ring Buffer）。它可以幫助使用者瞭解核心相關資訊，如硬體故障、啟動資訊、驅動程式、中斷等。dmesg命令可以提供以下一些引數：

1. -c: 清空緩衝區並檢視所有日誌資訊。

2. -s: 只顯示緩衝區中指定位元組數之內的日誌資訊。

3. -d: 列印除錯級別的日誌資訊。

4. -w: 持續列印新增的日誌資訊，這個引數通常在系統啟動時檢視非常有用。

現在我們可以透過下面的一些示例來了解如何使用dmesg命令：

1. 檢視系統啟動資訊：可以使用以下命令來檢視Linux系統啟動時的日誌資訊。

```

dmesg | less

```

透過less命令，可以檢視整個日誌檔案。

2. 檢視硬體資訊：可以使用以下命令檢視Linux作業系統與硬體有關的資訊。

```

dmesg | grep #39;hardware_name#39;

```

此處“hardware_name”是指硬體裝置名稱。

3. 檢視系統操作的相關訊息：可以使用以下命令檢視系統操作方面的相關訊息。

```

dmesg | grep #39;system_message#39;

```

其中“system_message”指系統訊息。

這只是dmesg命令的一些示例，dmesg命令還有許多引數和選項可供使用，可以根據自己的需要使用這些引數。

1. dmesg命令是Linux系統中的一個工具，用於檢視核心環境下的系統日誌資訊。
2. dmesg命令可以輸出核心環境下的各種資訊，包括啟動資訊、硬體資訊、驅動資訊等等，這些資訊對於系統的除錯和故障排除非常有幫助。
3. 此外，dmesg命令還可以與其他命令結合使用，比如grep命令，可以透過過濾關鍵字來查詢特定的資訊。
同時，dmesg命令也可以將輸出結果儲存到檔案中，方便後續分析和處理。