我使用过的Linux命令之dmesg - 查看开机信息/打印或控制内核环形缓冲区

本文链接：http://codingstandards.iteye.com/blog/837486 （转载请注明出处）

用途说明

dmesg命令用于打印Linux系统开机启动信息，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（print or control the kernel ring buffer）。开机信息亦保存在/var/log/dmesg的文件里。某些硬件设备（比如七号信令卡、语音卡之类）在安装的时候，通常会安装驱动程序（内核模块），会打印一些信息，就可以通过dmesg命令来查看。

常用参数

格式：dmesg

查看开机信息。

格式：dmesg -c

清除开机信息，但/var/log/dmesg文件中仍然有这些信息。

因为dmesg命令输出的东西有点多，通常与less/more/tail/grep等命令配合使用。

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 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 12:55 boot.messages

[root@new55 ~]# mail -s "Boot Log of Linux Server" [email protected] <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 ([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 [email protected]).
NFSD: Using /var/lib/nfs/v4recovery as the NFSv4 state recovery directory
NFSD: starting 90-second grace period
[root@new55 ~]#

示例四安装SS7卡驱动时的内核日志

[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'
[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 ([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.

省略输出

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 ~]#