dmesg 命令
dmesg 这个命令，Linux下用的还是比较多的。现在来详细看一下：
Linux dmesg命令用于显示开机信息。
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。开机信息亦保存在/var/log目录中，名称为dmesg的文件里。
一、语法
dmesg [-cn][-s <缓冲区大小>]
二、选项
-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。
$ dmesg -h
Usage:
dmesg [options]
Options:
-C, --clear clear the kernel ring buffer
-c, --read-clear read and clear all messages
-D, --console-off disable printing messages to console
-d, --show-delta show time delta between printed messages
-E, --console-on enable printing messages to console
-f, --facility restrict output to defined facilities
-h, --help display this help and exit
-k, --kernel display kernel messages
-l, --level restrict output to defined levels
-n, --console-level
-r, --raw print the raw message buffer
-s, --buffer-size
-T, --ctime show human readable timestamp (could be
inaccurate if you have used SUSPEND/RESUME)
-t, --notime don't print messages timestamp
-u, --userspace display userspace messages
-V, --version output version information and exit
-x, --decode decode facility and level to readable string
Supported log facilities:
kern - kernel messages
user - random user-level messages
mail - mail system
daemon - system daemons
auth - security/authorization messages
syslog - messages generated internally by syslogd
lpr - line printer subsystem
news - network news subsystem
Supported log levels (priorities):
emerg - system is unusable
alert - action must be taken immediately
crit - critical conditions
err - error conditions
warn - warning conditions
notice - normal but significant condition
info - informational
debug - debug-level messages
三、实例
root@dm368-evm:/# dmesg
>Bad block table found at page 262080, version 0x01
Bad block table found at page 262016, version 0x01
nand_bbt: ECC error while reading bad block table
nand_read_bbt: Bad block at 0x00000ff00000
nand_read_bbt: Bad block at 0x00000ff20000
nand_read_bbt: Bad block at 0x00000ff40000
nand_read_bbt: Bad block at 0x00000ff60000
nand_read_bbt: Bad block at 0x00000ff80000
nand_read_bbt: Bad block at 0x00000ffa0000
nand_read_bbt: Bad block at 0x00000ffc0000
nand_read_bbt: Bad block at 0x00000ffe0000
Creating 5 MTD partitions on "davinci_nand.0":
0x000000000000-0x0000003c0000 : "bootloader"
0x0000003c0000-0x000000400000 : "params"
0x000000400000-0x000000820000 : "kernel"
0x000000820000-0x000008820000 : "filesystem"
0x000008820000-0x000020000000 : "zslf"
davinci_nand davinci_nand.0: controller rev. 2.3
UBI: attaching mtd3 to ubi0
UBI: physical eraseblock size: 131072 bytes (128 KiB)
UBI: logical eraseblock size: 126976 bytes
UBI: smallest flash I/O unit: 2048
UBI: VID header offset: 2048 (aligned 2048)
UBI: data offset: 4096
UBI: attached mtd3 to ubi0
UBI: MTD device name: "filesystem"
UBI: MTD device size: 128 MiB
UBI: number of good PEBs: 1024
UBI: number of bad PEBs: 0
UBI: max. allowed volumes: 128
UBI: wear-leveling threshold: 4096
UBI: number of internal volumes: 1
UBI: number of user volumes: 1
UBI: available PEBs: 5
UBI: total number of reserved PEBs: 1019
UBI: number of PEBs reserved for bad PEB handling: 10
UBI: max/mean erase counter: 20/11
UBI: image sequence number: 0
UBI: background thread "ubi_bgt0d" started, PID 343
PPP generic driver version 2.4.2
PPP Deflate Compression module registered
PPP BSD Compression module registered
PPP MPPE Compression module registered
NET: Registered protocol family 24
tun: Universal TUN/TAP device driver, 1.6
tun: (C) 1999-2004 Max Krasnyansky
console [netcon0] enabled
netconsole: network logging started
Initializing USB Mass Storage driver...
usbcore: registered new interface driver usb-storage
USB Mass Storage support registered.
usbcore: registered new interface driver usbserial
USB Serial support registered for generic
usbcore: registered new interface driver usbserial_generic
usbserial: USB Serial Driver core
USB Serial support registered for GSM modem (1-port)
usbcore: registered new interface driver option
option: v0.7.2:USB Driver for GSM modems
usbcore: registered new interface driver usbtest
rtc-ds1307 1-0068: rtc core: registered ds1339 as rtc0
i2c /dev entries driver
Linux video capture interface: v2.00
ths7303 1-002c: chip found @ 0x58 (DaVinci I2C adapter)
ths7303 1-002c: ths7303 write failed
ths7303: probe of 1-002c failed with error -121
vpfe_init
vpfe-capture: vpss clock vpss_master enabled
vpfe-capture vpfe-capture: v4l2 device registered
vpfe-capture vpfe-capture: video device registered
dm365evm_enable_pca9543a
dm365evm_enable_pca9543a, status = -121
EVM: switch to HD imager video input
mt9p031 1-005d: Detected a MT9P031 chip ID 1801
mt9p031 1-005d: mt9p031 1-005d decoder driver registered !!
vpfe-capture vpfe-capture: v4l2 sub device mt9p031 registered
vpfe_register_ccdc_device: DM365 ISIF
DM365 ISIF is registered with vpfe.
af major#: 250, minor# 0
AF Driver initialized
aew major#: 249, minor# 0
AEW Driver initialized
###### osd_init ######
### VPBE OSD DRIVER INIT ###
Trying to register davinci display video device.
layer=c112d000,layer->video_dev=c112d170
Trying to register davinci display video device.
layer=c112d400,layer->video_dev=c112d570
davinci_init:DaVinci V4L2 Display Driver V1.0 loaded
watchdog watchdog: heartbeat 60 sec
davinci_mmc davinci_mmc.0: Using DMA, 4-bit mode
Advanced Linux Sound Architecture Driver Version 1.0.21.
No device for DAI tlv320aic3x
No device for DAI davinci-i2s
asoc: tlv320aic3x <-> davinci-i2s mapping ok
ALSA device list:
#0: DaVinci EVM (tlv320aic3x)
TCP cubic registered
NET: Registered protocol family 17
Clocks: disable unused mmcsd1
Clocks: disable unused spi0
Clocks: disable unused spi1
Clocks: disable unused spi2
Clocks: disable unused spi3
Clocks: disable unused spi4
Clocks: disable unused pwm0
Clocks: disable unused pwm1
Clocks: disable unused pwm2
Clocks: disable unused pwm3
Clocks: disable unused timer1
Clocks: disable unused timer3
Clocks: disable unused emac
Clocks: disable unused voice_codec
Clocks: disable unused rto
Clocks: disable unused mjcp
davinci_emac_probe: using random MAC addr: 32:be:8d:46:68:be
emac-mii: probed
rtc-ds1307 1-0068: setting system clock to 2015-12-05 11:04:18 UTC (1449313458)
UBIFS: mounted UBI device 0, volume 0, name "rootfs"
UBIFS: file system size: 126341120 bytes (123380 KiB, 120 MiB, 995 LEBs)
UBIFS: journal size: 6348800 bytes (6200 KiB, 6 MiB, 50 LEBs)
UBIFS: media format: w4/r0 (latest is w4/r0)
UBIFS: default compressor: lzo
UBIFS: reserved for root: 4952683 bytes (4836 KiB)
VFS: Mounted root (ubifs filesystem) on device 0:14.
Freeing init memory: 144K
udev: starting version 141
eth0: attached PHY driver [LXT971] (mii_bus:phy_addr=1:01, id=1378e2)
CMEMK module: built on Mar 24 2011 at 16:58:03
Reference Linux version 2.6.32
File /sdk/build/DVSDK_4_02/4_02_00_06/arago-install/arago-tmp/work/dm368-evm-none-linux-gnueabi/ti-linuxutils-1_2_26_01_02-r52d/linuxutils_2_26_01_02/packages/ti/sdo/linuxutils/cmem/src/module/cmemk.c
allocated heap buffer 0xc7000000 of size 0x4400000
heap fallback enabled - will try heap if pool buffer is not available
CMEM Range Overlaps Kernel Physical - allowing overlap
CMEM phys_start (0x1000) overlaps kernel (0x80000000 -> 0x83000000)
cmemk initialized
PHY: 1:01 - Link is Up - 100/Full
IRQK module: built on Mar 24 2011 at 16:58:17
Reference Linux version 2.6.32
File /sdk/build/DVSDK_4_02/4_02_00_06/arago-install/arago-tmp/work/dm368-evm-none-linux-gnueabi/ti-linuxutils-1_2_26_01_02-r52d/linuxutils_2_26_01_02/packages/ti/sdo/linuxutils/irq/src/module/irqk.c
irqk initialized
EDMAK module: built on Mar 24 2011 at 16:58:11
Reference Linux version 2.6.32
File /sdk/build/DVSDK_4_02/4_02_00_06/arago-install/arago-tmp/work/dm368-evm-none-linux-gnueabi/ti-linuxutils-1_2_26_01_02-r52d/linuxutils_2_26_01_02/packages/ti/sdo/linuxutils/edma/src/module/edmak.c
###### output_store ######
###### davinci_get_cur_encoder ######
VPBE Encoder de-initialized
###### vpbe_encoder_initialize ######
###### output is COMPOSITE,outindex is 0 ######
###### vpbe_encoder_setoutput ######
Setting output to Composite
Start of vpbe_encoder_setmode..
###### dm365 = 1 ######
###### mode_info->std is 1 ######
###### mode is NTSC ######
VPBE Encoder initialized
###### 22VPBE Encoder initialized ######
###### vpbe_encoder_setoutput ######
Setting output to Component Video
Start of vpbe_encoder_setmode..
###### dm365 = 1 ######
###### mode_info->std is 1 ######
###### mode is 480P-60 ######
###### davinci_enc_set_output : next davinci_enc_set_mode_platform ######
###### davinci_enc_set_mode_platform : next davinci_enc_priv_setmode ######
###### output_show ######
###### davinci_enc_get_output ######
###### davinci_get_cur_encoder ######
###### mode_store ######
###### davinci_enc_get_mode ######
###### davinci_get_cur_encoder ######
###### davinci_enc_set_mode ######
###### davinci_get_cur_encoder ######
Start of vpbe_encoder_setmode..
###### dm365 = 1 ######
###### mode_info->std is 1 ######
###### mode is 576P-50 ######
###### davinci_enc_set_mode : next davinci_enc_set_mode ######
###### davinci_enc_set_mode_platform : next davinci_enc_priv_setmode ######
###### mode_show ######
###### davinci_enc_get_mode ######
###### davinci_get_cur_encoder ######
###### davinci_enc_get_mode ######
###### davinci_get_cur_encoder ######
###### davinci_enc_get_mode ######
###### davinci_get_cur_encoder ######
###### davinci_enc_set_mode ######
###### davinci_get_cur_encoder ######
Start of vpbe_encoder_setmode..
###### dm365 = 1 ######
###### mode_info->std is 1 ######
###### mode is 576P-50 ######
###### davinci_enc_set_mode : next davinci_enc_set_mode ######
###### davinci_enc_set_mode_platform : next davinci_enc_priv_setmode ######
###### davinci_enc_get_mode ######
###### davinci_get_cur_encoder ######
###### davinci_enc_get_mode ######
###### davinci_get_cur_encoder ######
###### davinci_enc_get_mode ######
###### davinci_get_cur_encoder ######
davinci_resizer davinci_resizer.2: RSZ_G_CONFIG:0:1:124
davinci_previewer davinci_previewer.2: ipipe_set_preview_config
davinci_previewer davinci_previewer.2: ipipe_set_preview_config
vpfe-capture vpfe-capture: IPIPE Chained
vpfe-capture vpfe-capture: Resizer present
dm365evm_enable_pca9543a
dm365evm_enable_pca9543a, status = -121
EVM: switch to HD imager video input
######vpfe_dev->current_subdev->is_camera.
-----Exposure time = 2f2############
v4l2_device_call_until_err sdinfo->grp_id : 4.
-----Exposure time = 2f2
vpfe-capture vpfe-capture: width = 1280, height = 720, bpp = 1
vpfe-capture vpfe-capture: adjusted width = 1280, height = 720, bpp = 1, bytesperline = 1280, sizeimage = 1382400
vpfe-capture vpfe-capture: width = 1280, height = 720, bpp = 1
vpfe-capture vpfe-capture: adjusted width = 1280, height = 720, bpp = 1, bytesperline = 1280, sizeimage = 1382400
ipipe_set_resizer, resizer - A enabled
四、与管道一起使用
参看：Linux系统中‘dmesg’命令处理故障和收集系统信息的7种用法
（1）列出加载到内核中的所有驱动
我们可以使用如‘more’。 ‘tail’, ‘less ’或者‘grep’文字处理工具来处理‘dmesg’命令的输出。由于dmesg日志的输出不适合在一页中完全显示，因此我们使用管道（pipe）将其输出送到more或者less命令单页显示。
[[email protected] ~]# dmesg | more
[[email protected] ~]# dmesg | less
输出：
[ 0.000000] Initializing cgroup subsys cpuset
[ 0.000000] Initializing cgroup subsys cpu
[ 0.000000] Initializing cgroup subsys cpuacct
[ 0.000000] Linux version 3.11.0-13-generic (buildd@aatxe) (gcc version 4.8.1 (Ubuntu/Linaro 4.8.1-10ubuntu8) ) #20-Ubuntu SMP Wed Oct 23 17:26:33 UTC 2013
(Ubuntu 3.11.0-13.20-generic 3.11.6)
[ 0.000000] KERNEL supported cpus:
[ 0.000000] Intel GenuineIntel
[ 0.000000] AMD AuthenticAMD
[ 0.000000] NSC Geode by NSC
[ 0.000000] Cyrix CyrixInstead
[ 0.000000] Centaur CentaurHauls
[ 0.000000] Transmeta GenuineTMx86
[ 0.000000] Transmeta TransmetaCPU
[ 0.000000] UMC UMC UMC UMC
[ 0.000000] e820: BIOS-provided physical RAM map:
[ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
[ 0.000000] BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
[ 0.000000] BIOS-e820: [mem 0x0000000000100000-0x000000007dc08bff] usable
[ 0.000000] BIOS-e820: [mem 0x000000007dc08c00-0x000000007dc5cbff] ACPI NVS
[ 0.000000] BIOS-e820: [mem 0x000000007dc5cc00-0x000000007dc5ebff] ACPI data
[ 0.000000] BIOS-e820: [mem 0x000000007dc5ec00-0x000000007fffffff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000e0000000-0x00000000efffffff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000fec00000-0x00000000fed003ff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000fed20000-0x00000000fed9ffff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000fee00000-0x00000000feefffff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000ffb00000-0x00000000ffffffff] reserved
[ 0.000000] NX (Execute Disable) protection: active
.....
2、 列出所有被检测到的硬件
要显示所有被内核检测到的硬盘设备，你可以使用‘grep’命令搜索‘sda’关键词，如下：
[[email protected] ~]# dmesg | grep sda
[ 1.280971] sd 2:0:0:0: [sda] 488281250 512-byte logical blocks: (250 GB/232 GiB)
[ 1.281014] sd 2:0:0:0: [sda] Write Protect is off
[ 1.281016] sd 2:0:0:0: [sda] Mode Sense: 00 3a 00 00
[ 1.281039] sd 2:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
[ 1.359585] sda: sda1 sda2 < sda5 sda6 sda7 sda8 >
[ 1.360052] sd 2:0:0:0: [sda] Attached SCSI disk
[ 2.347887] EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null)
[ 22.928440] Adding 3905532k swap on /dev/sda6. Priority:-1 extents:1 across:3905532k FS
[ 23.950543] EXT4-fs (sda1): re-mounted. Opts: errors=remount-ro
[ 24.134016] EXT4-fs (sda5): mounted filesystem with ordered data mode. Opts: (null)
[ 24.330762] EXT4-fs (sda7): mounted filesystem with ordered data mode. Opts: (null)
[ 24.561015] EXT4-fs (sda8): mounted filesystem with ordered data mode. Opts: (null)
注解： ‘sda’表示第一块 SATA硬盘，‘sdb’表示第二块SATA硬盘。若想查看IDE硬盘搜索‘hda’或‘hdb’关键词。
3、只输出dmesg命令的前20行日志
在‘dmesg’命令后跟随‘head’命令来显示开始几行，‘dmesg | head -20′命令将显示开始的前20行。
[[email protected] ~]# dmesg | head -20
[ 0.000000] Initializing cgroup subsys cpuset
[ 0.000000] Initializing cgroup subsys cpu
[ 0.000000] Initializing cgroup subsys cpuacct
[ 0.000000] Linux version 3.11.0-13-generic (buildd@aatxe) (gcc version 4.8.1 (Ubuntu/Linaro 4.8.1-10ubuntu8) ) #20-Ubuntu SMP Wed Oct 23 17:26:33 UTC 2013 (Ubuntu 3.11.0-13.20-generic 3.11.6)
[ 0.000000] KERNEL supported cpus:
[ 0.000000] Intel GenuineIntel
[ 0.000000] AMD AuthenticAMD
[ 0.000000] NSC Geode by NSC
[ 0.000000] Cyrix CyrixInstead
[ 0.000000] Centaur CentaurHauls
[ 0.000000] Transmeta GenuineTMx86
[ 0.000000] Transmeta TransmetaCPU
[ 0.000000] UMC UMC UMC UMC
[ 0.000000] e820: BIOS-provided physical RAM map:
[ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
[ 0.000000] BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
[ 0.000000] BIOS-e820: [mem 0x0000000000100000-0x000000007dc08bff] usable
[ 0.000000] BIOS-e820: [mem 0x000000007dc08c00-0x000000007dc5cbff] ACPI NVS
[ 0.000000] BIOS-e820: [mem 0x000000007dc5cc00-0x000000007dc5ebff] ACPI data
[ 0.000000] BIOS-e820: [mem 0x000000007dc5ec00-0x000000007fffffff] reserved
4、只输出dmesg命令最后20行日志
在‘dmesg’命令后跟随‘tail’命令（‘ dmesg | tail -20’）来输出‘dmesg’命令的最后20行日志，当你插入可移动设备时它是非常有用的。
[[email protected] ~]# dmesg | tail -20
parport0: PC-style at 0x378, irq 7 [PCSPP,TRISTATE]
ppdev: user-space parallel port driver
EXT4-fs (sda1): mounted filesystem with ordered data mode
Adding 2097144k swap on /dev/sda2. Priority:-1 extents:1 across:2097144k
readahead-disable-service: delaying service auditd
ip_tables: (C) 2000-2006 Netfilter Core Team
nf_conntrack version 0.5.0 (16384 buckets, 65536 max)
NET: Registered protocol family 10
lo: Disabled Privacy Extensions
e1000: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: None
Slow work thread pool: Starting up
Slow work thread pool: Ready
FS-Cache: Loaded
CacheFiles: Loaded
CacheFiles: Security denies permission to nominate security context: error -95
eth0: no IPv6 routers present
type=1305 audit(1398268784.593:18630): audit_enabled=0 old=1 auid=4294967295 ses=4294967295 res=1
readahead-collector: starting delayed service auditd
readahead-collector: sorting
readahead-collector: finished
5、搜索包含特定字符串的被检测到的硬件
由于‘dmesg’命令的输出实在太长了，在其中搜索某个特定的字符串是非常困难的。因此，有必要过滤出一些包含‘usb’ ‘dma’ ‘tty’ ‘memory’等字符串的日志行。grep 命令 的‘-i’选项表示忽略大小写。
[[email protected] log]# dmesg | grep -i usb
[[email protected] log]# dmesg | grep -i dma
[[email protected] log]# dmesg | grep -i tty
[[email protected] log]# dmesg | grep -i memory
输出：
[ 0.000000] Scanning 1 areas for low memory corruption
[ 0.000000] initial memory mapped: [mem 0x00000000-0x01ffffff]
[ 0.000000] Base memory trampoline at [c009b000] 9b000 size 16384
[ 0.000000] init_memory_mapping: [mem 0x00000000-0x000fffff]
[ 0.000000] init_memory_mapping: [mem 0x37800000-0x379fffff]
[ 0.000000] init_memory_mapping: [mem 0x34000000-0x377fffff]
[ 0.000000] init_memory_mapping: [mem 0x00100000-0x33ffffff]
[ 0.000000] init_memory_mapping: [mem 0x37a00000-0x37bfdfff]
[ 0.000000] Early memory node ranges
[ 0.000000] PM: Registered nosave memory: [mem 0x0009f000-0x000effff]
[ 0.000000] PM: Registered nosave memory: [mem 0x000f0000-0x000fffff]
[ 0.000000] please try 'cgroup_disable=memory' option if you don't want memory cgroups
[ 0.000000] Memory: 2003288K/2059928K available (6352K kernel code, 607K rwdata, 2640K rodata, 880K init, 908K bss, 56640K reserved, 1146920K highmem)
[ 0.000000] virtual kernel memory layout:
[ 0.004291] Initializing cgroup subsys memory
[ 0.004609] Freeing SMP alternatives memory: 28K (c1a3e000 - c1a45000)
[ 0.899622] Freeing initrd memory: 23616K (f51d0000 - f68e0000)
[ 0.899813] Scanning for low memory corruption every 60 seconds
[ 0.946323] agpgart-intel 0000:00:00.0: detected 32768K stolen memory
[ 1.360318] Freeing unused kernel memory: 880K (c1962000 - c1a3e000)
[ 1.429066] [drm] Memory usable by graphics device = 2048M
6、清空dmesg缓冲区日志
我们可以使用如下命令来清空dmesg的日志。该命令会清空dmesg环形缓冲区中的日志。但是你依然可以查看存储在‘/var/log/dmesg’文件中的日志。你连接任何的设备都会产生dmesg日志输出。
[[email protected] log]# dmesg -c
7、实时监控dmesg日志输出
在某些发行版中可以使用命令‘tail -f /var/log/dmesg’来实时监控dmesg的日志输出。
[[email protected] log]# watch "dmesg | tail -20"
结论： dmesg命令在系统dmesg记录实时更改或产生的情况下是非常有用的。你可以使用man dmesg来获取更多关于dmesg的信息。
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作者：聚优致成
来源：CSDN
原文：https://blog.csdn.net/qq_29350001/article/details/79062948
版权声明：本文为博主原创文章，转载请附上博文链接！