linux 日志查看 dmesg七种用法清空dmesg

深碍√TFBOYSˉ_ 2021-08-26 19:45 4754阅读 0赞

**目录**

1. 列出加载到内核中的所有驱动

2. 列出所有被检测到的硬件

3. 只输出dmesg命令的前20行日志

4. 只输出dmesg命令最后20行日志

5. 搜索包含特定字符串的被检测到的硬件

6. 清空dmesg缓冲区日志

7. 实时监控dmesg日志输出

--------------------

dmesg 命令的使用范例

‘dmesg’命令设备故障的诊断是非常重要的。在‘dmesg’命令的帮助下进行硬件的连接或断开连接操作时，我们可以看到硬件的检测或者断开连接的信息。‘dmesg’命令在多数基于**Linux**和**Unix**的操作系统中都可以使用。

下面我们展示一些最负盛名的‘dmesg’命令工具以及其实际使用举例。‘dmesg’命令的使用语法如下。

\# dmesg \[options...\]

### 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。

\[root@tecmint.com ~\]\# dmesg | more

\[root@tecmint.com ~\]\# 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：

\[root@tecmint.com ~\]\# 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。

\[root@tecmint.com ~\]\# 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。

\[root@tecmint.com ~\]\# 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

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][grep] 的‘**-i**’选项表示忽略大小写。

\[root@tecmint.com log\]\# dmesg | grep -i usb

\[root@tecmint.com log\]\# dmesg | grep -i dma

\[root@tecmint.com log\]\# dmesg | grep -i tty

\[root@tecmint.com log\]\# 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。

\[root@tecmint.com log\]\# dmesg -c

### 7. 实时监控dmesg日志输出 ###