7个'dmesg'命令在Linux系统的故障排除和收集信息的命令

\'dmesg\'命令显示来自内核环形缓冲区的关于许多信息的消息,如系统架构,cpu,附加设备,RAM等。

'dmesg '命令将显示内核环缓冲区的消息。系统通过多个运行级别,从那里我们可以获得大量的信息,如系统架构,cpu,附加设备,RAM等。当计算机启动时,内核(操作系统的核心)被加载到内存中。在此期间,显示的消息数量,我们可以看到内核检测到的硬件设备。 另请阅读10个Linux命令来收集系统和硬件信息
dmesg命令示例

dmesg命令示例

在设备故障的情况下,消息在诊断目的方面非常重要。当我们在系统上连接或断开硬件设备时,在dmesg命令的帮助下,我们即时知道检测到的或断开的信息。dmesg命令可在大多数Linux和Unix为基础的操作系统。 让我们对一些名为“dmesg”命令的着名工具以及他们的实际例子做一些介绍。 dmesg的确切语法如下。
# dmseg [options...]

1.在内核中列出所有加载的驱动程序

我们可以用文本处理工具,即' ',' 尾巴 ',' '或'grep'可以用dmesg命令。由于dmesg日志的输出不适合单个页面,因此使用dmesg with pipe或多或少命令将在单个页面中显示日志。
[root@howtoing.com ~]# dmesg | more
[root@howtoing.com ~]# dmesg | less
示例输出
[    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
.....
阅读也管理Linux文件可有效地使用命令头,tail 和 cat

2.列出所有检测到的设备

要发现其中的硬盘已经被内核检测到,您可以搜索关键字“SDA”“grep”沿如下所示。
[root@howtoing.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)
:“SDA”第一个SATA硬盘,'深发展'是第二个SATA硬盘驱动器等。在IDE硬盘驱动器的情况下,使用“hda”或“hdb”搜索。

3.仅打印前20行输出

“head”和dmesg将显示起始行,即'dmesg |头-20'将只从起点打印20行。
[root@howtoing.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.仅打印最后20行输出

'tail'和dmesg命令将只打印最后20行,这在我们插入可移动设备的情况下很有用。
[root@howtoing.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
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.搜索检测到的设备或特定字符串

由于dmesg输出的长度,很难搜索特定的字符串。因此,随着遇到的字符串,如“USB”“DMA”“TTY”和“ 记忆 ”等。“-i”选项指示来筛选行grep命令忽略的情况下(大写或小写字母)。
[root@howtoing.com log]# dmesg | grep -i usb
[root@howtoing.com log]# dmesg | grep -i dma
[root@howtoing.com log]# dmesg | grep -i tty
[root@howtoing.com log]# dmesg | grep -i memory
示例输出
[    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.清除dmesg缓冲区日志

是的,我们可以清除dmesg日志,如果需要使用以下命令。它将清除dmesg环缓冲区消息日志,直到您执行以下命令。你仍然可以查看存储在' 在/ var /日志/ dmesg的 “文件日志。如果连接任何设备都会生成dmesg输出。
[root@howtoing.com log]# dmesg -c

7.实时监控dmesg

一些发行版允许命令'tail -f / var / log / dmesg'以及实时dmesg监控。
[root@howtoing.com log]# watch "dmesg | tail -20"
结论 :dmesg命令是dmesg的记录所有系统更改完成或实时发生的有用。 与往常一样,你可以男人的dmesg以获取更多信息。