Linux系統中『dmesg』命令處理故障和收集系統信息的7種用法
『dmesg』命令顯示linux內核的環形緩衝區信息,我們可以從中獲得諸如系統架構、cpu、掛載的硬體,RAM等多個運行級別的大量的系統信息。當計算機啟動時,系統內核(操作系統的核心部分)將會被載入到內存中。在載入的過程中會顯示很多的信息,在這些信息中我們可以看到內核檢測硬體設備。
『dmesg』命令設備故障的診斷是非常重要的。在『dmesg』命令的幫助下進行硬體的連接或斷開連接操作時,我們可以看到硬體的檢測或者斷開連接的信息。『dmesg』命令在多數基於Linux和Unix的操作系統中都可以使用。
下面我們展示一些最負盛名的『dmesg』命令工具以及其實際使用舉例。『dmesg』命令的使用語法如下。
# dmesg [options...]
1. 列出載入到內核中的所有驅動
我們可以使用如『more』。 『tail』, 『less 』或者『grep』文字處理工具來處理『dmesg』命令的輸出。由於dmesg日誌的輸出不適合在一頁中完全顯示,因此我們使用管道(pipe)將其輸出送到more或者less命令單頁顯示。
[root@tecmint.com ~]# dmesg | more
[root@tecmint.com ~]# dmesg | less
輸出
[ 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. 列出所有被檢測到的硬體
要顯示所有被內核檢測到的硬碟設備,你可以使用『grep』命令搜索『sda』關鍵詞,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)
註解 『sda』表示第一塊 SATA硬碟,『sdb』表示第二塊SATA硬碟。若想查看IDE硬碟搜索『hda』或『hdb』關鍵詞。
3. 只輸出dmesg命令的前20行日誌
在『dmesg』命令後跟隨『head』命令來顯示開始幾行,『dmesg | head -20′命令將顯示開始的前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. 只輸出dmesg命令最後20行日誌
在『dmesg』命令後跟隨『tail』命令(『 dmesg | tail -20』)來輸出『dmesg』命令的最後20行日誌,當你插入可移動設備時它是非常有用的。
[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
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. 搜索包含特定字元串的被檢測到的硬體
由於『dmesg』命令的輸出實在太長了,在其中搜索某個特定的字元串是非常困難的。因此,有必要過濾出一些包含『usb』 『dma』 『tty』 『memory』等字元串的日誌行。grep 命令 的『-i』選項表示忽略大小寫。
[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
輸出
[ 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緩衝區日誌
我們可以使用如下命令來清空dmesg的日誌。該命令會清空dmesg環形緩衝區中的日誌。但是你依然可以查看存儲在『/var/log/dmesg』文件中的日誌。你連接任何的設備都會產生dmesg日誌輸出。
[root@tecmint.com log]# dmesg -c
7. 實時監控dmesg日誌輸出
在某些發行版中可以使用命令『tail -f /var/log/dmesg』來實時監控dmesg的日誌輸出。
[root@tecmint.com log]# watch "dmesg | tail -20"
結論:dmesg命令在系統dmesg記錄實時更改或產生的情況下是非常有用的。你可以使用man dmesg來獲取更多關於dmesg的信息。
Narad Shrestha
他在IT領域擁有超過10年的豐富經驗,其中包括各種Linux發行版,開源軟體和網路工作。 Narad始終堅持與他人分享IT知識和自如地運用新技術。
via: http://www.tecmint.com/dmesg-commands/
本文轉載來自 Linux 中國: https://github.com/Linux-CN/archive