How VPS - How to use/setup VPS
  • Home
  • Management guides
    • Web servers software
      • Directadmin
      • Hocvps Script
      • Centmin Mod
      • CWP
      • Kloxo-MR
      • Plesk
    • Control Panels
    • Securing VPS/Servers
      • SSL Certificates
      • Upgrading
      • Authentication
  • Operating System
    • CentOS
    • Fedora
    • Debian
    • Linux
    • Arch
    • BSD
    • CoreOS
  • Reviews
  • Coupon
    • Domain Coupon
    • Hosting Coupon
No Result
View All Result
  • Home
  • Management guides
    • Web servers software
      • Directadmin
      • Hocvps Script
      • Centmin Mod
      • CWP
      • Kloxo-MR
      • Plesk
    • Control Panels
    • Securing VPS/Servers
      • SSL Certificates
      • Upgrading
      • Authentication
  • Operating System
    • CentOS
    • Fedora
    • Debian
    • Linux
    • Arch
    • BSD
    • CoreOS
  • Reviews
  • Coupon
    • Domain Coupon
    • Hosting Coupon
No Result
View All Result
How VPS - How to use/setup VPS
No Result
View All Result
Home Operating System Linux

7 ‘dmesg’ Commands for Troubleshooting and Collecting Information of Linux Systems

How VPS by How VPS
November 2, 2018
in Linux, Operating System
0
0
SHARES
48
VIEWS
Share on FacebookShare on Twitter

Contents

  1. 1. List all loaded Drivers in Kernel
    1. Sample Output
  2. 2. List all Detected Devices
  3. 3. Print Only First 20 Lines of Output
  4. 4. Print Only Last 20 Lines of Output
  5. 5. Search Detected Device or Particular String
    1. Sample Output
  6. 6. Clear dmesg Buffer Logs
  7. 7. Monitoring dmesg in Real Time

The ‘dmesg‘ command displays the messages from the kernel ring buffer. A system passes multiple runlevel from where we can get lot of information like system architecture, cpu, attached device, RAM etc. When computer boots up, a kernel (core of an operating system) is loaded into memory. During that period number of messages are being displayed where we can see hardware devices detected by kernel.

Read Also: 10 Linux Commands to Collect System and Hardware Information

7 ‘dmesg’ Commands for Troubleshooting and Collecting Information of Linux Systems

dmesg Command Examples

The messages are very important in terms of diagnosing purpose in case of device failure. When we connect or disconnect hardware device on the system, with the help of dmesg command we come to know detected or disconnected information on the fly. The dmesg command is available on most Linux and Unix based Operating System.

Let’s throw some light on most famous tool called ‘dmesg’ command with their practical examples as discussed below. The exact syntax of dmesg as follows.

# dmseg [options...]

1. List all loaded Drivers in Kernel

We can use text-manipulation tools i.e. ‘more‘, ‘tail‘, ‘less‘ or ‘grep‘ with dmesg command. As output of dmesg log won’t fit on a single page, using dmesg with pipe more or less command will display logs in a single page.

[[email protected] ~]# dmesg | more
[[email protected] ~]# dmesg | less
Sample Output
[    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 ([email protected]) (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
.....

Read Also: Manage Linux Files Effectively using commands head, tail and cat

2. List all Detected Devices

To discover which hard disks has been detected by kernel, you can search for the keyword “sda” along with “grep” like shown below.

[[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)

NOTE: The ‘sda’ first SATA hard drive, ‘sdb’ is the second SATA hard drive and so on. Search with ‘hda’ or ‘hdb’ in the case of IDE hard drive.

3. Print Only First 20 Lines of Output

The ‘head’ along with dmesg will show starting lines i.e. ‘dmesg | head -20’ will print only 20 lines from the starting point.

[[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 ([email protected]) (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. Print Only Last 20 Lines of Output

The ‘tail’ along with dmesg command will print only 20 last lines, this is useful in case we insert removable device.

[[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. Search Detected Device or Particular String

It’s difficult to search particular string due to length of dmesg output. So, filter the lines with are having string like ‘usb‘ ‘dma‘ ‘tty‘ and ‘memory‘ etc. The ‘-i’ option instruct to grep command to ignore the case (upper or lower case letters).

[[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
Sample Output
[    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. Clear dmesg Buffer Logs

Yes, we can clear dmesg logs if required with below command. It will clear dmesg ring buffer message logs till you executed the command below. Still you can view logs stored in ‘/var/log/dmesg‘ files. If you connect any device will generate dmesg output.

[[email protected] log]# dmesg -c

7. Monitoring dmesg in Real Time

Some distro allows command ‘tail -f /var/log/dmesg’ as well for real time dmesg monitoring.

[[email protected] log]# watch "dmesg | tail -20"

Conclusion: The dmesg command is useful as dmesg records all the system changes done or occur in real time. As always you can man dmesg to get more information.

Source: tecmint.com

Tags: Linux Commandslinux guidelinux vps setup guide
How VPS

How VPS

Related Posts

Failed to download metadata for repo 'appstream' on Centos 8
CentOS

How to fix error: Failed to download metadata for repo ‘appstream’ on Centos 8

February 25, 2022
How to Install Apache Tomcat 8 on CentOS 7
Linux

How to Install Apache Tomcat 8 on CentOS 7?

February 11, 2020
Install Arch Linux With Btrfs Snapshotting
Uncategorized

Install Arch Linux With Btrfs Snapshotting

February 13, 2020
Next Post

The Silver Searcher – A Code Searching Tool for Programmers

How Do I Access or Mount Windows/USB NTFS Partition in RHEL/CentOS/Fedora

How to Enable Syntax Highlighting in Vi/Vim Editor

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Follow Us

  • 121 Followers
  • 87.2k Followers

Recommended

How to Install Automad CMS on Debian 9

3 years ago

How to Control Systemd Services on Remote Linux Server

4 years ago

How to Setup a Leanote Server on CentOS 7

3 years ago

How to Install Microweber on CentOS 7

3 years ago

Instagram

    Please install/update and activate JNews Instagram plugin.

Categories

  • Arch
  • Authentication
  • Backups
  • BSD
  • Centmin Mod
  • CentOS
  • Control Panels
  • CoreOS
  • CWP
  • Debian
  • Directadmin
  • Encryption
  • Fedora
  • Firewalls
  • Hocvps Script
  • Hosting providers
  • Kloxo-MR
  • Linux
  • Mitigations
  • Operating System
  • Plesk
  • Reviews
  • Securing VPS/Servers
  • Security Patches
  • SSL Certificates
  • Uncategorized
  • Upgrading
  • VPS/Servers management guides
  • Vulnerability Detection
  • Web servers software
  • Webhosting Control Panel

Topics

Apache Web Server Bluehost Review 2019 Bluehost Review 2020 Bluehost Review 2021 Centmin Mod CentminMod centos install htop fsck htop install HTTP DoS attack Install Snort on an Ubuntu install Zabbix on CentOS install Zabbix on CentOS 7 Linux Commands linux guide linux install htop linux vps setup guide MariaDB MariaDB Error Mysql mysqld error optimize MariaDB optimize Mysql snort Ubuntu
No Result
View All Result

Highlights

Top Free Web Hosting Control Panels To Manage VPS/Dedicated Servers

Webmin Reviews

Virtualmin Reviews

CentOS Web Panel Reviews

Ajenti Reviews

ISPConfig Reviews

Trending

Failed to download metadata for repo 'appstream' on Centos 8
CentOS

How to fix error: Failed to download metadata for repo ‘appstream’ on Centos 8

by How VPS
February 25, 2022
0

I tried to update some extensions by use yum on centOs which I specified in Dockerfile. After...

How to Fix MySQL Error "Plugin 'InnoDB' registration as a STORAGE ENGINE failed"?

How to Fix MySQL Error “Plugin ‘InnoDB’ registration as a STORAGE ENGINE failed”?

November 17, 2020
How to optimize Mysql or MariaDB

How to optimize Mysql or MariaDB

November 3, 2020
Top Free Web Hosting Control Panels To Manage VPS/Dedicated Servers

Top Free Web Hosting Control Panels To Manage VPS/Dedicated Servers

February 17, 2020
Webmin Reviews

Webmin Reviews

February 17, 2020
How VPS – How to use/setup VPS

We bring you the best Premium WordPress Themes that perfect for news, magazine, personal blog, etc. Visit our landing page to see all features & demos.
LEARN MORE »

Recent News

  • How to fix error: Failed to download metadata for repo ‘appstream’ on Centos 8 February 25, 2022
  • How to Fix MySQL Error “Plugin ‘InnoDB’ registration as a STORAGE ENGINE failed”? November 17, 2020
  • How to optimize Mysql or MariaDB November 3, 2020

Categories

  • Arch
  • Authentication
  • Backups
  • BSD
  • Centmin Mod
  • CentOS
  • Control Panels
  • CoreOS
  • CWP
  • Debian
  • Directadmin
  • Encryption
  • Fedora
  • Firewalls
  • Hocvps Script
  • Hosting providers
  • Kloxo-MR
  • Linux
  • Mitigations
  • Operating System
  • Plesk
  • Reviews
  • Securing VPS/Servers
  • Security Patches
  • SSL Certificates
  • Uncategorized
  • Upgrading
  • VPS/Servers management guides
  • Vulnerability Detection
  • Web servers software
  • Webhosting Control Panel

[mc4wp_form]

© 2018 JNews - City News Magazine WordPress theme. All rights belong to their respective owners.
JNews is a top selling 2018 WordPress News, Blog, Newspaper & Magazine Theme.

No Result
View All Result
  • Home

© 2023 JNews - Premium WordPress news & magazine theme by Jegtheme.