Questions tagged [dmesg]

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177
votes
7answers
197k views

How can I see dmesg output as it changes?

I'm writing a device driver that prints error message into ring buffer dmesg output. I want to see the output of dmesg as it changes. How can I do this?
67
votes
5answers
408k views

command to determine ports of a device (like /dev/ttyUSB0)

I have a question regarding the ports in Linux. If I connect my device via USB and want to check its port I can't do it using the command lsusb, which only specifies bus number and device number on ...
63
votes
4answers
171k views

What's the difference of dmesg output and /var/log/messages?

AFAIK dmesg shows information about kernel and kernel modules, and /var/log/messages also shows information produced by kernel and modules. So what's the difference? Does /var/log/messages ⊂ output ...
60
votes
5answers
45k views

How can I write to dmesg from command line?

I'd like to write a statement to dmesg. How can I do this?
50
votes
3answers
90k views

How to read dmesg from previous session? (dmesg.0)

dmesg is a command to read the contents from /var/log/dmesg. The nice thing compared to less /var/log/dmesg is that I can use the -T flag for human readable time output. Now I would like to look at /...
42
votes
3answers
5k views

Why is dmesg called dmesg?

Is there any explanation/history behind the name of the command dmesg (which prints out some kernel messages)?
26
votes
1answer
33k views

dmesg: read kernel buffer failed: Permission denied

Since recently Debian has changed the default behavior for dmesg and I cannot use it simply from my local user. % dmesg dmesg: read kernel buffer failed: Operation not permitted Same goes for: % ...
25
votes
3answers
78k views

How can dmesg content be logged into a file?

I'm running a Linux OS that was built from scratch. I'd like to save the kernel message buffer (dmesg) to a file that will remain persistent between reboots. I've tried running syslogd but it just ...
22
votes
2answers
28k views

Human readable dmesg time stamps on OpenWRT

The output of dmesg shows the number of second+milliseconds since the system start. [ 10.470000] ohci_hcd: USB 1.1 'Open' Host Controller (OHCI) Driver [ 14.610000] device eth0 entered ...
20
votes
3answers
24k views

Understanding “serial8250: too much work for irq4” kernel message

dmesg shows lots of messages from serial8250: $ dmesg | grep -i serial [ 0.884481] Serial: 8250/16550 driver, 32 ports, IRQ sharing enabled [ 6.584431] systemd[1]: Created slice system-serial\...
17
votes
1answer
9k views

What is the difference between dmesg and journalctl [closed]

I am completely new in Linux. What I see are two logs that run approximately in the same way. Why there are two logs? What kind of messages I expect to see in each of them? And what is the difference ...
11
votes
1answer
4k views

What is the first column in dmesg?

I'm trying the dmesg command which outputs the message buffer of the kernal. The format returned on my setup is in the format: ... [ 0.000000] 3 base 100000000 mask F00000000 write-back ... [ ...
11
votes
1answer
5k views

What does “usb: port power management may be unreliable” actually mean?

Trying to debug an issue with an ethernet usb-c adaptor, I found that dmesg reports this: usb: port power management may be unreliable What does this mean? Where can I find a reliable documentation ...
10
votes
1answer
6k views

Difference between output of dmesg and content of /var/log/dmesg?

I found the output of dmesg and content of /var/log/dmesg are different. Then what differences are between their purposes?
9
votes
3answers
4k views

decrease kernel boot log verbosity level

When my kernel boots, apart from the useful important information, it prints lots of debugging info, such as .... kernel: [0.00000] BIOS-e820: [mem 0x0000000000000000-0x000000000009d3ff] usable ...
9
votes
1answer
3k views

Where does the kernel ring buffer sit relative to rsyslog?

Is rsyslog just an abstraction layer on top of the kernel ring buffer? Or is the kernel ring buffer its own entity and rsyslogs interaction is like that of any other "application"?
8
votes
1answer
3k views

Do I need to take action regarding my Microarchitectural Data Sampling (MDS) status?

My dmesg output contains the following line: [ 0.265021] MDS CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/mds.html for more ...
7
votes
2answers
6k views

USB device messages flooding dmesg (and console)

When USB mouse is plugged into my laptop, dmesg is flooded with following messages: usb 3-1: USB disconnect, device number 28 usb 3-1: new low-speed USB device number 29 using xhci_hcd usb 3-1: New ...
7
votes
0answers
4k views

Linux 3.x fails assigning PCI BAR memory

I got an IBM x3850 type 8864 machine, I can successfully boot using a 2.6.32 kernel but when I try to use a 3.10 kernel or newer the kernel fails to initialize all PCI slots (I can fix this (manually),...
6
votes
1answer
23k views

How to know what to grep for in dmesg?

I recently had some trouble with a wireless card, and an online forum suggested searching dmesg with grep firmware. That helped, I was able to find the problem immediately! However, the previous hour ...
6
votes
1answer
15k views

How to filter the dmesg log to see only the errors

I am in ubuntu, when I write dmesg the error messages appear in red, how could I print in the console only those?
6
votes
3answers
2k views

“Calgary: Unable to locate Rio Grande table in EBDA” <- what does this mean?

When I boot my system, I get the following message: [Sat Oct 26 20:34:25 2019] Calgary: detecting Calgary via BIOS EBDA area [Sat Oct 26 20:34:25 2019] Calgary: Unable to locate Rio Grande table in ...
6
votes
2answers
11k views

Mount an USB: dmesg shows nothing

I'm trying to mount a USB-drive. However, it seems that my Linux (Debian) doesn't recognise it at all (and any other usb-drive), though it powers it. The usb-hubs are OK, because I was able to boot ...
6
votes
1answer
2k views

How to exclude auditd messages from dmesg and only log them in /var/log/audit.log

I use audit to log suspicious user actions on a workstation in my institution. I found that, in addition to logging to /var/log/audit.log, auditd also writes to /var/log/messages. Consequently, ...
6
votes
0answers
883 views

How hardware detection works in linux? [closed]

Whenever I have to troubleshoot "wifi is not working", "video is not working" etc. problems in linux I really do not understand how to do it correctly. My approach is messy: try lspci, look into dmesg,...
5
votes
3answers
2k views

dmesg with / without sudo on Debian / Mint

I noticed this difference some time ago, but until now, I didn't bother to ask, why is that? On Linux Mint 18 (Ubuntu-based) I can run dmesg without using sudo. On GNU/Linux Debian 9 I must use sudo ...
5
votes
2answers
6k views

How to print kernel time from command line?

How can I convert the uptime output to seconds since epoch to compare with dmesg output? Does uptime have the same resolution as the kernel message time? Is there a way to more directly get the ...
5
votes
2answers
359 views

dmesg: custom time format

dmesg has the option -T to print human-readable timestamps, and new versions have the option --time-format, where the time format can be changed, for instance: --time-format iso Unfortunately, the ...
5
votes
3answers
234 views

How do I troubleshoot some unexpected error messages reported while booting Debian 10?

I upgraded my Debian from 9th version to 10th when Debian 10 was officially released. Since I upgraded to Debian 10, I am getting following messages while booting: [ 11.008027] pstore: Using ...
5
votes
1answer
346 views

USB drive offline in dmesg and ? in ls, but only for some files?

I have a backup drive that has been intermittently failing (but almost always succeeding) to run rsnapshot lately. ls and e2label output are not encouraging: $ ls -al /mnt/backup/ ls: cannot access /...
4
votes
1answer
3k views

Remove ECC warnings in system log

How can I disable these warnings about ECC? I don't have ECC memory and so disabled it in bios also but it still prints it. [ 4.697057] EDAC amd64: Node 0: DRAM ECC disabled. [ 4.697061] EDAC ...
4
votes
1answer
7k views

“kernel: Buffer I/O error on device” - Does my server have a hardware problem?

we have linux DB server redhat 7.2 we notice about many message as below about all disks that are mounted from /var/log/messages what we are need to understand if this behavior is relevant to HW ...
4
votes
2answers
10k views

How can I activate extra-verbose mode (debugging mode) during Debian boot?

How do I activate extra verbosity during boot, on Debian? I removed the quiet parameter and tried to add debug but it didn't help. My problem is that my keyboard takes 2-3 min to activate so it ...
4
votes
1answer
16k views

enp3s0: link is not ready

I've some strange messages in the dmesg output: [ 7.588762] IPv6: ADDRCONF(NETDEV_UP): enp3s0: link is not ready [ 7.589616] IPv6: ADDRCONF(NETDEV_UP): enp3s0: link is not ready [ 7.591897] ...
4
votes
1answer
581 views

dmesg email digest

I have a remote server which has some issues (Seem hardware related) which means that it logs KVM errors and then sometime later it becomes unresponsive and locked up. There is an often an early ...
4
votes
2answers
2k views

Why and how to track /var/log/dmesg with version control

On this wiki they recommend tracking /var/log/dmesg using Mercurial. I wanted to set up a cron job on CentOS 6.4 like on this page to remind myself to make commit messages for such a repo. However, ...
4
votes
1answer
5k views

dmesg - “new high-speed USB device” repeated forever [closed]

I am on Debian Jessie 8.5 64bit on a VAIO laptop. If I run dmesg on my system, I get the following: [ 1031.025538] usb 1-1.2: new high-speed USB device number 62 using ehci-pci [ 1031.293612] usb 1-1....
4
votes
0answers
1k views

How to debug ACPI/poweroff problems?

I recently replaced my hard drive with a Sandisk SSD and did a fresh install of Fedora 21 (previously using F20). Now my laptop won't power off, and I'm not sure which of the two is causing the ...
4
votes
2answers
2k views

Slow root / mounting time

By running dmesg -t -d on my Raspbian/Debian Jessie, I see that this is a bottleneck in my booting process: [< 4.777880>] EXT4-fs (mmcblk0p2): mounted filesystem with ordered data mode. ...
3
votes
3answers
416 views

dmesg follow in FreeBSD

Is there a way to watch dmesg in realtime on FreeBSD like using the --follow (-w) option on dmesg in Linux?
3
votes
1answer
10k views

How to read *.journal files? [duplicate]

I want to see the previous dmesg log before the reboot. In previous versions of fedora, It used to be in /var/log/messages. But from Fedora 20, it's being stored through systemd i.e. journalctl. I've ...
3
votes
1answer
4k views

Is there a way to temporarily disable segfault messages in dmesg?

Linux kernel keeps logging segfaults in ring buffer. a.out[25415]: segfault at 8049604 ip 08049604 sp bf88e3fc error 15 in a.out[8049000+1000] Is there a way to temporarily disable it? My usecase ...
3
votes
1answer
2k views

dmesg + Assuming drive cache: write through

when we run the following dmesg on rhel 7.2 , we get errors about assuming drive cache dmesg --level=err [ 5.325381] sd 0:0:0:0: [sda] Assuming drive cache: write through [ 5.325492] sd 0:0:5:0:...
3
votes
1answer
3k views

Writing to /dev/kmsg randomly shows up in /proc/kmsg and always in dmesg?

When writing a message to /dev/kmsg while tailing /proc/kmsg the messages show up very randomly, in never shows up in /var/log/kern.log. However, dmesg gets all the messages correctly. Example # ...
3
votes
4answers
23k views

Log iptables events on centos 7

I have got iptables on my centos 7. My firewalld is disabled. How can I log my iptables events? On debian it is dmesg option but I don't know how to set it on centos. I want to log all of my iptables ...
3
votes
2answers
2k views

Interpreting output of dmesg and /var/log/boot.log

I found two ways for printing boot messages one using dmesg and another the content of file /var/log/boot.log: The content of the /var/log/boot.log file are: fsck from util-linux 2.20.1 /dev/loop0:...
3
votes
2answers
1k views

How can I find out what the entries in dmesg means?

It's interesting to look at the entries in dmesg, but how can I find out what they all mean? I did man dmesg, but I can't find anything about decoding the messages themselves. I wonder: Is there a ...
3
votes
1answer
97 views

What is the meaning of “Worm initializing…” in the output of dmesg?

I have an RHEL 5 system: [root@myhost ~]# cat /etc/redhat-release Red Hat Enterprise Linux Server release 5.11 (Tikanga) When I run dmesg, I get a strange and disconcerting message: [root@myhost ~]...
3
votes
1answer
531 views

What do the fields in the libata device probe line in dmesg mean?

When the kernel boots, it prints out lines like this for each SATA device: [ 0.919450] ata2.00: ATA-8: ST2000DM001-1CH164, CC24, max UDMA/133 [ 0.919487] ata2.00: 3907029168 sectors, multi 16: ...
3
votes
1answer
2k views

What is MCH_SSKPD warning in dmesg?

While i was reading dmesg log just to check that everything is fine, i met [ 18.956187] [drm] Wrong MCH_SSKPD value: 0x16040307 [ 18.956190] [drm] This can cause pipe underruns and display ...

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