Unix and Linux Stack Exchange
Unix and Linux Stack Exchange

Questions tagged [dmesg]

256 questions
226
votes
7 answers

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?
Milad Khajavi
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7 answers

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 this bus: [ziga@Ziga-PC ~]$ lsusb Bus 003 Device…
71GA
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4 answers

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 /var/log/dmesg.0, to see how my computer crashed.…
donquixote
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4 answers

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 of dmesg? More Info that may be helpful: - There…
xanpeng
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71
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6 answers

How can I write to dmesg from command line?

I'd like to write a statement to dmesg. How can I do this?
notlesh
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68
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1 answer

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: % cat /dev/kmsg cat: /dev/kmsg:…
malat
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43
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3 answers

Why is dmesg called dmesg?

Is there any explanation/history behind the name of the command dmesg (which prints out some kernel messages)?
imz -- Ivan Zakharyaschev
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31
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1 answer

What is the difference between dmesg and journalctl

I am completely new to Linux. I know that dmesg and journalctl record commands invoked by my operating-system, but why do 2 recorders exist, what types of messages should I expect to see within each of them, and what are the differences in their…
Rimski
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30
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3 answers

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 opened a new log file, /var/log/messages, with…
miluz
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23
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2 answers

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 promiscuous mode [ 18.750000] cfg80211: Calling CRDA for…
user55518
22
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3 answers

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\x2dgetty.slice. [633232.317222] serial8250: too…
Philipp Claßen
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20
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1 answer

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 about this message?
cjorssen
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14
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2 answers

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?
Ferroao
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13
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1 answer

How to read *.journal files?

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 a directory /var/log/journal. It has many files…
RatDon
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12
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1 answer

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 ... [ 95.709163] wlo1: associated [ 95.709218] IPv6:…
Philip Kirkbride
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