Wednesday, July 20, 2011

dmesg(1) changes for util-linux 2.20

I have re-written the dmesg(1). That's the first large change in the code in last 18 years.

New features:
  • --decode facility and level number to human readable prefixes
$ dmesg --decode
kern  :info  : [26443.677632] ata1.00: configured for UDMA/100
kern  :info  : [26443.830225] PM: resume of devices complete after 2452.856 msecs
kern  :debug : [26443.830606] PM: Finishing wakeup.
kern  :warn  : [26443.830608] Restarting tasks ... done.
  • filter out messages according to the --facility and --level options, for example
$ dmesg --level=err,warn

$ dmesg --facility=daemon,user

$ dmesg --facility=daemon --level=debug

  • -u, --userspace to print only userspace messages

  • -k, --kernel to print only kernel messages

  • -t, --notime to skip [...] timestamps

  • -T, --ctime to print human readable timestamp in ctime()-like format. Unfortunately, this is useless on laptops if you have used suspend/resume. (The kernel does not use the standard system time as a source for printk() and it's not updated after resume.)

  • --show-delta to print time delta between printed messages
$ dmesg --show-delta
[35523.876281 <    4.016887>] usb 1-4.1: new low speed USB device using  hci_hcd and address 12
[35523.968398 <    0.092117>] usb 1-4.1: New USB device found, idVendor=413c, idProduct=2003
[35523.968408 <    0.000010>] usb 1-4.1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[35523.968416 <    0.000008>] usb 1-4.1: Product: Dell USB Keyboard

22 comments:

  1. Adam StokesJuly 20, 2011 at 7:10 PM

    That my friend, is awesome

    ReplyDelete
  2. ChrisJuly 20, 2011 at 9:12 PM

    AWESOME!

    ReplyDelete
  3. SEJeffJuly 20, 2011 at 11:15 PM

    Thanks for posting about this. Wow this is really sweet!

    ReplyDelete
  4. vendel.ínJuly 21, 2011 at 12:48 PM

    This comment has been removed by the author.

    ReplyDelete
  5. landtunaJuly 21, 2011 at 4:59 PM

    How about a tail -f functionality, so that it can follow new kernel messages?

    ReplyDelete
  6. Cyde WeysJuly 21, 2011 at 6:10 PM

    Landtuna, the UNIX philosophy is to do one thing and do it well. Tail -f already exists, so why duplicate that functionality in dmesg? You can always just do dmesg|tail -f

    ReplyDelete
  7. AnonymousJuly 21, 2011 at 7:14 PM

    Cyde, that won't work. tail -f works by checking the file constantly (or perhaps using one of the more recent APIs to have the kernel do the checking). dmesg is a program that spits out results and quits, there's nothing for tail -f to work with.

    (In general, it never makes sense to pipe into tail -f, only to run tail -f on a file(s).)

    ReplyDelete
  8. karelzakJuly 21, 2011 at 8:20 PM

    ad dmesg -f, this is already in util-linux TODO, but it's not so simple.

    http://www.spinics.net/lists/util-linux-ng/msg04491.html

    http://www.spinics.net/lists/util-linux-ng/msg04498.html

    We will see.

    ReplyDelete
  9. AnonymousJuly 22, 2011 at 1:07 AM

    Nice!

    ReplyDelete
  10. RobJuly 22, 2011 at 9:08 AM

    @Cyde Weys then why is he adding flags that we could just grep for, hmm?

    ReplyDelete
  11. AnonymousJuly 23, 2011 at 2:18 PM

    $ watch 'dmesg | tail'

    I usually resort to this... but tailing it properly would be nice.

    ReplyDelete
  12. AnonymousJuly 24, 2011 at 1:26 AM

    Thank you!

    ReplyDelete
  13. AnonymousJuly 24, 2011 at 5:31 PM

    This is great, thanks!

    ReplyDelete
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