How do I convert dmesg timestamp to custom date format

Question

I am trying to understand the dmesg timestamp and find it hard to convert that to change it to java date custom date format  Sample dmesg log   14614 647880  airo eth1   link lost  missed beacons   So how do I convert 14614 647880 to a standard date

User · Accepted Answer

Understanding dmesg timestamp is pretty simple  it is time in seconds since the kernel started  So  having time of startup  uptime   you can add up the seconds and show them in whatever format you like   Or better  you could use the -T command line option of dmesg and parse the human readable format   From the man page   -T  --ctime     Print human readable timestamps  The timestamp could be inaccurate       The time source used for the logs is not updated after system SUSPEND RESUME

User · Answer

With the help of dr answer  I wrote a workaround that makes the conversion to put in your  bashrc  It won t break anything if you don t have any timestamp or already correct timestamps   dmesg with human timestamps            type -P dmesg         perl -w -e  use strict          my   uptime    do   local  ARGV   proc uptime   lt  gt      uptime      uptime        d                foreach my  line   lt  gt                 printf    line       s   d     d                 s  s n   scalar localtime time -  uptime    1    2      line                alias dmesg dmesg with human timestamps   Also  a good reading on the dmesg timestamp conversion logic  amp  how to enable timestamps when there are none  https   supportcenter checkpoint com supportcenter portal eventSubmit doGoviewsolutiondetails  amp solutionid sk92677

User · Answer

For systems without  dmesg -T  such as RHEL CentOS 6  I liked the  dmesg with human timestamps  function provided by lucas-cimon earlier  It has a bit of trouble with some of our boxes with large uptime though  Turns out that kernel timestamps in dmesg are derived from an uptime value kept by individual CPUs  Over time this gets out of sync with the real time clock  As a result  the most accurate conversion for recent dmesg entries will be based on the CPU clock rather than  proc uptime  For example  on a particular CentOS 6 6 box here     grep    clock   proc sched debug    head -1    clock                           32103895072 444568   uptime  15 54 05 up 371 days  19 09   4 users   load average  3 41  3 62  3 57   cat  proc uptime 32123362 57 638648955 00   Accounting for the CPU uptime being in milliseconds  there s an offset of nearly 5 1 2 hours here  So I revised the script and converted it to native bash in the process   dmesg with human timestamps          FORMAT   a  b  d  H  M  S  Y       now   date   s      cputime line   grep -m1    clock   proc sched debug       if     cputime line      0-9    0-9          then         cputime    BASH REMATCH 1    1000       fi      dmesg   while IFS  read -r line  do         if     line            0-9      0-9               then             stamp    now-cputime BASH REMATCH 1                echo     date     FORMAT   --date    stamp      BASH REMATCH 2            else             echo   line          fi     done    alias dmesgt dmesg with human timestamps

User · Answer

So KevZero requested a less kludgy solution  so I came up with the following   sed -r  s      0-9     0-9          echo -n     echo -n   date --date     echo    grep btime  proc stat cut -d     -f 2   1    bc      c   echo -n     echo -n   2  e    Here s an example     dmesg tail   sed -r  s      0-9     0-9          echo -n     echo -n   date --date     echo    grep btime  proc stat cut -d     -f 2   1    bc      c   echo -n     echo -n   2  e   2015-12-09T04 29 20 COT  cfg80211     57240000 KHz - 63720000 KHz   2160000 KHz    N A  0 mBm    N A   2015-12-09T04 29 23 COT  wlp3s0  authenticate with dc 9f db 92 d3 07  2015-12-09T04 29 23 COT  wlp3s0  send auth to dc 9f db 92 d3 07  try 1 3   2015-12-09T04 29 23 COT  wlp3s0  authenticated  2015-12-09T04 29 23 COT  wlp3s0  associate with dc 9f db 92 d3 07  try 1 3   2015-12-09T04 29 23 COT  wlp3s0  RX AssocResp from dc 9f db 92 d3 07  capab 0x431 status 0 aid 6   2015-12-09T04 29 23 COT  wlp3s0  associated  2015-12-09T04 29 56 COT  thinkpad acpi  EC reports that Thermal Table has changed  2015-12-09T04 29 59 COT  i915 0000 00 02 0  BAR 6       0x00000000 flags 0x2  has bogus alignment  2015-12-09T05 00 52 COT  thinkpad acpi  EC reports that Thermal Table has changed   If you want it to perform a bit better  put the timestamp from proc into a variable instead

User · Answer

you will need to reference the  btime  in  proc stat  which is the Unix epoch time when the system was latest booted  Then you could base on that system boot time and then add on the elapsed seconds given in dmesg to calculate timestamp for each events

User · Answer

If you don t have the -T option for dmesg as for example on Andoid  you can use the busybox version  The following solves also some other issues    The  0 0000  format is preceded by something that looks like misplaced color information  prefixes like  lt 6 gt    Make integers from floats    It is inspired by this blog post      bin sh                                                                                                                  Translate dmesg timestamps to human readable format                                                                       uptime in seconds                                                                                                      uptime   cut -d     -f 1  proc uptime                                                                                       remove fraction                                                                                                        uptime   echo  uptime   cut -d     -f1                                                                                      run only if timestamps are enabled                                                                                     if    Y       cat  sys module printk parameters time      then                                                             dmesg   sed  s                 sed  s             0-9                 1   2     while read timestamp message  do           timestamp   echo  timestamp   cut -d     -f1                                                                             ts1       busybox date   s  -  uptime    timestamp                                                                       ts2   busybox date -d     ts1                                                                                            printf    s   s n    ts2    message                                                                                    done                                                                                                                   else                                                                                                                       echo  Timestamps are disabled   sys module printk parameters time                                                      fi                                                                                                                         Note  however  that this implementation is quite slow

User · Answer

A caveat which the other answers don t seem to mention is that the time which is shown by dmesg doesn t take into account any sleep suspend time  So there are cases where the usual answer of using dmesg -T doesn t work  and shows a completely wrong time  A workaround for such situations is to write something to the kernel log at a known time and then use that entry as a reference to calculate the other times  Obviously  it will only work for times after the last suspend  So to display the correct time for recent entries on machines which may have been suspended since their last boot  use something like this from my other answer here    write current time to kernel ring buffer so it appears in dmesg output echo  quot timecheck    date   s      date   F  T  quot    sudo tee  dev kmsg    use our  quot timecheck quot  entry to get the difference   between the dmesg timestamp and real time offset   dmesg   grep timecheck   tail -1     perl -nle    t1  t2       d   S  timecheck    d     print  t2- t1      pipe dmesg output through a Perl snippet to   convert it s timestamp to correct readable times dmesg   tail     perl -pe  BEGIN  offset shift  s      d   S  localtime  1  offset  e   offset

User · Answer

In recent versions of dmesg  you can just call dmesg -T

User · Answer

With older Linux distros yet another option is to use wrapping script  e g  in Perl or Python    See solutions here   http   linuxaria com article how-to-make-dmesg-timestamp-human-readable lang en http   jmorano moretrix com 2012 03 dmesg-human-readable-timestamps

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