[mythtv-users] CTRL-ALT-BACKSPACE

Stephen Worthington stephen_agent at jsw.gen.nz
Fri Mar 8 16:53:54 UTC 2019


On Fri, 8 Mar 2019 07:17:37 -0800, you wrote:

>On Fri, Mar 8, 2019 at 3:16 AM Stephen Worthington <stephen_agent at jsw.gen.nz>
>wrote:
>
>> On Thu, 7 Mar 2019 22:45:16 -0800, you wrote:
>>
>> >I upgraded from Mythbuntu8 to mythbuntu18. X just froze and we used to use
>> >CTRL-ALT-BS but I know it has been removed.
>> >
>> >I have been Googling this and found that this was replaced by
>> >AysRq-rightAlt-K but that doesn't work. Then I found a nice gui checkbox
>> >that restored it but that isn't there.  I found several different files I
>> >could create, all different, and the instructions below that look like
>> they
>> >might work but I don't want to blow up the system so can someone tell me
>> if
>> >this is correct for Mythbuntu 18? (I modified it slightly to use nano).
>> >Basically I found almost a dozen ways to enable this in xfce but they were
>> >all different.  In the past very bad things happened when I just followed
>> >online instructions.  That is why I am asking for help
>> >
>> >Thanks,
>> >
>> >Allen
>> >
>> >Enable the key combination Ctrl+Alt+Backspace
>> >
>> >   1.
>> >
>> >   Open the Terminal and run sudo nano /etc/default/keyboard
>> >   2.
>> >
>> >   Find the line:
>> >   XKBOPTIONS=""
>> >   3.
>> >
>> >   Replace it with:
>> >   XKBOPTIONS="terminate:ctrl_alt_bksp"
>> >   4.
>> >
>> >   Save the modified file and close it.
>> >   5.
>> >
>> >   Reboot your computer to take affect.
>>
>> If you are using lightdm (as I do with Xubuntu 18), then log in from a
>> terminal (Alt-F1) or ssh and do "sudo systemctl restart lightdm" to
>> restart X.  That works pretty well for me, so I did not investigate
>> any further the various keystroke options.
>>
>> Thank you for the suggestion but it doesn't solve the problem.
>
>While the lightdm command worked on a test this morning, the system was not
>hung up so not sure if it would have worked last night.
>
>The issue last night was that Myth was frozen and the cursor was off.  In
>spite of no cursor, I was able to open system logoff command and click
>Logoff but Myth would not close and prevented X from closing.  The logoff
>attempt was met with a message "Myth is not responding do you want force a
>close, Y/N" or something like that but it did not respond to a "Y" from the
>keyboard so I was unable to logoff and had to use the power button.  The
>power button did not fully turn off the computer and I had to do a long
>press to force the computer to shut off.  Basically a hot mess. With
>Mythbuntu-8 this would happen one or two times a year and the simple key
>sequence would restart X and all was good.  My wife could do it without
>calling me down to issue some system commands.

That sounds like just a mythfrontend lockup, rather than X locking up
completely.  If you already have a window running a terminal in the
background when it happens, you should be able to just do Alt-Tab as
many times as necessary to get to that terminal.  Then from there do:

ps -e | grep mythfrontend

to find the PID for mythfrontend (or mythfrontend.real if it is
Ubuntu).  Then kill that process:

sudo kill <pid>

You usually need to do that command twice to actually kill
mythfrontend.  Or if mythfrontend is completely locked up, then you
may need to use:

sudo kill -9 <pid>

If you are running the XFCE desktop (Xubuntu), then you should also be
able to do Ctrl-Esc to bring up a menu where you can run a terminal
window from, or Ctrl-Alt-T to open a terminal window.  Or you can use
Ctrl-Alt-F1 to open a terminal directly in full screen mode.

WARNING: After a bad shutdown like using the power off button or after
a power failure, you need to check all your filesystems on all
partitions - there is a reasonable chance that any filesystem that had
a write in progress at the time of the shutdown will be corrupt
somewhere.  The fsck checks done automatically at boot time will
likely not find and fix such corruption.  You must a full "fsck -C -f
/dev/<partition id>" on all partitions that were mounted at the time,
and then that should fix any errors.  If you see any errors that
needed fixing, then run the command again on that partition as many
times as necessary until it runs without any errors to be fixed.
Failing to do this allows the corruption of the filesystem to remain
in place, and if any writes take place to corrupt files or corrupt
filesystem tables, then the corruption will likely spread and make the
partition unusable and unfixable - you can lose your entire system.

You can do fsck repairs like this by booting from a live DVD or live
USB, or from another bootable partition that has the same or later
version of the filesystem drivers and fsck programs.  I do this by
having a second bootable partition on my SSD, which has a script to do
all the fsck commands.  Booting from the normal boot partition in
repair mode is not able to do an fsck on the boot partition itself,
but can be used once the boot partition has been fixed to run fsck on
all the other partitions.

After you have clean filesystems, you then need to do a full check and
repair on the mythconverg database.  If it was being written to at the
time of the bad shutdown, any tables that were being modified at the
time may be crashed.  If a recording was in progress, typically the
recordedseek table will be crashed.  Unfortunately, when mythbackend
tries to record and it then writes to recordedseek, if the table is
crashed, all you get is some error messages in the mythbackend.log
file.  It appears that mythbackend is recording happily, when all the
time the writes to recordedseek are failing.  This does not stop a
recording from succeeding, but on playback there will be problems.  It
is possible to fix recordedseek, then use the "mythcommflag --rebuild"
command to add the correct recordedseek table entries for a recording
where this happens, but it is much better to fix the database before
that.  And if any table other than recordedseek is crashed, the
consequences are usually worse - if you write to other crashed tables,
you can corrupt the table completely to where it is unrepairable, and
that can mean you lose the entire database.  Fortunately, crashes of
other tables are rare.  To check and repair the database, run the
optimize_mythdb script.  It is here in Ubuntu:

/usr/share/doc/mythtv-backend/contrib/maintenance/optimize_mythdb.pl

That script should also be being run from /etc/cron.daily to prevent
any problems with database corruption.  Database corruption does
happen occasionally due to minor software bugs, and unless you are
running optimize_mythdb regularly to fix that corruption, it can and
usually will spread and eat your database.

>Even if that worked, CTRL-ALT-Backspace is a lot easier to use.  By the
>way, Alt-F1 does not bring up a terminal window on my system for some
>reason.

Sorry, I mis-typed that.  It is Ctrl-Alt-F1 for a terminal.

>What I need is something like CTRL-ALT-Backspace, or the SysRq-Alt-K (which
>did not work) so that my wife can restart X.  While I appreciate knowing
>about the systemctl command, it is not "wife friendly" at least in the case
>of my wife. The power button would be an option but it interrupts
>recordings and even it didn't really work last night,  I needed the long
>press.

The power button is not a good option at all, due to the possible loss
of files, whole partitions, the database, or the entire system.  It
should only be used as a last resort, and must be followed by the full
check and fix procedure as above.

>Allen


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