Comment # 12 on bug 917411 from Takashi Iwai

(In reply to macias - from comment #10)
> I am sorry, but I have to reopen it, because the system keeps freezing. What
> I found out so far:
> * the old kernel also freezes

OK, this is very good to know at least.
Did you have a working kernel beforehand?

> * journalctl does not show any error or trace of problem, simply there is no
> messages during "freeze" period (until hard reset, reboot is recorded, but
> this message could come from next boot)

As mentioned, here we need to know how "hard" the freeze is.

> > For example, if the
> > machine doesn't respond to network ping, it's likely a complete
> > freeze.
> 
> Ok, I do it next time.
> 
> > and the remote login still works.  
> 
> Errm, I would not like to open remote loging, because the freeze is not that
> often.

I didn't ask to keep opening the remote session.  Instead, just try remote
login when the machine hangs.

> > In the case of complete freeze, usually it's a kernel panic, and
> > the kernel always tries to leave some dying messages. 
> 
> Where? journalctl does not show anything related.

It's usually in journal.  In a better case, you could get via serial console. 
Or, even via netconsole, sometimes.

(In reply to macias - from comment #11)
> PS. When you write about SysRq you have console in mind? Because without
> freeze I tested out those shortcuts, and they work in console, but NOT in
> GUI desktop. SysRq is commented out by default, so there is no such key at
> all:
> 
> https://github.com/xkbcommon/libxkbcommon/blob/master/test/data/keycodes/
> evdev
> 
> And when system freezes I cannot switch to console.

I guess you misunderstood SysRq.  What's here referred to is the "Magic SysRq"
keys.  The key combo Alt+SysRq+something (on a laptop, it's often with
Alt+Fn+Print+something) is captured directly by kernel for special tasks.  So
it must work no matter which desktop GUI is used.

Note that not all sysrq key combos are enabled as default, as already
mentioned.  This has to be enabled via sysctl.conf stuff.

BTW, are you using BTRFS?  If so, is the disk space still really free?
A frequent seen problem with btrfs is that snapshots exhaust the free disk
space without noticing.  This leads to the system crash, and you won't see
always the log because it can't write more.  Try to remove old snapshots in the
case of btrfs, to be sure.

In anwyay, please clear NEEDINFO once when you get more information.