Could anyone explain what happens in system after unplugging CD-ROM during working with LiveCD session?
Suppose that I'm using Ubuntu LiveCD and suddenly by accident the CD-ROM disconnect for a matter of second because of for example power outage in the case of external devices or just opening the CD tray if the OS allows to do it. Assume that after a while the CD-ROM is pluged in again.
Can anyone explain what exactly happens then, why the OS stops or rather is working but not as before it and how, if it's possible, the stability and usefullness can be brought back and user can continue working with?
According to my observations based on Ubuntu LiveCDs (versions under 12, the kernel version is probably 2.6.XX) the system reaction is like following:
- all applications in X desktop disappear (I think it's due to automatic sending a kill signal to all processes as if the OS wanted to shut down but actually it seems to wait for something) and it looks like only the background image with the cursor which can be moved all the time
- all TTYs are avaible and can be displayed but there are only error messages there like
INFO: task <process name>:<pid> blocked for more than 120 secondsand
SquashFS error: unable to read [...]
- all the time I can see blinking '_' and I can type something but pressing enter just make it skipped to the new line and obviously the OS doesn't execute it
- terminal's shortcuts for canceling and quit current process also don't work
- magic SysRq combinations are generally working and I can see the actual output but I don't know which of them would be useful in this case
Can anyone explain this reaction and tell what exactly these errors mean? And what can one do then to fix it - is there any way for that and why not, if so?
Here: http://unix.stackexchange.com/questions/76166/what-does-info-task-xxx-blocked-for-more-than-120-seconds-exactly-mean-on-lin I've just read that "if a task is blocked, it waits for resources to become available again". So if I got it correctly it's waiting for resources - is it true or just wrong interpretation and it will wait endlessly - CD-ROM is surely pluged in again as fast as possible. How to understand it?
I know that processes are gone (or "blocked" as error messages are suggesting?), but how about files in the ramdisk, are they still there untill reboot? Is this possible to access them somehow? Or for example just extract text strings and so on?
There is a magic SysRq shourtcut which remount filesystems - are there any chances that it would help in such situations or should be tried eventually at the end after other trials? If the CD are working as virtual fs, what effects can bring remountig filesystems in that case?