Hi all
I recently setup a CentOS 5.2 server, running XEN (using HyperVM), and then moved the hard drive from my test box to my Intel server.The problem I now have, is that it doesn't bootup properly. Shortly after I see the udev service started, the machine reboots. This keeps on going the whole time.
I have managed to kill udev on start-up (with CTRL + C), and then it boots up. So, do I need udev? And what is it's purpose?
Rudi Ahlers schreef:
I have managed to kill udev on start-up (with CTRL + C), and then it boots up. So, do I need udev? And what is it's purpose?
Udev is a device probing layer. In the old days we had a /dev system prepped for standard use which would be complemented with other bootup scripts to make nodes for all hardware in your system.
Udev is the successor of this system (the one line history version anyway) and builds up the /dev folder with all your devices. In theory this is great but most systems (and I'm fairly sure CentOS as well) still have a number of base nodes in /dev before udev is fully started. This helps the system boot and in case of emergency (udev crashing or a broken probing like you have) this would allow the system to boot and find its primary devices (if you are lucky this might include all neccesary devices, in my case for example, when udev won't start I only have one of 2 SATA controllers online).
So in short, you might be able to turn off udev but adding new hardware, plugging in usb devices or similar or starting some non-standard hardware won't work any more. Perhaps there are more serious issues (like soft-raids ignoring the raid and just using one drive).
You might be able to see in the kernel console (ctrl+f10) what happens just before the system reboots - if it is a module which fails (most likely) you could blacklist it. That would solve the reboots. If the module is in fact critical for some piece of hardware you might be able to tweak it instead of disabling udev altogether.
Do the system logs contain any clues what is going on or does the system kills itself before logging to harddisc comes on?
Regards, Berend Dekens
On Mon, Nov 17, 2008 at 2:32 AM, Berend Dekens berend@cyberwizzard.nl wrote:
Rudi Ahlers schreef:
I have managed to kill udev on start-up (with CTRL + C), and then it boots up. So, do I need udev? And what is it's purpose?
Udev is a device probing layer. In the old days we had a /dev system prepped for standard use which would be complemented with other bootup scripts to make nodes for all hardware in your system.
Udev is the successor of this system (the one line history version anyway) and builds up the /dev folder with all your devices. In theory this is great but most systems (and I'm fairly sure CentOS as well) still have a number of base nodes in /dev before udev is fully started. This helps the system boot and in case of emergency (udev crashing or a broken probing like you have) this would allow the system to boot and find its primary devices (if you are lucky this might include all neccesary devices, in my case for example, when udev won't start I only have one of 2 SATA controllers online).
So in short, you might be able to turn off udev but adding new hardware, plugging in usb devices or similar or starting some non-standard hardware won't work any more. Perhaps there are more serious issues (like soft-raids ignoring the raid and just using one drive).
You might be able to see in the kernel console (ctrl+f10) what happens just before the system reboots - if it is a module which fails (most likely) you could blacklist it. That would solve the reboots. If the module is in fact critical for some piece of hardware you might be able to tweak it instead of disabling udev altogether.
Do the system logs contain any clues what is going on or does the system kills itself before logging to harddisc comes on?
Regards, Berend Dekens _______________________________________________
Hi Barend,
Thanx for the info :)
Unfortunately I don't see anything useful in the logs. If I let it bootup by itself, then it reboots just after booting udev. If, however, I press CTRL+C the moment I see udev on the screen, I have attached a snippet from /var/log/message - which doesn't show me anything at all.
Rudi Ahlers schreef:
Unfortunately I don't see anything useful in the logs. If I let it bootup by itself, then it reboots just after booting udev. If, however, I press CTRL+C the moment I see udev on the screen, I have attached a snippet from /var/log/message - which doesn't show me anything at all.
Indeed - I see some error messages about memory being assign to weird places and ata1 claiming to be a dummy... But nothing that should warrant something like a reboot...
I did however see some Xen messages. I am no expert so I can't see if this is a hypervisor kernel or a virtual machine kernel. If you are not planning on using the machine for or in an Xen environment, you could try to switch to a regular one (even if it is for testing). I have had some strange behaviour from systems which reacted poorly to virtualisation software (most of those get fixed but they can send you into the wrong direction).
Another thing that came to mind was that udev might finish properly but the next task might crash the system. I would however expect something in the message output. Did you check if the udev service claimed to be started if you ctrl+c out of it? Its unlikely but can't hurt to test.
If all else fails, you could probably disable udev for now and check if everything is working (make sure you don't need pluggable device support, otherwise you really do need udev). Plan B would be to Google for a debugging mode in udev - unless someone on the list knows how to activate that. My guess would be to edit the udev script and pass something to the program (most of the time its something like '-v' or '-vv' or '-d' or something - look for verbose or debug options).
Good luck, Berend
-
Berend Dekens -
Phil Schaffner -
Rudi Ahlers