[RFC] zero downtime upgrades to the kernel.

[RFC] zero downtime upgrades to the kernel.

[James Courtier-Dutton]

Has anyone investigated how one might be able to upgrade the linux 
kernel without rebooting?

We could maybe start with just being able to upgrade kernel modules 
while the modules were still in use.

E.g. There is a bug in the hard disc driver, and we have a fix, but 
don't want to reboot the machine.
Could we replace the hard disc driver while it was still being used, and 
keep mounted partitions?

James

Re: [RFC] zero downtime upgrades to the kernel.

[Jesper Juhl]

On Tue, 10 Aug 2004, James Courtier-Dutton wrote:

> Has anyone investigated how one might be able to upgrade the linux kernel
> without rebooting?
> 

This pops up now and again. 

I myself posted a mail with the same suggestion back in 1998 
http://uwsg.iu.edu/hypermail/linux/kernel/9808.1/1282.html . 
Colin Slater suggested it in 2001 
http://www.ussg.iu.edu/hypermail/linux/kernel/0107.1/0313.html and there 
are additional occourances of this in the archives as well...

--
Jesper Juhl

Re: [RFC] zero downtime upgrades to the kernel.

[James Courtier-Dutton]

Jesper Juhl wrote:
> On Tue, 10 Aug 2004, James Courtier-Dutton wrote:
> 
> 
>>Has anyone investigated how one might be able to upgrade the linux kernel
>>without rebooting?
>>
> 
> 
> This pops up now and again. 
> 
> I myself posted a mail with the same suggestion back in 1998 
> http://uwsg.iu.edu/hypermail/linux/kernel/9808.1/1282.html . 
> Colin Slater suggested it in 2001 
> http://www.ussg.iu.edu/hypermail/linux/kernel/0107.1/0313.html and there 
> are additional occourances of this in the archives as well...
> 
> --
> Jesper Juhl
> 

Thank you....stop this thread now. ;-)

Re: [RFC] zero downtime upgrades to the kernel.

[Helge Hafting]

James Courtier-Dutton wrote:

> Has anyone investigated how one might be able to upgrade the linux 
> kernel without rebooting?
>
> We could maybe start with just being able to upgrade kernel modules 
> while the modules were still in use.
>
> E.g. There is a bug in the hard disc driver, and we have a fix, but 
> don't want to reboot the machine.
> Could we replace the hard disc driver while it was still being used, 
> and keep mounted partitions?

You can only upgrade a module that isn't in use.  So, umount everything 
using that
driver (keeping linux running from some other drive (or ramdisk)) 
replace module,
reload module, remount filesystems.  This can be quite fast, but you do 
have to
umount (and stop all the processes running from those disks.)


There are some trick you can use with disks:
1. Have root on a initial ramdisk, and never remount to a real disk.  
This way,
    all disks can be umounted so any disk device driver can be 
replaced.  You'll
    tie up a fair amount of memory in that big initial ramdisk though.

2. Consider using multipath and different scsi adapters using different 
drivers.
   Perhaps this will let you unload adapter drivers one at a time while you
   reload the other one, and keeps disks & processes running troughout.

3. Have two identical pc's sharing a set of scsi equipment.  When you 
want to upgrade
the base kernel on one, set your IP addressses so traffic goes to the other.
This should work with protocols that allows server reboot, such as nfs.

You simply won't get a linux kernel (or module) that can be replaced 
while running,
but redundant hardware may give some of the same benefits.

Helge Hafting