Ok, it is quite simple with grub.

For instance, with a debian jessie:

1. install ipxe with grub

apt-get install ipxe

2. Set the next grub boot to use the ipxe menu

grub-reboot 2

3. Reboot !

reboot

The number to use is the number of the grub entry (counting the submenu) of the pxe entry, starting from 0.

Thank you for your help, I hope the result could help someone in the future.

Ok, it is quite simple with grub.

For instance, with a debian jessie:

1. install ipxe with grub

apt-get install ipxe

2. Set the next grub boot to use the ipxe menu

grub-reboot 2

3. Reboot !

reboot

The number to use is the number of the grub entry (counting the submenu) of the pxe entry, starting from 0.

Thank you for your help, I hope the result could help someone in the future.

@Junkhacker that is equivalent to the grub + ipxe solution I think, and I don’t have to insert a CD in all my machines at least
My absolute restriction is that I don’t have a physical access to each machine, only a root ssh access.

Or maybe you know a way to directly reboot to an iso located on a hard drive ?

@Junkhacker not every bios supports pxe unfortunately.

I am currently trying with grub and booting to ipxe, I’ll see what result it gives me.

@Wayne-Workman I can go to a single machine, but not 200 of them in a reasonable time

@Wayne-Workman yes I have root ssh access. And you have expressed my request much better than me, thanks a lot.

No, I am not rebooting the client if using kexec, just replacing the current kernel with the kernel from the fog server.
It looks like a reboot, but it is not a reboot

Let’s try to explain a little better:

I want to launch a reinstallation of a running linux computer. But I can’t access the machine to press the adequate key to select pxe boot at the reboot.

So I need a way to use the current linux kernel to do a kind of reboot, using the kernel and initrd from the fog server.

I hope my explanation is a little more clear.

I want to reboot a running linux in pxe mode, to connect to a fog server.

For this task, my current track is to use kexec.

I retreive the kernel image and the init from the tftp server (the fog server in our installation) from the directory …/fog/service/ipxe

Then:

kexec -l bzImage --init=init.xz # load the new kernel
kexec -e # replace current kernel with the loaded one

And it does not work (nothing is displayed).

Has anyone tried and succeed such a reboot from linux ?

Thanks in advance for any clue