How do you set up an Initrd for a different kernel?

haziz · 12-08-2014, 01:34 PM

I did read Patrick's initrd instructions and have done some googling but am still unclear as to the answer. How do I setup an initrd for a completely different kernel from what I am running? For eg after compiling my own kernel (let's call it vmlinuz.my-kernel.3.18)?

moisespedro · 12-08-2014, 01:56 PM

When you run:

Code:

/usr/share/mkinitrd/mkinitrd_command_generator.sh

You get something like this, right?

Code:

mkinitrd -c -k 3.17.2-smp -f ext4 -r /dev/sdb6 -m mbcache:jbd2:ext4 -u -o /boot/initrd.gz

Notice the -k switch, it refers to the directory entry under /lib/modules:

Code:

root@slack:~# ls -la /lib/modules/
total 32
drwxr-xr-x 6 root root  4096 Dez  4 19:24 ./
drwxr-xr-x 7 root root 12288 Dez  4 19:24 ../
drwxr-xr-x 3 root root  4096 Nov 19 22:58 3.10.17/
drwxr-xr-x 3 root root  4096 Nov 19 22:58 3.10.17-smp/
drwxr-xr-x 3 root root  4096 Dez  4 19:31 3.17.2-smp/
drwxr-xr-x 3 root root  4096 Dez  4 11:26 3.17.2-smp-zram/

In this case is refering to 3.17.2-smp (the kernel I am using now).

I could generate an initrd for 3.10.17, for example, by issuing:

Code:

mkinitrd -c -k 3.10.17 -f ext4 -r /dev/sdb6 -m mbcache:jbd2:ext4 -u -o /boot/initrd.gz

Don't forget to change the output (the -o switch) so you don't overwrite initrds.

haziz · 12-08-2014, 08:01 PM

Quote:

Originally Posted by moisespedro

When you run:

Code:

/usr/share/mkinitrd/mkinitrd_command_generator.sh

You get something like this, right?

Code:

mkinitrd -c -k 3.17.2-smp -f ext4 -r /dev/sdb6 -m mbcache:jbd2:ext4 -u -o /boot/initrd.gz

My custom kernel has "haziz-generic-3.18.0" appended using make menuconfig. Do I use mkinitrd -c -k haziz-generic-3.18.0 or just 3.18.0?

Code:

mkinitrd -c -k haziz-generic-3.18.0 -f ext4 -r /dev/sdb6 -m mbcache:jbd2:ext4 -u -o /boot/initrd.gz

or just

Code:

mkinitrd -c -k 3.18.0 -f ext4 -r /dev/sdb6 -m mbcache:jbd2:ext4 -u -o /boot/initrd.gz

Sorry if this seems like a very basic question.

moisespedro · 12-08-2014, 08:50 PM

Issue a:

Code:

ls -la /lib/modules

And see how the entry is listed there. It probably looks like 3.18.0-haziz-generic.

EDIT: It is usually something like: kernelversion-whatyouappended, just at look at mine, for example, "3.17.2-smp-zram", smp-zram is the custom append.

haziz · 12-09-2014, 04:42 AM

Quote:

Originally Posted by moisespedro

Issue a:

Code:

ls -la /lib/modules

And see how the entry is listed there. It probably looks like 3.18.0-haziz-generic.

EDIT: It is usually something like: kernelversion-whatyouappended, just at look at mine, for example, "3.17.2-smp-zram", smp-zram is the custom append.

Thanks I did figure it out using exactly your method. I did generate the initrd, which seems functional but the generic kernel still panics. The huge kernel (both the stock kernel and a 3.18 compile) boot (obviously without an initrd).

moisespedro · 12-09-2014, 06:27 AM

Well, maybe you open another thread? Post more details about it.

cynwulf · 12-09-2014, 10:46 AM

You need to include an initrd stanza in the bootloader configuration, just generating the initrd is not enough, did you do this?

moisespedro · 12-09-2014, 01:21 PM

In case you use LILO you could do something like this:

Code:

root@slack:~# /usr/share/mkinitrd/mkinitrd_command_generator.sh -l /boot/vmlinuz-generic-3.10.17

It will generate what you should paste into /etc/lilo.conf, like this:

Code:

# Linux bootable partition config begins
# initrd created with 'mkinitrd -c -k 3.10.17 -f ext4 -r /dev/sdb6 -m mbcache:jbd2:ext4 -u -o /boot/initrd.gz'
image = /boot/vmlinuz-generic-3.10.17
initrd = /boot/initrd.gz
root = /dev/sdb6
label = 3.10.17
read-only
# Linux bootable partition config ends

Point the -l switch to whatever is your kernel image, don't forget to edit the "initrd =" in /etc/lilo.conf to point to your initrd.
Then you run 'lilo -v'.