On 4/22/05, Logu <[EMAIL PROTECTED]> wrote:
> Hi,
> 
> I have gone through the pivot_root man pages and some internet pages. But I
> could not clearly understand the command (or system call) syntax which says
> "pivot_root new_root put_old".
> 
> 

Read the initrd.txt file in the kernel/Documentation.

It is the way most of the systems like redhat boot with the initrd
file. The initrd file is a small ram based file system which is used
for loading some basic modules. Mostly the ext3fs modules in redhat.
You can try gunzip ing and mounting the initrd file using a loop back
device.
On my FC3
[EMAIL PROTECTED] boot]# cp initrd-2.6.9-1.667.img /root/initrd.gz
[EMAIL PROTECTED] boot]# cd
[EMAIL PROTECTED] ~]# gunzip initrd.gz
OMG, its not working. I am not sure wats new with initrd. Did
redhat/fedora do something with the initrd file?

I tried the usual stuff i do with redhat 7.3 or redhat 9.0...
[EMAIL PROTECTED] ~]# cp /boot/initrd-2.4.20-8.img initrd.gz
[EMAIL PROTECTED] ~]# gunzip initrd.gz
[EMAIL PROTECTED] ~]# mount -o loop initrd /temp2


[EMAIL PROTECTED] ~]#  cat /temp2/linuxrc
#!/bin/nash
echo "Loading jbd.o module"
insmod /lib/jbd.o
echo "Loading ext3.o module"
insmod /lib/ext3.o
echo Mounting /proc filesystem
mount -t proc /proc /proc
echo Creating block devices
mkdevices /dev
echo Creating root device
mkrootdev /dev/root
echo 0x0100 > /proc/sys/kernel/real-root-dev
echo Mounting root filesystem
mount -o defaults --ro -t ext3 /dev/root /sysroot
pivot_root /sysroot /sysroot/initrd
umount /initrd/proc

There you can see pivot_root being called. Redhat maintains a
directory /initrd which is used as an old root. Try deleting this
directory and you system will not boot!!

old root is the small filesystem (initrd) that was used to load the
modules and has some very basic set of utilities.
new root is the actual root file system that needs to be booted.


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