how to decide the parameter value of root in grub.conf

redhatz_zhao · 07-21-2010, 01:11 AM

After I installed Linux OS(for example:SuSE10,redhat5),the [root] parmeter of [kernel] in created grub.conf seems that sometimes it's defined to device name.sometimes it's defined to Label or sometimes UUID.

So ,I want to know what is that relative to? Hard disk type or OS version or both?

Thanks.

sem007 · 07-21-2010, 11:00 AM

Hi redhatz_zhao,

Quote:

After I installed Linux OS(for example:SuSE10,redhat5),the [root] parmeter of [kernel] in created grub.conf seems that sometimes it's defined to device name.sometimes it's defined to Label or sometimes UUID.

So ,I want to know what is that relative to? Hard disk type or OS version or both?

Thanks.

root argument tells the kernel what device to be used as a root file system.

you can define value as a partition, LABEL or UUID. This value is related root file system.

mostly in redhat system it configured as partition or LABEL
in ubuntu 10.04 it configured as UUID number
in debian lenny it configured as partition

you can use different parameter for root file system. for example if your file system on /dev/sda1 and label is "/"
you can use

Code:

kernel /vmlinuz-2.4.18-0.12-jul2001 ro root=/dev/sda1 ro quite
OR
kernel /vmlinuz-2.4.18-0.12-jul2001 ro root=LABEL=/ ro quite
OR
kernel /vmlinuz-2.4.18-0.12-jul2001 ro root=UUID=uuid number ro quite

whatever option you use it will always point root file system. if your parameter is incorrect then linux wan't boot.

HTH

PTrenholme · 07-21-2010, 01:04 PM

Note, however, that using a drive/partition specification requires that you change your GRUB boot configuration file if you change your partitioning, and that using a partition label requires that your boot drive label(s) be unique for your whole drive farm.

redhatz_zhao · 07-22-2010, 01:37 AM

Hi Sem007

thanks for your detailed explanation.
Now, what I want to know is what root argument is when installed OS.
on other words,what is initial kernel's options?
the following is rule or experience?Is there offical document that specifes these rules?

thanks.
-----------------------------
mostly in redhat system it configured as partition or LABEL
in ubuntu 10.04 it configured as UUID number
in debian lenny it configured as partition
-----------------------------

Quote:

Originally Posted by sem007

Hi redhatz_zhao,

root argument tells the kernel what device to be used as a root file system.

you can define value as a partition, LABEL or UUID. This value is related root file system.

mostly in redhat system it configured as partition or LABEL
in ubuntu 10.04 it configured as UUID number
in debian lenny it configured as partition

you can use different parameter for root file system. for example if your file system on /dev/sda1 and label is "/"
you can use

Code:

kernel /vmlinuz-2.4.18-0.12-jul2001 ro root=/dev/sda1 ro quite
OR
kernel /vmlinuz-2.4.18-0.12-jul2001 ro root=LABEL=/ ro quite
OR
kernel /vmlinuz-2.4.18-0.12-jul2001 ro root=UUID=uuid number ro quite

whatever option you use it will always point root file system. if your parameter is incorrect then linux wan't boot.

HTH

redhatz_zhao · 07-22-2010, 01:40 AM

Quote:

Originally Posted by PTrenholme

Note, however, that using a drive/partition specification requires that you change your GRUB boot configuration file if you change your partitioning, and that using a partition label requires that your boot drive label(s) be unique for your whole drive farm.

Hi,PTrenholme

thanks for your notation.

redhatz_zhao · 07-22-2010, 01:55 AM

[supplementation]

Today,I tried to install SUSE 10.I fount that it seems root argument is decide by editing fstab when creating / partition.
Is the guess right?

but not all the OS's fstab can be customized in installing

sem007 · 07-22-2010, 02:53 AM

Hi

Quote:

thanks for your detailed explanation.
Now, what I want to know is what root argument is when installed OS.
on other words,what is initial kernel's options?
the following is rule or experience?Is there offical document that specifes these rules?

thanks.
-----------------------------
mostly in redhat system it configured as partition or LABEL
in ubuntu 10.04 it configured as UUID number
in debian lenny it configured as partition
-----------------------------

It is based on my experience.You can search their sites for the same.

Quote:

[supplementation]

Today,I tried to install SUSE 10.I fount that it seems root argument is decide by editing fstab when creating / partition.
Is the guess right?

but not all the OS's fstab can be customized in installing

Yes you are right. You can change fstab option (in expert mode)during suse 10 installation.In redhat,ubuntu there is no such option available.

HTH

babunix · 07-26-2010, 10:42 AM

Hello All,

I am new member to this forum.I am searching about grub problem and i found this useful information.

one question about UUID.

How can i find UUID?

Thanks,

sem007 · 07-26-2010, 10:46 AM

Hello Babu Wel-come to LQ,

Use blkid command to find UUID
for exa.

Code:

blkid /dev/sda1

babunix · 07-26-2010, 11:06 AM

thanks sem007

djsmiley2k · 07-26-2010, 11:14 AM

Quote:

Originally Posted by sem007

Code:

kernel /vmlinuz-2.4.18-0.12-jul2001 ro root=/dev/sda1 ro quite
OR
kernel /vmlinuz-2.4.18-0.12-jul2001 ro root=LABEL=/ ro quite
OR
kernel /vmlinuz-2.4.18-0.12-jul2001 ro root=UUID=uuid number ro quite

Not being nit picky but in case anyone who doesn't realise sees this and ends up copying it word for word: It should be `quiet` not `quite`

PTrenholme · 07-26-2010, 12:05 PM

Quote:

Originally Posted by babunix

Hello All,

I am new member to this forum.I am searching about grub problem and i found this useful information.

one question about UUID.

How can i find UUID?

Thanks,

If your distribution uses udev (most distributions do so), lots of useful information can be found in the subdirectories of /dev/disk. For example, a ls -l /dev/disk/by-uuid will usually show you the UUIDs of all the disk devices attached you your system.