How to umount "/" file system

bkarthick · 06-03-2011, 04:53 AM

Hi,

I want to umount root partition.

below is the o/p for df -h

Filesystem Size Used Avail Use% Mounted on
/dev/sda1 12G 3.2G 7.8G 30% /
tmpfs 506M 0 506M 0% /dev/shm

If i give #umount /dev/sda1 im getting the below error.i can't unmount the file system
umount: /: device is busy
umount: /: device is busy

thanks,

Nylex · 06-03-2011, 04:55 AM

You obviously can't unmount a partition that's in use. What do you want to do to that partition? You could just get a live CD and do whatever it is on the unmounted partition.

bkarthick · 06-03-2011, 04:57 AM

I want to run fsck command.so i need to unmount the filesystem.

Nylex · 06-03-2011, 04:58 AM

You can't use a live CD for this because..?

saivnoba · 06-03-2011, 04:58 AM

karthick,
You get that error because u are executing that command from within root partition. You cannot do that. Why would you want to unmount '/' (root) partition?! If you want to edit/troubleshoot something on your linux partition, use livecd.

(When I started typing it was a zero-reply thread. By the time I hit enter, I'm the 5th. :-P )

fsck is done automatically after certain mounts during boot. But if you want to force fsck you can try (as root user),

Code:

shutdown -rF now

. This should reboot your system and when it boots it will first run fsck.

bkarthick · 06-03-2011, 05:00 AM

@saivnoba

correct me if am wrong..
How do i check my file system ?

To use fsck first i need to umount the file system right ?

bkarthick · 06-03-2011, 05:03 AM

Greetings,

And also i'm going to change the filesystem from ext2 to ext3.

for this i need to unmount the partiton.Without unmounting i can't do it.

Nylex · 06-03-2011, 05:05 AM

Again, why can't you use a live CD to do this?

NM04 · 06-03-2011, 05:13 AM

bkarthic,

first close all the running programs, and then execute umount /dev/sda1. Make sure you have a backup of data and also that you selected the correct partition.

Kind Regards.

bkarthick · 06-03-2011, 05:13 AM

Greetings,

All our servers are in Sweeden.And am in India.I can't use Live Cd or shutdown -rF now.Its all production servers.If it goes down,then i will get trashed.

Without live cd tell me how to check the filesystem.

TobiSGD · 06-03-2011, 05:17 AM

Your only option is the mentioned reboot command.
Also, if it is a production server I would recommend not to change the filesystem, unless there is a real good reason for that.

NM04 · 06-03-2011, 05:25 AM

someone please tell me what is a production server ?

TobiSGD · 06-03-2011, 05:26 AM

Quote:

Originally Posted by NM04

someone please tell me what is a production server ?

A server that is essential for a company to get their work done.

Karl Godt · 06-03-2011, 05:44 AM

On boot you could :
put in an exit into /etc/rc.d/rc.sysinit to drop out into a shell ro mount -o remount,ro / for a fsck -n /dev/sda1

boot with the kernel parameters " S init=bin/bash "

On a running system :

Create a or several ramdisks with

Code:

mkfs.ext2 /dev/ram[0-9]

and copy needed files from /bin /sbin /lib /etc into it and
use something like

Code:

mkdir /mnt/ram0
mount /dev/ram0 /mnt/ram0
mkdir /mnt/ram0/old_root
mkdir -p /mnt/ram0 /mnt/ram0/bin /mnt/ram0/sbin /mnt/ram0/lib /mnt/ram0/proc /mnt/ram0/etc
cp -a /bin /mnt/ram0
cp -a /sbin /mnt/ram0
cp -a /lib/lib*.so* /mnt/ram0/lib
cp -ar /etc /mnt/ram0
mount -o move /proc /mnt/ram0/proc
chdir /mnt/ram0
pivot_root . old_root
cd /
umount -l old_root
fsck /dev/sda1
mount /dev/sda1 old_root 
cd old_root
pivot_root . /mnt/ram0
umount -l /mnt/ram0

This would work best with a statically compiled busybox includig ash which has got fsck.ext[2-3] and of course statically compiled fsck's for /lib/lib*.so* could become too large .
For a first better understanding try dl puppylinux 5series , which comes with a /sbin/init shellscript that contains this code .

segmentation_fault · 06-03-2011, 06:31 AM

Could this work?

Code:

mount / -o remount,ro

AFAIK fsck needs the partition to be mounted read-only, not unmounted. But I don't know how the network connection is affected from this. (I have only done this localy in runlevel 1).