LinuxQuestions.org - How to umount "/" file system

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How to umount "/" file system

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,

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.

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

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

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.

@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 ?

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.

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

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.

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.

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.

someone please tell me what is a production server ?

Quote:

Originally Posted by NM04 (Post 4374961)

someone please tell me what is a production server ?

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

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 .

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).

Quote:

Originally Posted by segmentation_fault (Post 4375017)

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).

I doubt that this will work in normal use, you will have to do that in runlevel 1. But as the OP states that he can't reboot the machine because it is a production machine I doubt that switching to runlevel 1 is an option.

Greetings,

I WIll try and get back to you..

Thanks

You don't fiddle with production servers. The risks are far too high if this is mission critical.

Do the changes on your backup server first and test; next make that one the primary server and you can now do the exercise on the old primary.