linux tips

If you have a dual-boot Windows and Linux machine, you may find it helpful to mount the NTFS Windows partition from time to time. The Linux kernels, however, do not come with NTFS support enabled as a rule. This is probably a good thing since the read/write issue between ext3 (Linux) and ntfs (Windows) filesystems is not evident to all users. The following example demonstrates how to mount the ntfs Windows partition in read-only mode so you won’t corrupt the filesystem. What this allows you to copy over files from the Windows-side of the machine to the Linux side. Clearly helpful examples of such copying include: MS Word documents and PowerPoint files, music, pictures, etc.

The following example is not difficult to follow. There are only a few steps, but you will have to be logged in as root (su) to perform the necessary operations.

1. You need to figure out what kernel version you are currently running. From command line, type:
#> uname -r
2. Download the NTFS RPM from the Linux-NTFS project homepage (click here). We are running CentOS 4.x on our machines, which is equivalent to RedHat Enterprise Linux 4. You should have been taken to the appropriate download page. Based on what the ‘uname -r’ command (step 1) returned, select the appropriate version to download from the first block of files (under NTFS RPMs (*.rpm)).
3. You can either choose to download the RPM and then install it using #> rpm -ivh kernel-blah_blah_blah, or just select the ‘Install’ option in the Download Manager. (It worked for me.)
4. By installing the RPM, you have just added the ntfs module to the kernel. You need to insert the module now so run:
#> /sbin/modprobe ntfs
If you get a ‘FATAL’ message, you probably downloaded/installed the wrong version. Check your current kernel version again and go back to the download page (get the right one this time, stupid).
5. As an additional check, run: #> cat /proc/filesystems and make sure that ‘ntfs’ is listed.
6. Now it’s time to mount the drive! You need to do two things first, though, before we mount anything. First of all, you need to create a directory—or mount point—for the NTFS partition. So, do something like: #> mkdir /windows/C or whatever you’d like the mountpoint to be. Secondly, you need to figure out which partition has the NTFS volume on it. A good way to look at the list of partitions on a particular harddrive is to use the ‘fdisk’ utility. For instance, if your primary harddrive (the one with Windows and Linux OS) is /dev/hda then you would run: #> fdisk -l /dev/hda. You are looking for the partition that has HPFS/NTFS under the ‘System’ category. For this example, let’s say that it is /dev/hda2.
7. Yeah, now it’s time to mount it—in read-only mode—to the mountpoint that we created in the last step:
#> mount -t ntfs -r -o umask=0222 /dev/hda2 /windows/C
8. That’s it… go check it out and make sure you can see your data.

When Ubuntu boots, grub gets loaded and will display the OS for only 5 sec, now if you want to increase this time or to decrease it.

Open up the /boot/grub/menu.lst file in your favorite text editor. you can use gedit:

sudo gedit /boot/grub/menu.lst

Now find the section that looks like this:

## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout 5

The timeout value is in seconds, specify the time you required. Save the file, and when you reboot you will have that many seconds to choose the menu item you want.

This is how my file looks

## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout         15

please note that the above text is only part of my menu.lst.

If you want grub to wait for you to take an action before continue, comment the timeout line, or erase it.

This situation presents itself infrequently, but when it does you cannot modify any files.
Here is an example of an occurrence…

A linux box wouldn’t boot properly and reported a problem with an ext2 filesystem on one of the partitions it was trying to mount.
The only option was to drop into a ‘repair shell’ to run e2fsck/fsck on the various partitions to see which one was having trouble.
As it so happens there were other problems that prompted this to happen: the only listings in /etc/fstab were for the cdrom and floppy drives.
Nothing else was being mounted, with the exception of the root partition / .It was impossible to mount filesystems or edit files (like /etc/fstab) in the read-only environment, but there is a way around it…

#> mount -o remount,rw /dev/hdb# / , where hdb# is the logical mount point of the root (/) partition. For instance, if your root partition (/) is actually /dev/hdb1 then hdb# is hdb1.

This mounts the root partition / as a read-write filesystem and by doing so you should be able to edit files and mount other filesystems…ugh!

Here is a quick tip that will show how you can tell your Linux system to perform a fsck on its partitions on the next reboot. Normally this will happen by default, after some time as configured in the filesystem at creation time (or changed later): after a number of days or a number of filesystem mounts. If you are using ext3 filesystems you can check these intervals configured with:
tune2fs -l
…
Mount count: 5
Maximum mount count: 37
…
Last checked: Sat May 17 16:39:18 2008
Check interval: 15552000 (6 months)
Next check after: Thu Nov 13 15:39:18 2008

If for some reason, you want to force the system to run fsck on the next reboot just create an empty file called forcefsck in your system / like this:
touch /forcefsck
During the first reboot the system will run fsck and after completing this it will also remove the /forcefsck file from the system.

The following example shows the structure of a GRUB menu file. The example installation has a Linux boot partition under /dev/sda5, a root partition under /dev/sda7, and a Windows installation under /dev/sda1.

gfxmenu (hd0,4)/boot/message
color white/blue black/light-gray
default 0
timeout 8

title linux
root (hd0,4)
kernel /boot/vmlinuz root=/dev/sda7 vga=791 resume=/dev/sda9
initrd /boot/initrd

title windows
rootnoverify (hd0,4)
chainloader(hd0,0)+1

The first block defines the configuration of the splash screen:

gfxmenu (hd0,4)/message
The background image message is located in the top directory of the /dev/sda5 partition.
color white/blue black/light-gray
Color scheme: white (foreground), blue (background), black (selection), and light gray (background of the selection). The color scheme has no effect on the splash screen, only on the customizable GRUB menu that you can access by exiting the splash screen with Esc.
default 0
The first menu entry title linux is the one to boot by default.
timeout 8
After eight seconds without any user input, GRUB automatically boots the default entry. To deactivate automatic boot, delete the timeout line. If you set timeout 0, GRUB boots the default entry immediately.

The second and largest block lists the various bootable operating systems. The sections for the individual operating systems are introduced by title.

* The first entry (title linux) is responsible for booting Linux. The kernel (vmlinuz) is located in the first logical partition (the boot partition) of the first hard disk. Kernel parameters, such as the root partition and VGA mode, are appended here. The root partition is specified according to the Linux naming convention (/dev/sda7/), because this information is read by the kernel and has nothing to do with GRUB. The initrd is also located in the first logical partition of the first harddisk.
* The second entry is responsible for loading Windows. Windows is booted from the first partition of the first hard disk (hd0,0). The command chainloader +1 causes GRUB to read and execute the first sector of the specified partition.

The menu file can be changed whenever necessary. GRUB then uses the modified settings during the next boot.

I reinstalled my vista, i found that my ubuntu grub was lost..

These are the steps i took to get back my ubuntu grub..

1. Boot the Desktop/Live CD.

2. Open a terminal (Applications -> Accessories -> Terminal)

3. Start grub as root with the following command :

$ sudo grub

I got the output as

[ Minimal BASH-like line editing is supported. For

grub>

5. Now type these :

grub> find /boot/grub/stage1

i got it as (hda0,10)

6. Use the information from the above to set the root device:

grub> root (hd0,10)

7. Now install the grub:

grub> setup (hd0)</strong>