Linux Blog

How To Make ISO image from CD

Use following command to create ISO image of CD
Note: /dev/hdc is my cdrom device
1. dd if=/dev/hdc of=/home/nikesh/example.iso bs=2048 conv=notrunc
— OR –

2. cat /dev/hdc > /home/nikesh/example.iso
Both commands do exactly the same, but the first one might be easier to remember.

How to recover damaged Superblock

If a filesystem check fails and returns the error message “Damaged Superblock”

Solution:
There are backups of the superblock located on several positions and we can restore them with a simple command. Backup locations are: 8193, 32768, 98304, 163840, 229376 and 294912. ( 8193 in many cases only on older systems, 32768 is the most current position for the first backup )

Now, suppose you get a ¨Damaged Superblock¨ error message at filesystem check ( after a power failure ) and you get a root-prompt in a recovery console, then you give the command:

# e2fsck -b 32768 /dev/hda5

System will then check the filesystem with the information stored in that backup superblock and if the check was successful it will restore the backup to position 0.

If this is not working try using the other copy of Superblock located at the above mention location in your HD.

How to crash Linux?

As root, you can do whatever you want.

Try this command, as root (reconsider if you really want to crash):

# cp /dev/zero /dev/men

As root, you can even erase all the files on your system with a similarly innocuously looking one-liner (don’t do it):

# rm -rf /

This is not to say that Linux is easy to crash, but that the system administrator (”root”) has the complete power over the system so think before when working on Linux as “root” user.

Create Linux Filesystem From An Ordinary File

Under Linux, you can create a regular file, format it as an ext2, ext3, or reiser file system, and then mount it just like a physical drive. It's then possible to read and write files to this newly-mounted device. You can also copy the complete file system, since it is just a file, to another computer.

First, you want to create a 20MB file or any size you want by executing the following command:

     $ dd if=/dev/zero of=disk-image count=40960
     40960+0 records in
     40960+0 records out

Next, to format this as an ext3 filesystem, you just execute the following command:

     $ /sbin/mkfs -t ext3 -q disk-image
     mke2fs 1.32 (09-Nov-2002)
     disk-image is not a block special device.
     Proceed anyway? (y,n) y

You are asked whether to proceed because this is a file, and not a block device. That is OK.

Next, you need to create a directory that will serve as a mount point for the loopback device.

      $ mkdir fs

You must do the next command as root, or with an account that has superuser privileges.

      # mount -o loop=/dev/loop0 disk-image fs

You can now create new files, write to them, read them, and do everything you normally would do on a disk drive. To make normal user to use this filesystem you need to give valid permission to the directory holding this filesystem.

Allow normal user to mount cdrom

By default, this device is not accessible by all of your users. To allow users to mount the CDROM drive, login as root and execute the following command

# chmod a+r /dev/cdrom

This will allow any user on your Linux system to mount the CDROM drive from their console or desktop.