the file /etc/passwd has corrupted mistakenly.actually the file has saved as "oot:0:0:root:/root/sbin/bash".
first r of root has been deleted ..
can anyone tell me how can i recover as normal user
Quite simply, you cannot. You can replace the file and maybe reconstruct parts of it. If you have /etc/shadow, it should be a breeze; but an overwritten file cannot be recovered easily, especially not as a regular user. You will need to be root to read the shadow file, most probably, and to write /etc/passwd.
You may be able to boot from the CD and mount the root file system and recover it from there. What is the OS on the system?