not able to write to create new files

tried:

mount -o rw,remount /


Thanks,
vikky

Could you be more specific? Where are you trying to write and create new files? When do you get the error? From the command you posted it seems you're talking about your root partition, but it's not clear what are you trying to do. In case you're trying to write/create files outside your /home/user directory, you will need root permissions (i.e. su/sudo login).

i was login as a root only

but when i try to create any file using touch command

getting error read only file system

but, when i rebooted the host its working ,but i don't know what is the exactly issue,

root fs will be automatically remounted read-only if a filesystem error is encountered that is uncorrectable. This is done to protect against any further data corruption and usually means you've got a dying drive. You probably won't see the actual error in the logs as the system wouldn't have been able to write to the log after remounting the filesystem read-only. When it occurs, you will probably see a lot of errors on the console - like ATA timeout errors, journal aborted, etc.

You should run offline fsck as soon as possible to be sure. For the root filesystem this is best done using a rescue disk (such as sysrescuecd). Your fixed HD will usually be /dev/sda if booting from sysrescuecd.

This can usually be accomplished also by passing init=/bin/bash at the boot prompt to skip system startup scripts and go straight to shell prompt. The root filesystem may or may not be mounted read-only, but with no active services running, you can run "mount -o remount,ro /" before "fsck -f /" to be sure the filesystem is actually mounted read-only. You DO NOT want to run fsck on an active (read-write) filesystem!

You'll want to check /var/log/messages for any warnings about your drive(s) that may have been written before the critical error occurred. Also install smartmon utils and run smartctl -a /dev/<your_root_fs_device> and check Reallocated_Sector_Ct and Current_Pending_Sector. Reallocated_Sector_Ct means bad sectors have been found on the disk and have been migrated to spare sectors on the disk. Current_Pending_Sector means bad sectors have been found but have not been migrated to spare sectors. Both should ideally be zero, but Current_Pending_Sector is a bigger problem than Reallocated_Sector_Ct (maybe no more spare sectors available).

If you have no pending or reallocated sectors, you probably have a bad data cable or the cables connected to the drive aren't making good contact and just need to be reseated.