How do I manually mount a linux file system read/write as a normal user?

On an ext4 filesystem (like ext2, ext3, and most other unix-originating filesystems), the effective file permissions don't depend on who mounted the filesystem or on mount options, only on the metadata stored within the filesystem.

With Ubuntu, mounting should happen automatically when you insert the disk, or you should be able to click on an icon to mount. You can also install pmount to mount filesystems as an ordinary user from the command line.

If you have a removable filesystem that uses different user IDs from your system, you can use bindfs (in the Ubuntu package of the same name) to provide a view of any filesystem with different ownership or permissions. The removable filesystem must be mounted already, e.g. on /media/disk9; then, if you want to appear as the owner of all files, you can run

mkdir ~/disk9
sudo bindfs -u $(id -u) -g $(id -g) /media/disk9 ~/disk9

When you mount the ext4 file system, it uses the permissions that are embedded in that file system. If you wish to override these, then use the following:
1. Find the UID of the user you want to mount as: id <username> and look for UID=<userid>(<username>) GID=<groupid>(<groupname>) 2. sudo mount -o nosuid,uid=<userid>,gid=<groupid> /dev/whatever /media/wherever

This will mount the filesystem and mark the specified user as the owner of all files, and the specified group as the group for all files. nosuid is a security measure that prevents the user from bringing in suid programs and using them to gain root access to the system (i.e, a suid version of bash on the filesystem). Adding the noexec option will provide additional security, but will prevent the user from executing files on the filesystem.

Note: If you're just trying to interact with the file system yourself, you should either fix the permissions on the device, or interact with it as root if it's just a temporary thing (i.e., recovering a broken install).

If this is for mounting a USB or other removable external drive, you should check out the pmount system which can automate the process for you, or at least make it considerably easier (i.e., pmount <device> should create the folders for you, mount it as your user, and allow you to unmount it as your user)

You can use:

mount -o user /dev/devicename and user option in your fstab.