Backup files from corrupt disk to usb drive in single user mode I try to backup my files of a corrupt system. I can start into the single user mode and want so store my home folder to my backup system. To mount my usb drive I need to mount the root disk as writeable. Therefor I used the command 

/sbin/mount -uw /


The command will be executed withoud any response, after that I tried to create a folder 

mkdir /backup


But this returns 

mkdir:backup: File exists


But there is no folder or file which has been created??? What am I doing wrong?
Thanks
Single user mode is the wrong tool for this job.   Connect an external drive if you want to use one and then restart in to Recovery HD ( or Internet recovery).

Use the terminal application from there to make your copies and backups. It's handles mounting all the filesystems properly so you can move things around.