I am trying the following:
sudo dd if=/dev/sda1 of=/mnt/nfs/l bs=1M
dd: opening `/mnt/nfs/l': Permission denied
However, normal file creation and writing with "cat" works.
What could be the cause for this?
Linux, NFS v3
The most likely cause is root squashing. This is a server option that changes the the requester for file operations when coming from the clients root user. Commonly the root user is changed to nobody on the server.
If /mnt/nfs is exported from the server with root squashing then the user nobody will need to have permissions to write to the directory.