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I am trying the following:

sudo dd if=/dev/sda1 of=/mnt/nfs/l bs=1M

It fails:

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

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Did you use 'sudo' when testing normal file creation and writing with cat? – sciurus Jul 20 '11 at 20:58
up vote 5 down vote accepted

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.

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