This is the FAQ section. Most of it was written by Alan Cox.
This is caused by a bug in some oldish nfsd versions. It is fixed in nfs-server2.2beta16 and later.
can't register with portmap: system error on send
You are probably using a Caldera system. There is a bug in the rc scripts. Please contact Caldera to obtain a fix.
The reason is that nfsd caches open file handles for performance reasons (remember, it runs in user space). While nfsd has a file open (as is the case after writing to it), the kernel won't allow you to execute it. Nfsds newer than  spring 95 release open files after a few seconds, older ones would cling to them for days.
The Linux NFS server defaults to read only. RTFM the ``exports''
and nfsd manual pages. You will need to alter
On older versions of Linux you must mount a NFS servers with
Basically don't do it then.
No, not at present.
Make sure your users are in 8 groups or less. Older servers require this.
Do not unmount NFS servers when rebooting or halting, just
ignore them, it will not hurt anything if you don't unmount them.
The command is
umount -avt nonfs.
NFS writes are normally synchronous (you can disable this if you don't mind risking losing data). Worse still BSD derived kernels tend to be unable to work in small blocks. Thus when you write 4K of data from a Linux box in the 1K packets it uses BSD does this
read 4K page alter 1K write 4K back to physical disk read 4K page alter 1K write 4K page back to physical disk etc..