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11.

&Sync

12.

<b>Sync</b>
<p>
This option requests that all file writes be committed to disk before the write request completes. This is required for complete safety of data in the face of a server crash, but incurs a performance hit.
</p>
<p>
The default is to allow the server to write the data out whenever it is ready.
</p>

13.

No w&delay

14.

<b>No wdelay</b>
<p>
This option only has effect if sync is also set. The NFS server will normally delay committing a write request to disk slightly if it suspects that another related write request may be in progress or may arrive soon. This allows multiple write requests to be committed to disk with the one operation which can improve performance. If an NFS server received mainly small unrelated requests, this behavior could actually reduce performance, so no wdelay is available to turn it off. </p>

15.

No &hide

16.

<b>No hide</b>
<p>
This option is based on the option of the same name provided in IRIX NFS. Normally, if a server exports two filesystems one of which is mounted on the other, then the client will have to mount both filesystems explicitly to get access to them. If it just mounts the parent, it will see an empty directory at the place where the other filesystem is mounted. That filesystem is "hidden".
</p>
<p>
Setting the nohide option on a filesystem causes it not to be hidden, and an appropriately authorized client will be able to move from the parent to that filesystem without noticing the change.
</p>
<p>
However, some NFS clients do not cope well with this situation as, for instance, it is then possible for two files in the one apparent filesystem to have the same inode number.
</p>
<p>
The nohide option is currently only effective on single host exports. It does not work reliably with netgroup, subnet, or wildcard exports.
</p>
<p>
This option can be very useful in some situations, but it should be used with due care, and only after confirming that the client system copes with the situation effectively.
</p>

17.

No su&btree check

18.

<b>No subtree check</b>
<p>
This option disables subtree checking, which has mild security implications, but can improve reliability is some circumstances.
</p>
<p>
If a subdirectory of a filesystem is exported, but the whole filesystem is not, then whenever a NFS request arrives, the server must check not only that the accessed file is in the appropriate filesystem (which is easy) but also that it is in the exported tree (which is harder). This check is called the subtree_check.
</p>
<p>
In order to perform this check, the server must include some information about the location of the file in the "filehandle" that is given to the client. This can cause problems with accessing files that are renamed while a client has them open (though in many simple cases it will still work).
</p>
<p>
subtree checking is also used to make sure that files inside directories to which only root has access can only be accessed if the filesystem is exported with no_root_squash (see below), even the file itself allows more general access.
</p>
<p>
As a general guide, a home directory filesystem, which is normally exported at the root and may see lots of file renames, should be exported with subtree checking disabled. A filesystem which is mostly read-only, and at least does not see many file renames (e.g. /usr or /var) and for which subdirectories may be exported, should probably be exported with subtree checks enabled.
</p>

19.

Insecure loc&ks

20.

<b>Insecure locks</b>
<p>
This option tells the NFS server not to require authentication of locking requests (i.e. requests which use the NLM protocol). Normally the NFS server will require a lock request to hold a credential for a user who has read access to the file. With this flag no access checks will be performed.
</p>
<p>
Early NFS client implementations did not send credentials with lock requests, and many current NFS clients still exist which are based on the old implementations. Use this flag if you find that you can only lock files which are world readable.
</p>