The file
.I /etc/exports
serves as the access control list for file systems which may be
-exported to NFS clients. It it used by
+exported to NFS clients. It is used by
.IR exportfs (8)
to give information to
.IR mountd (8)
.PP
The file format is similar to the SunOS
.I exports
-file, except that several additional options are permitted. Each line
-contains an export point and a list of machine or netgroup names allowed
-to mount the file system at that point. An optional parenthesized list
-of export parameters may follow each machine name. Blank lines are
-ignored, and a # introduces a comment to the end of the line. Entries may
-be continued across newlines using a backslash.
+file. Each line contains an export point and a whitespace-separated list
+of clients allowed to mount the file system at that point. Each listed
+client may be immediately followed by a parenthesized, comma-separated
+list of export options for that client. No whitespace is permitted
+between a client and its option list.
+.PP
+Blank lines are ignored. A pound sign ("#") introduces a comment to the
+end of the line. Entries may be continued across newlines using a
+backslash. If an export name contains spaces it should be quoted using
+double quotes. You can also specify spaces or other unusual character in
+the export name using a backslash followed by the character code as three
+octal digits.
.PP
.SS Machine Name Formats
NFS clients may be specified in a number of ways:
.IP "wildcards
Machine names may contain the wildcard characters \fI*\fR and \fI?\fR.
This can be used to make the \fIexports\fR file more compact; for instance,
-\fI*.cs.foo.edu\fR matches all hosts in the domain \fIcs.foo.edu\fR. However,
-these wildcard characters do not match the dots in a domain name, so the
-above pattern does not include hosts such as \fIa.b.cs.foo.edu\fR.
+\fI*.cs.foo.edu\fR matches all hosts in the domain
+\fIcs.foo.edu\fR. As these characters also match the dots in a domain
+name, the given pattern will also match all hosts within any subdomain
+of \fIcs.foo.edu\fR.
.IP "IP networks
You can also export directories to all hosts on an IP (sub-) network
simultaneously. This is done by specifying an IP address and netmask pair
as
-.IR address/netmask .
-.TP
+.IR address/netmask
+where the netmask can be specified in dotted-decimal format, or as a
+contiguous mask length (for example, either `/255.255.252.0' or `/22' appended
+to the network base address result in identical subnetworks with 10 bits of
+host). Wildcard characters generally do not work on IP addresses, though they
+may work by accident when reverse DNS lookups fail.
+'''.TP
'''.B =public
'''This is a special ``hostname'' that identifies the given directory name
'''as the public root directory (see the section on WebNFS in
the
.IR ro " option.
.TP
-.IR sync
-This option requests that all file writes be committed to disc 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.
-The default is to allow the server to write the data out whenever it
-is ready. This can be explicitly requested with the
-.IR async " option.
+.IR async
+This option allows the NFS server to violate the NFS protocol and
+reply to requests before any changes made by that request have been
+committed to stable storage (e.g. disc drive).
+
+Using this option usually improves performance, but at the cost that
+an unclean server restart (i.e. a crash) can cause data to be lost or
+corrupted.
+
+In releases of nfs-utils upto and including 1.0.0, this option was the
+default. In this and future releases,
+.I sync
+is the default, and
+.I async
+must be explicit requested if needed.
+To help make system adminstrators aware of this change, 'exportfs'
+will issue a warning if neither
+.I sync
+nor
+.I async
+is specified.
.TP
.IR no_wdelay
-This option only has effect if
-.I sync
+This option has no effect if
+.I async
is also set. The NFS server will normally delay committing a write request
to disc slightly if it suspects that another related write request may be in
progress or may arrive soon. This allows multiple write requests to
instance, it is then possible for two files in the one apparent
filesystem to have the same inode number.
+The
+.I nohide
+option is currently only effective on
+.I "single host
+exports. It does not work reliably with netgroup, subnet, or wildcard
+exports.
+
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.
The default of having subtree checks enabled, can be explicitly
requested with
.IR subtree_check .
+
+.TP
+.IR insecure_locks
+.TP
+.IR no_auth_nlm
+This option (the two names are synonymous) 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.
+
+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.
+
+The default behaviour of requiring authentication for NLM requests can
+be explicitly requested with either of the synonymous
+.IR auth_nlm ,
+or
+.IR secure_locks .
+
'''.TP
'''.I noaccess
'''This makes everything below the directory inaccessible for the named
'''.TP
'''.IR link_absolute
'''Leave all symbolic link as they are. This is the default operation.
+
+.TP
+.IR mountpoint= path
+.TP
+.I mp
+This option makes it possible to only export a directory if it has
+successfully been mounted.
+If no path is given (e.g.
+.IR mountpoint " or " mp )
+then the export point must also be a mount point. If it isn't then
+the export point is not exported. This allows you to be sure that the
+directory underneath a mountpoint will never be exported by accident
+if, for example, the filesystem failed to mount due to a disc error.
+
+If a path is given (e.g.
+.IR mountpoint= "/path or " mp= /path)
+then the nominted path must be a mountpoint for the exportpoint to be
+exported.
+
.SS User ID Mapping
.PP
.I nfsd
'''# Mapping for client foobar:
'''# remote local
'''uid 0-99 - # squash these
-'''uid 100-500 1000 # map 100-500 to 1000-1500
+'''uid 100-500 1000 # map 100-500 to 1000-1400
'''gid 0-49 - # squash these
'''gid 50-100 700 # map 50-100 to 700-750
'''.fi
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