Document fsid=

[nfs-utils.git] / utils / exportfs / exports.man

diff --git a/utils/exportfs/exports.man b/utils/exportfs/exports.man
index 4b31ccf9c03e1316f3483a8d7cf3810a29ee7f91..034a896225e09c84001e9365b941397b54350306 100644 (file)
--- a/utils/exportfs/exports.man
+++ b/utils/exportfs/exports.man
@@ -17,15 +17,18 @@ and to the kernel based NFS file server daemon
 .PP
 The file format is similar to the SunOS
 .I exports
 .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. If export name contains spaces
-it should be quoted using double-quotes. You can also specify spaces
-or any other unusual characters in the export path name using a
-backslash followed by the character code as 3 octal digits.
+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:
 .PP
 .SS Machine Name Formats
 NFS clients may be specified in a number of ways:


@@ -42,9 +45,10 @@ parts or those containing a single dash (\-) are ignored.
 .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,
 .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
 .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


@@ -53,8 +57,9 @@ as
 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
 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).
-.TP
+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
 '''.B =public
 '''This is a special ``hostname'' that identifies the given directory name
 '''as the public root directory (see the section on WebNFS in


@@ -91,17 +96,31 @@ This can also be made explicit by using
 the
 .IR ro " option.
 .TP
 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
 .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
 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


@@ -218,6 +237,47 @@ or
 '''.TP
 '''.IR link_absolute
 '''Leave all symbolic link as they are. This is the default operation.
 '''.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.
+
+.TP
+.IR fsid= num
+This option forces the filesystem identification portion of the file
+handle and file attributes used on the wire to be
+.I num
+instead of a number derived from the major and minor number of the
+block device on which the filesystem is mounted.  Any 32 bit number
+can be used, but it must be unique amongst all the exported filesystems.
+
+This can be useful for NFS failover, to ensure that both servers of
+the failover pair use the same NFS file handles for the shared filesystem
+thus avoiding stale file handles after failover.
+
+Some Linux filesystems are not mounted on a block device; exporting
+these via NFS requires the use of the
+.I fsid
+option (although that may still not be enough).
+
+The value  0 has a special meaning when use with NFSv4.  NFSv4 has a
+concept of a root of the overall exported filesystem. The export point
+exported with fsid=0 will be used as this root.
+

 .SS User ID Mapping
 .PP
 .I nfsd
 .SS User ID Mapping
 .PP
 .I nfsd