NAME

exports − defines NFS file systems to be exported

SYNTAX

/etc/exports

DESCRIPTION

The /etc/exports file describes the local file systems and directories that can be mounted by remote hosts through the use of the NFS protocol. The exports file can also be used to restrict access to a particular set of remote systems. The mount request daemon mountd() accesses the exports file each time it receives a mount request from an NFS client.

Each entry in the /etc/exports file consists of a file system or directory name followed by an optional list of options and/or an optional list of identifiers. The identifiers define which remote hosts can mount that particular file system or directory. The identifiers listed beside the name of each file system or directory can be either host names or YP netgroups names.  When the mountd daemon receives a mount request from a client, it searches for a match in the list of identifiers, first by checking the client host name with the host name identifiers and second by checking the client host name in a YP netgroups. When it finds a match, mountd makes that file system or directory available to the requesting client.

The exports file format is defined as left-justified file system names, followed by any amount of white space, followed by the list of identifiers, each separated by a space. A blank identifier list beside a file system or directory name tells the mount daemon mountd to export that particular file system or directory to anyone requesting it. A number sign, #, anywhere on a line specifies the beginning of a comment extending to the end of the line. White space in the left-most position of a line specifies a continuation line.

Each file system must be explicitly defined.  Exporting only the root, /, will not allow clients to mount /usr. Exporting only /usr will not allow clients to mount /usr/local, if it is a file system. The options can only be used on file system entries. When an option is used, the meaning of that option is set for the complete file system.  The options operate on a per file system basis, not per user.  In addition, you can export individual directories within a file system.  No duplicate directory entries are allowed.  The first entry is valid and following duplicates are ignored.

OPTIONS

−nSpecial security flag does not give out the fhandle of the root of the file system. 

−oExport the file system read only.  Users on the client system cannot write to the file system. 

−r=uid
Map client superuser access to uid on the file system.  If you want to allow client superuser access to the file system with the same permissions as a local superuser, use −r=0.  Use the −r=0 option only if you trust the superuser on the client system.  The default is −r=-2 which maps superuser to nobody.  This limits the access to world readable files. 

EXAMPLE

/usr alpha beta gamma   # export /usr to these hosts
/usr/staff/doe  beta    # export this directory to beta, only
/usr clients            # export to hosts in netgroup clients
/usr/man −o clients     # export file system to netgroup clients,
                          read only
/usr/local −r=0 −n      # export file system to world, client maps to
                          root, need to restrict access to fhandle of
                          root of /usr/local file system with −n
/usr2 erie suez grand   # export /usr2 to these hosts

FILES

/etc/exports

SEE ALSO

hosts(5), mountd(8nfs), netgroup(5yp)
Guide to Networking

File Formats