1FEDFS-MAP-NFS4(8) System Manager's Manual FEDFS-MAP-NFS4(8)
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7 fedfs-map-nfs4 - generate automounter program map entries for FedFS
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10 fedfs-map-nfs4 domainname
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13 RFC 5716 introduces the Federated File System (FedFS, for short).
14 FedFS is an extensible standardized mechanism by which system adminis‐
15 trators construct a coherent namespace across multiple file servers
16 using file system referrals. For further details, see fedfs(7).
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19 The fedfs-map-nfs4(8) command provides a FedFS program map for the
20 local system's automounter. Although it is typically intended to be
21 invoked by the automounter, it is also safe to invoke directly for
22 scripting or debugging purposes. See autofs(5) for information about
23 how program maps work.
24 Operation
26 The fedfs-map-nfs4(8) command locates FedFS domains by looking for DNS
27 SRV records that advertise file servers exporting FedFS domain root
28 replicas. The domainname argument determines what FedFS domain is to
29 be mounted.
30 It retrieves and sorts the domain root replica records according to SRV
32 record sorting rules outlined in RFC 2782. It then generates a sun
33 format map entry on stdout representing the set of servers contained in
34 the SRV record, a standard export path to the domain root, and appro‐
35 priate NFS mount options. Error messages are output on stderr.
36 Globally useful names
38 Across all FedFS-enabled file system clients, a unique file object in a
39 FedFS domain is always accessed via the same pathname. Such pathnames
40 are referred to as globally useful names. See fedfs(7) for a full dis‐
41 cussion.
42 The top-level directory of a globally useful name is always the net‐
44 worked file system type (NFS version 4, CIFS, and so on). A fedfs-map-
45 nfs4(8) program map entry is used with the NFS version 4 top-level
46 directory to provide globally useful names via the NFS version 4 proto‐
47 col.
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50 Typically, a fedfs-map-nfs4(8) entry in /etc/auto.master looks like
51 this:
52 /nfs4 /usr/sbin/fedfs-map-nfs4
54 Under the /nfs4 directory on the local system, the automounter uses
56 fedfs-map-nfs4(8) to convert a FedFS domain name to a set of servers
57 and an export path, which are then passed to mount.nfs(8). The auto‐
58 mounter mounts this FedFS domain on the directory /nfs4/domainname.
59 After configuring and restarting autofs, to access files in the exam‐
61 ple.net FedFS domain, for instance, you can start with:
62 $ cd /nfs4/example.net
64 The automounter uses the fedfs-map-nfs4(8) command to look up the file
66 servers that provide the domain root for the example.net domain. It
67 then mounts one of these servers on /nfs4/example.net.
68 If the fedfs-map-nfs4(8) command cannot find the requested domain, no
70 local directory is created and no mount operation is performed. Appli‐
71 cations receive an ENOENT error in this case.
72 While these mounted domains remain active on the local system, the
74 mounted-on directories remain visible. After a period of inactivity,
75 the automounter automatically unmounts a FedFS domain.
76 Local applications browsing the top-level directory do not see all
78 available FedFS domains. They see only the ones that are mounted and
79 active.
80 Mount option inheritance
82 The Linux NFS client treats an NFS referral as a server-initiated mount
83 request. The referring fileserver provides only a list of server names
84 and export paths. The mount options for this new mount are inherited
85 from the new mount point's parent directory on the client.
86 As applications proceed deeper into a domain's namespace, they can
88 encounter both file sets to which they have read-only access, and file
89 sets to which they have read-write access. To allow applications
90 proper access to both types of file sets, typically file-access clients
91 mount domain root directories in read-write mode. All submounts of the
92 domain root are then mounted read-write as well. Write access is con‐
93 trolled by fileservers.
94 For example, a domain root may contain an NFS version 4 referral to an
96 export containing user home directories. The domain root may be
97 exported read-only so file-access clients cannot update it, but user
98 home directories would not be very useful if they could not be written
99 to by their owners. The fileserver continues to employ user creden‐
100 tials to limit access as appropriate.
101 Network file system clients follow file system referrals as applica‐
103 tions encounter them, which is similar to how an automounter works.
104 Consider the initial mount of the domain root as if you are mounting a
105 single whole file system, even though underneath, additional NFS mounts
106 come and go as needed.
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109 /etc/auto.master master automounter map
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112 fedfs(7), nfs(5), autofs(5),
113 RFC 2782 for a discussion of DNS SRV records
115 RFC 5716 for FedFS requirements and overview
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119 This page is part of the fedfs-utils package. A description of the
120 project and information about reporting bugs can be found at
121 http://wiki.linux-nfs.org/wiki/index.php/FedFsUtilsProject.
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124 Chuck Lever <chuck.lever@oracle.com>
125 3 February 2014 FEDFS-MAP-NFS4(8)