1 ==========
2 NFS Client
3 ==========
4
5 The NFS client
6 ==============
7
8 The NFS version 2 protocol was first documente
9 Since then two more major releases of NFS have
10 being documented in RFC1813 (June 1995), and N
11 2003).
12
13 The Linux NFS client currently supports all th
14 and work is in progress on adding support for
15 protocol.
16
17 The purpose of this document is to provide inf
18 special features of the NFS client that can be
19 administrators.
20
21
22 The nfs4_unique_id parameter
23 ============================
24
25 NFSv4 requires clients to identify themselves
26 string. File open and lock state shared betwe
27 is associated with this identity. To support
28 and transparent state migration, this identity
29 across client reboots.
30
31 Without any other intervention, the Linux clie
32 the local system's node name. System administ
33 take care to ensure that node names are fully
34 over the lifetime of a client system. Node na
35 administrative requirements that require parti
36 work well as part of an nfs_client_id4 string.
37
38 The nfs.nfs4_unique_id boot parameter specifie
39 used together with a system's node name when
40 a server. Thus, if the system's node name is
41 nfs.nfs4_unique_id can help prevent collisions
42
43 The nfs.nfs4_unique_id string is typically a U
44 anything that is believed to be unique across
45 nfs4_unique_id string should be chosen when a
46 just as a system's root file system gets a fre
47 install time.
48
49 The string should remain fixed for the lifetim
50 changed safely if care is taken that the clien
51 outstanding NFSv4 state has expired, to preven
52
53 This string can be stored in an NFS client's g
54 via a net boot facility such as PXE. It may a
55 module parameter.
56
57 This uniquifier string will be the same for al
58 containers unless it is overridden by a value
59 /sys/fs/nfs/net/nfs_client/identifier which wi
60 namespace of the process which writes.
61
62
63 The DNS resolver
64 ================
65
66 NFSv4 allows for one server to refer the NFS c
67 migrated onto another server by means of the s
68 attribute. See `RFC3530 Section 6: Filesystem
69 `Implementation Guide for Referrals in NFSv4`_
70
71 .. _RFC3530 Section 6\: Filesystem Migration a
72 .. _Implementation Guide for Referrals in NFSv
73
74 The fs_locations information can take the form
75 a path, or a DNS hostname and a path. The latt
76 do a DNS lookup in order to mount the new volu
77 upcall to allow userland to provide this servi
78
79 Assuming that the user has the 'rpc_pipefs' fi
80 /var/lib/nfs/rpc_pipefs, the upcall consists o
81
82 (1) The process checks the dns_resolve cach
83 valid entry. If so, it returns that ent
84
85 (2) If no valid entry exists, the helper sc
86 (may be changed using the 'nfs.cache_ge
87 is run, with two arguments:
88 - the cache name, "dns_resolve"
89 - the hostname to resolve
90
91 (3) After looking up the corresponding ip a
92 writes the result into the rpc_pipefs p
93 '/var/lib/nfs/rpc_pipefs/cache/dns_reso
94 in the following (text) format:
95
96 "<ip address> <hostname> <ttl>
97
98 Where <ip address> is in the usual IPv4
99 (ffee:ddcc:bbaa:9988:7766:5544:3322:110
100 <hostname> is identical to the second a
101 script, and <ttl> is the 'time to live'
102 units of seconds).
103
104 .. note::
105 If <ip address> is invalid, say th
106 entry is created, which will cause
107 as having no valid DNS translation
108
109
110
111
112 A basic sample /sbin/nfs_cache_getent
113 =====================================
114 .. code-block:: sh
115
116 #!/bin/bash
117 #
118 ttl=600
119 #
120 cut=/usr/bin/cut
121 getent=/usr/bin/getent
122 rpc_pipefs=/var/lib/nfs/rpc_pipefs
123 #
124 die()
125 {
126 echo "Usage: $0 cache_name entry_name"
127 exit 1
128 }
129
130 [ $# -lt 2 ] && die
131 cachename="$1"
132 cache_path=${rpc_pipefs}/cache/${cachename
133
134 case "${cachename}" in
135 dns_resolve)
136 name="$2"
137 result="$(${getent} hosts ${name}
138 [ -z "${result}" ] && result="0"
139 ;;
140 *)
141 die
142 ;;
143 esac
144 echo "${result} ${name} ${ttl}" >${cache_p
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