1nfsd(7) Miscellaneous Information Manual nfsd(7)
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6 nfsd - special filesystem for controlling Linux NFS server
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9 mount -t nfsd nfsd /proc/fs/nfsd
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12 The nfsd filesystem is a special filesystem which provides access to
13 the Linux NFS server. The filesystem consists of a single directory
14 which contains a number of files. These files are actually gateways
15 into the NFS server. Writing to them can affect the server. Reading
16 from them can provide information about the server.
17 This file system is only available in Linux 2.6 and later series ker‐
19 nels (and in the later parts of the 2.5 development series leading up
20 to 2.6). This man page does not apply to 2.4 and earlier.
21 As well as this filesystem, there are a collection of files in the
23 procfs filesystem (normally mounted at /proc) which are used to control
24 the NFS server. This manual page describes all of these files.
25 The exportfs and mountd programs (part of the nfs-utils package) expect
27 to find this filesystem mounted at /proc/fs/nfsd or /proc/fs/nfs. If
28 it is not mounted, they will fall-back on 2.4 style functionality.
29 This involves accessing the NFS server via a systemcall. This system‐
30 call is scheduled to be removed after the 2.6 kernel series.
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33 The three files in the nfsd filesystem are:
34 exports
36 This file contains a list of filesystems that are currently
37 exported and clients that each filesystem is exported to,
38 together with a list of export options for that client/filesys‐
39 tem pair. This is similar to the /proc/fs/nfs/exports file in
40 2.4. One difference is that a client doesn't necessarily corre‐
41 spond to just one host. It can respond to a large collection of
42 hosts that are being treated identically.
43 Each line of the file contains a path name, a client name, and a
45 number of options in parentheses. Any space, tab, newline or
46 back-slash character in the path name or client name will be
47 replaced by a backslash followed by the octal ASCII code for
48 that character.
49 threads
52 This file represents the number of nfsd thread currently run‐
53 ning. Reading it will show the number of threads. Writing an
54 ASCII decimal number will cause the number of threads to be
55 changed (increased or decreased as necessary) to achieve that
56 number.
57 filehandle
60 This is a somewhat unusual file in that what is read from it
61 depends on what was just written to it. It provides a transac‐
62 tional interface where a program can open the file, write a
63 request, and read a response. If two separate programs open,
64 write, and read at the same time, their requests will not be
65 mixed up.
66 The request written to filehandle should be a client name, a
68 path name, and a number of bytes. This should be followed by a
69 newline, with white-space separating the fields, and octal quot‐
70 ing of special characters.
71 On writing this, the program will be able to read back a file‐
73 handle for that path as exported to the given client. The file‐
74 handle's length will be at most the number of bytes given.
75 The filehandle will be represented in hex with a leading '\x'.
77 The directory /proc/net/rpc in the procfs filesystem contains a number
79 of files and directories. The files contain statistics that can be
80 display using the nfsstat program. The directories contain information
81 about various caches that the NFS server maintains to keep track of
82 access permissions that different clients have for different filesys‐
83 tems. The caches are:
84 auth.unix.ip
87 This cache contains a mapping from IP address to the name of the
88 authentication domain that the ipaddress should be treated as
89 part of.
90 nfsd.export
93 This cache contains a mapping from directory and domain to
94 export options.
95 nfsd.fh
98 This cache contains a mapping from domain and a filesystem iden‐
99 tifier to a directory. The filesystem identifier is stored in
100 the filehandles and consists of a number indicating the type of
101 identifier and a number of hex bytes indicating the content of
102 the identifier.
103 Each directory representing a cache can hold from 1 to 3 files. They
106 are:
107 flush When a number of seconds since epoch (1 Jan 1970) is written to
109 this file, all entries in the cache that were last updated
110 before that file become invalidated and will be flushed out.
111 Writing a time in the future (in seconds since epoch) will flush
112 everything. This is the only file that will always be present.
113 content
116 This file, if present, contains a textual representation of ever
117 entry in the cache, one per line. If an entry is still in the
118 cache (because it is actively being used) but has expired or is
119 otherwise invalid, it will be presented as a comment (with a
120 leading hash character).
121 channel
124 This file, if present, acts a channel for request from the ker‐
125 nel-based nfs server to be passed to a user-space program for
126 handling.
127 When the kernel needs some information which isn't in the cache,
129 it makes a line appear in the channel file giving the key for
130 the information. A user-space program should read this, find
131 the answer, and write a line containing the key, an expiry time,
132 and the content. For example the kernel might make
133 nfsd 127.0.0.1
134 appear in the auth.unix.ip/content file. The user-space program
135 might then write
136 nfsd 127.0.0.1 1057206953 localhost
137 to indicate that 127.0.0.1 should map to localhost, at least for
138 now.
139 If the program uses select(2) or poll(2) to discover if it can
141 read from the channel then it will never see and end-of-file but
142 when all requests have been answered, it will block until
143 another request appears.
144 In the /proc filesystem there are 4 files that can be used to enabled
147 extra tracing of nfsd and related code. They are:
148 /proc/sys/sunrpc/nfs_debug
149 /proc/sys/sunrpc/nfsd_debug
150 /proc/sys/sunrpc/nlm_debug
151 /proc/sys/sunrpc/rpc_debug
152 They control tracing for the NFS client, the NFS server, the Network
153 Lock Manager (lockd) and the underlying RPC layer respectively. Deci‐
154 mal numbers can be read from or written to these files. Each number
155 represents a bit-pattern where bits that are set cause certain classes
156 of tracing to be enabled. Consult the kernel header files to find out
157 what number correspond to what tracing.
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161 nfsd(8), rpc.nfsd(8), exports(5), nfsstat(8), mountd(8) exportfs(8).
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165 NeilBrown
166 3 July 2003 nfsd(7)