1nfsd(7)                Miscellaneous Information Manual                nfsd(7)
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NAME

6       nfsd - special filesystem for controlling Linux NFS server
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SYNPOSIS

9       mount -t nfsd nfsd /proc/fs/nfsd
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DESCRIPTION

12       The  nfsd  filessytem  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.
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18       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.
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22       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.
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26       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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DETAILS

33       The three files in the nfsd filesystem are:
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35       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.
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44              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.
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50
51       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.
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58
59       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.
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67              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.
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72              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              handles length will be at most the number of bytes given.
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76              The filehandle will be represented in hex with a leading '\x'.
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78       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:
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85
86       auth.domain
87              This cache maps the name of a client (or domain) to an  internal
88              data  structure.   The  only access that is possible is to flush
89              the cache.
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92       auth.unix.ip
93              This cache contains a mapping from IP address to the name of the
94              authentication  domain  that  the ipaddress should be treated as
95              part of.
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97
98       nfsd.export
99              This cache contains a  mapping  from  directory  and  domain  to
100              export options.
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102
103       nfsd.fh
104              This cache contains a mapping from domain and a filesystem iden‐
105              tifier to a directory.   The filesystem identifier is stored  in
106              the  filehandles and consists of a number indicating the type of
107              identifier and a number of hex bytes indicating the  content  of
108              the identifier.
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110
111       Each  directory  representing a cache can hold from 1 to 3 files.  They
112       are:
113
114       flush  When a number of seconds since epoch (1 Jan 1970) is written  to
115              this  file,  all  entries  in  the  cache that were last updated
116              before that file become invalidated and  will  be  flushed  out.
117              Writing  1  will  flush  everything.  This is the only file that
118              will always be present.
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120
121       content
122              This file, if present, contains a textual representation of ever
123              entry  in  the cache, one per line.  If an entry is still in the
124              cache (because it is actively being used) but has expired or  is
125              otherwise  invalid,  it  will  be presented as a comment (with a
126              leading hash character).
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128
129       channel
130              This file, if present, acts a channel for request from the  ker‐
131              nel-based  nfs  server  to be passed to a user-space program for
132              handling.
133
134              When the kernel needs some information which isn't in the cache,
135              it  makes  a  line appear in the channel file giving the key for
136              the information.  A user-space program should  read  this,  find
137              the answer, and write a line containing the key, an expiry time,
138              and the content.  For example the kernel might make
139                   nfsd 127.0.0.1
140              appear in the auth.unix.ip/content file.  The user-space program
141              might then write
142                   nfsd 127.0.0.1 1057206953 localhost
143              to  indicate that 127.0.0.1 should map to localhost, atleast for
144              now.
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146              If the program uses select(2) or poll(2) to discover if  it  can
147              read from the channel then it will never see and end-of-file but
148              when all requests  have  been  answered,  it  will  block  until
149              another request appears.
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151
152       In  the  /proc filesystem there are 4 files that can be used to enabled
153       extra tracing of nfsd and related code.  They are:
154            /proc/sys/sunrpc/nfs_debug
155            /proc/sys/sunrpc/nfsd_debug
156            /proc/sys/sunrpc/nlm_debug
157            /proc/sys/sunrpc/rpc_debug
158       They control tracing for the NFS client, the NFS  server,  the  Network
159       Lock  Manager (lockd) and the underlying RPC layer respectively.  Deci‐
160       mal numbers can be read from or written to these  files.   Each  number
161       represents  a bit-pattern where bits that are set cause certain classes
162       of tracing to be enabled.  Consult the kernel header files to find  out
163       what number correspond to what tracing.
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SEE ALSO

167       rpc.nfsd(8), exports(5), nfsstat(8), mountd(8) exportfs(8).
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AUTHOR

171       NeilBrown
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175                                  3 July 2003                          nfsd(7)
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