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nfsd(7) Miscellaneous Information Manual nfsd(7)
NAME
nfsd - special filesystem for controlling Linux NFS server
SYNPOSIS
mount -t nfsd nfsd /proc/fs/nfsd
DESCRIPTION
The nfsd filesystem is a special filesystem which provides access to the Linux NFS server.
The filesystem consists of a single directory which contains a number of files. These
files are actually gateways into the NFS server. Writing to them can affect the server.
Reading from them can provide information about the server.
This file system is only available in Linux 2.6 and later series kernels (and in the later
parts of the 2.5 development series leading up to 2.6). This man page does not apply to
2.4 and earlier.
As well as this filesystem, there are a collection of files in the procfs filesystem (nor-
mally mounted at /proc) which are used to control the NFS server. This manual page
describes all of these files.
The exportfs and mountd programs (part of the nfs-utils package) expect to find this
filesystem mounted at /proc/fs/nfsd or /proc/fs/nfs. If it is not mounted, they will
fall-back on 2.4 style functionality. This involves accessing the NFS server via a sys-
temcall. This systemcall is scheduled to be removed after the 2.6 kernel series.
DETAILS
The three files in the nfsd filesystem are:
exports
This file contains a list of filesystems that are currently exported and clients
that each filesystem is exported to, together with a list of export options for
that client/filesystem pair. This is similar to the /proc/fs/nfs/exports file in
2.4. One difference is that a client doesn't necessarily correspond to just one
host. It can respond to a large collection of hosts that are being treated identi-
cally.
Each line of the file contains a path name, a client name, and a number of options
in parentheses. Any space, tab, newline or back-slash character in the path name
or client name will be replaced by a backslash followed by the octal ASCII code for
that character.
threads
This file represents the number of nfsd thread currently running. Reading it will
show the number of threads. Writing an ASCII decimal number will cause the number
of threads to be changed (increased or decreased as necessary) to achieve that num-
ber.
filehandle
This is a somewhat unusual file in that what is read from it depends on what was
just written to it. It provides a transactional interface where a program can open
the file, write a request, and read a response. If two separate programs open,
write, and read at the same time, their requests will not be mixed up.
The request written to filehandle should be a client name, a path name, and a num-
ber of bytes. This should be followed by a newline, with white-space separating
the fields, and octal quoting of special characters.
On writing this, the program will be able to read back a filehandle for that path
as exported to the given client. The filehandle's length will be at most the num-
ber of bytes given.
The filehandle will be represented in hex with a leading '\x'.
The directory /proc/net/rpc in the procfs filesystem contains a number of files and direc-
tories. The files contain statistics that can be display using the nfsstat program. The
directories contain information about various caches that the NFS server maintains to keep
track of access permissions that different clients have for different filesystems. The
caches are:
auth.unix.ip
This cache contains a mapping from IP address to the name of the authentication
domain that the ipaddress should be treated as part of.
nfsd.export
This cache contains a mapping from directory and domain to export options.
nfsd.fh
This cache contains a mapping from domain and a filesystem identifier to a direc-
tory. The filesystem identifier is stored in the filehandles and consists of a
number indicating the type of identifier and a number of hex bytes indicating the
content of the identifier.
Each directory representing a cache can hold from 1 to 3 files. They are:
flush When a number of seconds since epoch (1 Jan 1970) is written to this file, all
entries in the cache that were last updated before that file become invalidated and
will be flushed out. Writing a time in the future (in seconds since epoch) will
flush everything. This is the only file that will always be present.
content
This file, if present, contains a textual representation of ever entry in the
cache, one per line. If an entry is still in the cache (because it is actively
being used) but has expired or is otherwise invalid, it will be presented as a com-
ment (with a leading hash character).
channel
This file, if present, acts a channel for request from the kernel-based nfs server
to be passed to a user-space program for handling.
When the kernel needs some information which isn't in the cache, it makes a line
appear in the channel file giving the key for the information. A user-space pro-
gram should read this, find the answer, and write a line containing the key, an
expiry time, and the content. For example the kernel might make
nfsd 127.0.0.1
appear in the auth.unix.ip/content file. The user-space program might then write
nfsd 127.0.0.1 1057206953 localhost
to indicate that 127.0.0.1 should map to localhost, at least for now.
If the program uses select(2) or poll(2) to discover if it can read from the chan-
nel then it will never see and end-of-file but when all requests have been
answered, it will block until another request appears.
In the /proc filesystem there are 4 files that can be used to enabled extra tracing of
nfsd and related code. They are:
/proc/sys/sunrpc/nfs_debug
/proc/sys/sunrpc/nfsd_debug
/proc/sys/sunrpc/nlm_debug
/proc/sys/sunrpc/rpc_debug
They control tracing for the NFS client, the NFS server, the Network Lock Manager (lockd)
and the underlying RPC layer respectively. Decimal numbers can be read from or written to
these files. Each number represents a bit-pattern where bits that are set cause certain
classes of tracing to be enabled. Consult the kernel header files to find out what number
correspond to what tracing.
SEE ALSO
rpc.nfsd(8), exports(5), nfsstat(8), mountd(8) exportfs(8).
AUTHOR
NeilBrown
3 July 2003 nfsd(7)
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