.\"
.\" SPDX-License-Identifier: BSD-2-Clause
.\"
.\" Copyright (c) 2020, 2026 Devin Teske <dteske@FreeBSD.org>
.\"
.Dd September 4, 2026
.Dt NFSDTOP 8
.Os
.Sh NAME
.Nm nfsdtop
.Nd display top-like NFS server I/O statistics
.Sh SYNOPSIS
.Nm
.Op Fl aDdhnoqRrvw
.Op Fl b | Fl j | Fl J
.Op Fl C Ar ip
.Op Fl c | Fl g | Fl u
.Op Fl G Ar group
.Op Fl I Ar file
.Op Fl i Ar sec
.Op Fl N Ar num
.Op Fl P Ar file
.Op Fl p Ar file
.Op Fl U Ar user
.Sh DESCRIPTION
The
.Nm
utility uses
.Xr dtrace 1
to display a periodically updated table of NFS
server read and write activity.
Statistics are taken from the
.Xr nfsd 8
read and write paths
.Pq Fn nfsrvd_read , Fn nfsvno_read , Fn nfsrvd_write , and Fn nfsvno_write
and coalesced by a chosen
.Em view .
.Pp
Only the root user or users with
.Xr dtrace 1
privileges can run this command.
.Pp
A view selects the first column of the display.
The default is the user view
.Pq Ql Fl u ,
where each row is a UID
.Pq or user name .
The group view
.Pq Ql Fl g
and client view
.Pq Ql Fl c
instead coalesce by GID or IPv4 client address.
Without
.Ql Fl j ,
the last of
.Ql Fl c ,
.Ql Fl g ,
or
.Ql Fl u
wins.
.Pp
UIDs, GIDs, and IPv4 addresses shown in a view are taken from NFS client
credentials and addresses on the
.Xr nfsd 8
paths.
They often cannot be resolved on the nfsd host, so
.Nm
does not use
.Xr getent 1
to name them as traffic is sampled; that lookup would likely be useless.
The map files described in
.Sx FILES
supply those names.
Command-line filters are different.
A name given to
.Ql Fl U ,
.Ql Fl G ,
or
.Ql Fl C
is resolved once, first from the same map files and then via
.Xr getent 1
or
.Xr host 1 ,
so the resulting UID, GID, or address can be compiled into the
.Xr dtrace 1
predicates.
.Pp
Each interval prints a header followed by a
.Ql total
row and per-key rows sorted by combined read and write volume.
Columns are the view key,
combined TOTAL,
WRITE(IN),
an optional bar,
and READ(OUT).
Values are humanized bandwidth
.Pq bytes per second
unless
.Ql Fl b
is given.
When standard output is a terminal,
the screen is redrawn in place and
.Dv SIGWINCH
resizes the layout.
.Sh OPTIONS
.Bl -tag -width "-I file"
.It Fl a
Always enable color,
even when standard output is not a terminal.
.It Fl b
Show bytes transferred during the interval instead of bandwidth.
Cannot be combined with
.Ql Fl j
or
.Ql Fl J .
.It Fl C Ar ip
Client filter.
Only count I/O for the given IPv4 address or hostname
.Pq IPv4 only .
A hostname given here is resolved once from the IP map
.Pq see Fl I
or
.Xr host 1 .
.It Fl c
View read/write activity by client.
.It Fl D
Enable debugger.
Print raw
.Xr dtrace 1
output and additional post-processor diagnostics.
.It Fl d
Debug.
Print the generated
.Xr dtrace 1
script to standard output and exit.
.It Fl G Ar group
Group filter.
Only count I/O for the given group name or GID.
A name given here is resolved once from the group map
.Pq see Fl P
or
.Xr getent 1 .
.It Fl g
View read/write activity by group.
.It Fl h
Print usage statement and exit.
.It Fl I Ar file
IP map file for naming observed client addresses
.Pq see DESCRIPTION .
Default
.Pa .nfsd.hosts
in the current directory.
Each non-comment line is an IPv4 address followed by a hostname.
.It Fl i Ar sec
Set interval seconds.
Default
.Ql 2.0 .
Must be at least 0.001.
.It Fl J
Output JSON for the client, group, and user views.
Same as
.Ql Fl jcgu .
.It Fl j
Output JSON formatted data.
Each interval emits one object for the view total and one object per key.
Objects contain
.Li time ,
.Li ident ,
.Li total_bytes ,
.Li total_rate ,
.Li read_bytes ,
.Li read_rate ,
.Li write_bytes ,
and
.Li write_rate .
.It Fl N Ar num
Perform
.Ar num
samples and exit.
.It Fl n
Do not map observed UIDs, GIDs, or IPs through the map files.
.It Fl o
Force non-console output.
Disable screen redraw and color.
.It Fl P Ar file
Group map file for naming observed GIDs
.Pq see DESCRIPTION .
Default
.Pa .nfsd.group
in the current directory.
Format is
.Xr group 5 .
.It Fl p Ar file
User map file for naming observed UIDs
.Pq see DESCRIPTION .
Default
.Pa .nfsd.passwd
in the current directory.
Format is
.Xr passwd 5 .
.It Fl q
Quiet.
Hide informational messages.
.It Fl R
Redact potentially sensitive information.
User, group, and client names that are not well-known system accounts are
replaced with random strings of the same length.
May also be enabled by setting
.Ev NFSDTOP_REDACT
in the environment.
.It Fl r
Raw view.
Do not format output of
.Xr dtrace 1 .
.It Fl U Ar user
User filter.
Only count I/O for the given user name or UID.
A name given here is resolved once from the user map
.Pq see Fl p
or
.Xr getent 1 .
.It Fl u
View read/write activity by user
.Pq default .
.It Fl v
Print version and exit.
.It Fl w
Wide view.
Maximize width of the first column.
.El
.Sh ENVIRONMENT
.Bl -tag -width NFSDTOP_REDACT
.It Ev NFSDTOP_REDACT
If set to a non-empty value, enable redaction as with
.Ql Fl R .
.El
.Sh FILES
These files map identifiers from observed NFS traffic to names.
.Xr getent 1
on the nfsd host is not used for that translation.
.Pp
.Bl -tag -width ".nfsd.passwd" -compact
.It Pa .nfsd.passwd
Default user map
.Pq Ql Fl p ,
looked up in the current directory.
.It Pa .nfsd.group
Default group map
.Pq Ql Fl P ,
looked up in the current directory.
.It Pa .nfsd.hosts
Default IP map
.Pq Ql Fl I ,
looked up in the current directory.
.El
.Sh EXIT STATUS
.Ex -std
.Sh EXAMPLES
Display per-user NFS
server I/O, updated every two seconds:
.Bd -literal -offset indent
nfsdtop
.Ed
.Pp
View activity by NFS client:
.Bd -literal -offset indent
nfsdtop -c
.Ed
.Pp
Restrict the group view to
.Ql wheel :
.Bd -literal -offset indent
nfsdtop -g -G wheel
.Ed
.Pp
Count only I/O from one client and show bytes instead of bandwidth:
.Bd -literal -offset indent
nfsdtop -c -C 192.0.2.10 -b
.Ed
.Pp
Emit one JSON sample for all views and exit:
.Bd -literal -offset indent
nfsdtop -J -N 1
.Ed
.Pp
Print the generated DTrace script without running it:
.Bd -literal -offset indent
nfsdtop -d
.Ed
.Sh SEE ALSO
.Xr dtrace 1 ,
.Xr dwatch 1 ,
.Xr getent 1 ,
.Xr nfsstat 1 ,
.Xr group 5 ,
.Xr passwd 5 ,
.Xr gstat 8 ,
.Xr iostat 8 ,
.Xr nfsd 8
.Sh HISTORY
The
.Nm
utility first appeared in
.Fx 16.0 .
.Sh AUTHORS
.An Devin Teske Aq Mt dteske@FreeBSD.org
.Sh BUGS
The client view and
.Ql Fl C
filter support IPv4 only.