xref: /freebsd/usr.sbin/sysconf/sysconf-sysctl.8 (revision b4a465e566a1850e232b454efe99e05c1ea93f67)

.\" Copyright (c) 2013-2026 Devin Teske <dteske@FreeBSD.org>
.\" Copyright (c) 2021-2026 Faraz Vahedi <kfv@FreeBSD.org>
.\"
.\" SPDX-License-Identifier: BSD-2-Clause
.\"
.Dd August 2, 2026
.Dt SYSCONF-SYSCTL 8
.Os
.Sh NAME
.Nm "sysconf sysctl"
.Nd configure boot-time sysctl.conf directives
.Sh SYNOPSIS
.Nm sysconf
.Cm sysctl
.Op Fl AcDeFinNqvVx
.Op Fl j Ar jail | Fl R Ar dir
.Op Fl f Ar file | Fl k Ar module
.Ar name Ns Op Ns Oo +|- Oc Ns = Ns Ar value
.Ar ...
.Nm sysconf
.Cm sysctl
.Op Fl ADeFnNqvV
.Op Fl f Ar file | Fl k Ar module
.Fl a
.Nm sysconf
.Cm sysctl
.Op Fl AaDinNq
.Fl d
.Op Ar name ...
.Nm sysconf
.Cm sysctl
.Op Fl E
.Op Fl k Ar module
.Fl l | L
.Sh DESCRIPTION
The
.Cm sysctl
target of
.Xr sysconf 8
reads and modifies
.Xr sysctl.conf 5
configuration.
Shared assignment syntax and options are documented in
.Xr sysconf 8 ;
multi-file write policy in
.Xr sysconf-targets 8 .
.Pp
The stock file list is
.Pa /etc/sysctl.conf ,
.Pa /etc/sysctl.conf.local ,
then
.Pa /etc/sysctl.kld.d/ Ns Ar module Ns Pa .conf
when
.Fl k Ar module
is given
.Pq applied by Xr rc.subr 8 when the module loads .
.Pp
Values are quoted on write only when the value requires it
.Pq embedded whitespace .
.Pp
When writing to the running system,
each
.Ar name Ns = Ns Ar value
is validated against the kernel's sysctl tree first.
An OID that cannot be set at run time
.Pq non-leaf, read-only, or loader-only tunable
is reported and skipped,
while the remaining assignments are still applied.
In particular,
a loader-only tunable is reported as requiring the
.Cm loader
target instead
.Pq see Xr sysconf-loader 8 .
Numeric values are also checked against the OID's
.Dv CTLTYPE
.Po
.Dv CTLTYPE_INT ,
.Dv CTLTYPE_U64 ,
and the other integer widths
.Pc
so an overflowing or non-numeric assignment cannot land in
.Xr sysctl.conf 5
and fail
.Pq or apply truncated
when
.Xr sysctl 8
loads the file at boot.
.Pp
An unknown OID
.Pq often from a module that is not yet loaded
is reported with a warning but still written,
matching how
.Xr init 8
treats such lines in
.Xr sysctl.conf 5 ;
.Fl i
and
.Fl q
suppress that warning.
Validation is skipped entirely under
.Fl R ,
where the target system's kernel is not the running kernel.
.Pp
.Fl d
descriptions for this target come from the running kernel
.Pq as with Xr sysctl 8 Fl d ,
not from a defaults file.
.Sh FILES
.Bl -tag -width "/etc/sysctl.conf.local" -compact
.It Pa /etc/sysctl.conf
Write target for new directives.
.It Pa /etc/sysctl.conf.local
Site-local overrides.
.It Pa /etc/sysctl.kld.d/
Module-specific drop-ins
.Pq see Fl k .
.El
.Sh EXAMPLES
.Dl sysconf sysctl kern.maxfiles=65536
.Dl sysconf sysctl -F vfs.usermount
.Dl sysconf sysctl -d kern.maxfiles
.Dl sysconf sysctl -L
.Dl sysconf sysctl -LE
.Dl sysconf sysctl -k ipfw net.inet.ip.fw.verbose=1
.Dl sysconf -x sysctl vfs.usermount
.Dl sysconf -j www sysctl kern.ipc.somaxconn=1024
.Pp
An overflowing assignment is refused before the file is touched
.Pq here an integer OID given a value beyond INT_MAX :
.Pp
.Dl sysconf sysctl security.bsd.see_other_uids=99999999999
.Sh SEE ALSO
.Xr sysctl.conf 5 ,
.Xr sysconf 8 ,
.Xr sysconf-loader 8 ,
.Xr sysconf-targets 8 ,
.Xr sysctl 8
.Sh HISTORY
The
.Nm sysconf
utility first appeared in
.Fx 16.0 .
.Sh AUTHORS
.An Devin Teske Aq Mt dteske@FreeBSD.org
.An Faraz Vahedi Aq Mt kfv@FreeBSD.org