---
name: "sysconf-sysctl"
section: "8"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd"]
url: "https://new.carta.tech/sysconf-sysctl"
---

# sysconf-sysctl(8)

configure boot-time sysctl.conf directives

## NAME

**sysconf sysctl** – configure boot-time sysctl.conf directives

## SYNOPSIS

**sysconf** **sysctl** \[**-AcDeFinNqvVx**\] \[**-j** *jail* \| **-R** *dir*\] \[**-f** *file* \| **-k** *module*\] *name*\[\[+\|-\]=*value*\] *...*

**sysconf** **sysctl** \[**-ADeFnNqvV**\] \[**-f** *file* \| **-k** *module*\] **-a**

**sysconf** **sysctl** \[**-AaDinNq**\] **-d** \[*name* *...*\]

**sysconf** **sysctl** \[**-E**\] \[**-k** *module*\] **-l** \| **-L**

## DESCRIPTION

The **sysctl** target of [sysconf(8)](/sysconf/8.md) reads and modifies [sysctl.conf(5)](/sysctl.conf/5.md) configuration. Shared assignment syntax and options are documented in [sysconf(8)](/sysconf/8.md); multi-file write policy in [sysconf-targets(8)](/sysconf-targets/8.md).

The stock file list is */etc/sysctl.conf*, */etc/sysctl.conf.local*, then */etc/sysctl.kld.d/**module**.conf* when **-k** *module* is given (applied by [rc.subr(8)](/rc.subr/8.md) when the module loads).

Values are quoted on write only when the value requires it (embedded whitespace).

When writing to the running system, each *name*=*value* is validated against the kernel's sysctl tree first. An OID that cannot be set at run time (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 **loader** target instead (see [sysconf-loader(8)](/sysconf-loader/8.md)). Numeric values are also checked against the OID's CTLTYPE( CTLTYPE\_INT, CTLTYPE\_U64, and the other integer widths) so an overflowing or non-numeric assignment cannot land in [sysctl.conf(5)](/sysctl.conf/5.md) and fail (or apply truncated) when [sysctl(8)](/sysctl/8.md) loads the file at boot.

An unknown OID (often from a module that is not yet loaded) is reported with a warning but still written, matching how [init(8)](/init/8.md) treats such lines in [sysctl.conf(5)](/sysctl.conf/5.md); **-i** and **-q** suppress that warning. Validation is skipped entirely under **-R**, where the target system's kernel is not the running kernel.

**-d** descriptions for this target come from the running kernel (as with [sysctl(8)](/sysctl/8.md) **-d**), not from a defaults file.

## FILES

- */etc/sysctl.conf*

  Write target for new directives.

- */etc/sysctl.conf.local*

  Site-local overrides.

- */etc/sysctl.kld.d/*

  Module-specific drop-ins (see **-k**).

## EXAMPLES

```
sysconf sysctl kern.maxfiles=65536
```

```
sysconf sysctl -F vfs.usermount
```

```
sysconf sysctl -d kern.maxfiles
```

```
sysconf sysctl -L
```

```
sysconf sysctl -LE
```

```
sysconf sysctl -k ipfw net.inet.ip.fw.verbose=1
```

```
sysconf -x sysctl vfs.usermount
```

```
sysconf -j www sysctl kern.ipc.somaxconn=1024
```

An overflowing assignment is refused before the file is touched (here an integer OID given a value beyond INT\_MAX):

```
sysconf sysctl security.bsd.see_other_uids=99999999999
```

## SEE ALSO

[sysctl.conf(5)](/sysctl.conf/5.md), [sysconf(8)](/sysconf/8.md), [sysconf-loader(8)](/sysconf-loader/8.md), [sysconf-targets(8)](/sysconf-targets/8.md), [sysctl(8)](/sysctl/8.md)

## HISTORY

The **sysconf** utility first appeared in FreeBSD 16.0.

## AUTHORS

Devin Teske ⟨*dteske@FreeBSD.org*⟩ Faraz Vahedi ⟨*kfv@FreeBSD.org*⟩