---
name: "kenv"
section: "2freebsd"
platform: "linux"
package: "freebsd-manpages"
version: "12.2-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/kenv/2freebsd"
---

# kenv(2freebsd)

kernel environment

## NAME

**kenv** – kernel environment

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<kenv.h\>**

*int*\

**kenv**(*int action*, *const char \*name*, *char \*value*, *int len*);

## DESCRIPTION

The **kenv**() system call manipulates kernel environment variables. It supports the well known userland actions of getting, setting and unsetting environment variables, as well as the ability to dump all of the entries in the kernel environment.

The *action* argument can be one of the following:

- KENV\_GET

  Get the *value* of the variable with the given *name*. The size of the *value* buffer is given by *len*, which should be at least KENV\_MVALLEN + 1 bytes to avoid truncation and to ensure NUL termination.

- KENV\_SET

  Set or add a variable. The *name* and *value* are limited to KENV\_MNAMELEN and KENV\_MVALLEN characters, respectively (not including the NUL terminator.) The *len* argument indicates the length of the *value* and must include the NUL terminator. This option is only available to the superuser.

- KENV\_UNSET

  Unset the variable with the given *name*. The *value* and *len* arguments are ignored. This option is only available to the superuser.

- KENV\_DUMP

  Dump as much of the kernel environment as will fit in *value*, whose size is given in *len*. If *value* is NULL, **kenv**() will return the number of bytes required to copy out the entire environment. The *name* is ignored.

## RETURN VALUES

The **kenv**() system call returns 0 if successful in the case of KENV\_SET and KENV\_UNSET, and the number of bytes copied into *value* in the case of KENV\_DUMP and KENV\_GET. If an error occurs, a value of -1 is returned and the global variable *errno* is set to indicate the error.

## ERRORS

The **kenv**() system call will fail if:

- \[EINVAL\]

  The *action* argument is not a valid option, or the length of the *value* is less than 1 for a KENV\_SET.

- \[ENOENT\]

  No value could be found for *name* for a KENV\_GET or KENV\_UNSET.

- \[EPERM\]

  A user other than the superuser attempted to set or unset a kernel environment variable.

- \[EFAULT\]

  A bad address was encountered while attempting to copy in user arguments or copy out value(s).

- \[ENAMETOOLONG\]

  The *name* or the *value* is longer than KENV\_MNAMELEN or KENV\_MVALLEN characters, respectively, or *len* did not include the NUL terminator for a KENV\_SET.

## SEE ALSO

[kenv(1)](/kenv/1.md)

## AUTHORS

This manual page was written by Chad David ⟨*davidc@FreeBSD.org*⟩.

The **kenv**() system call was written by Maxime Henrion ⟨*mux@FreeBSD.org*⟩.