---
name: "rctl_add_rule"
section: "2"
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/rctl_add_rule"
---

# rctl\_add\_rule(2)

manipulate and query the resource limits database

## NAME

**rctl\_add\_rule**, **rctl\_get\_limits**, **rctl\_get\_racct**, **rctl\_get\_rules**, **rctl\_remove\_rule** – manipulate and query the resource limits database

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<sys/rctl.h\>**

*int*\

**rctl\_add\_rule**(*const char \*inbufp*, *size\_t inbuflen*, *char \*outbufp*, *size\_t outbuflen*);

*int*\

**rctl\_get\_limits**(*const char \*inbufp*, *size\_t inbuflen*, *char \*outbufp*, *size\_t outbuflen*);

*int*\

**rctl\_get\_racct**(*const char \*inbufp*, *size\_t inbuflen*, *char \*outbufp*, *size\_t outbuflen*);

*int*\

**rctl\_get\_rules**(*const char \*inbufp*, *size\_t inbuflen*, *char \*outbufp*, *size\_t outbuflen*);

*int*\

**rctl\_remove\_rule**(*const char \*inbufp*, *size\_t inbuflen*, *char \*outbufp*, *size\_t outbuflen*);

## DESCRIPTION

These system calls are used to manipulate and query the resource limits database. For all functions, *inbuflen* refers to the length of the buffer pointed to by *inbufp* and *outbuflen* refers to the length of the buffer pointed to by *outbufp*.

The **rctl\_add\_rule**() function adds the rule pointed to by *inbufp* to the resource limits database. The *outbufp* and *outbuflen* arguments are unused. Rule format is as described in [rctl(8)](/rctl/8.md), with exceptions noted in the RULES AND FILTERS section.

The **rctl\_get\_limits**() function returns in *outbufp* a comma-separated list of rules that apply to the process that matches the filter specified in *inbufp*. This includes rules with a subject of the process itself as well as rules with a different subject (such as user or loginclass) that apply to the process.

The **rctl\_get\_racct**() function returns resource usage information for a given subject. The subject is specified by passing a filter in *inbufp*. Filter syntax is as described in [rctl(8)](/rctl/8.md), with exceptions noted in the RULES AND FILTERS section. A comma-separated list of resources and the amount used of each by the specified subject is returned in *outbufp*. The resource and amount is formatted as "resource=amount".

The **rctl\_get\_rules**() function returns in *outbufp* a comma-separated list of rules from the resource limits database that match the filter passed in *inbufp*. Filter syntax is as described in [rctl(8)](/rctl/8.md), with exceptions noted in the RULES AND FILTERS section. A filter of *::* may be passed to return all rules.

The **rctl\_remove\_rule**() function removes all rules matching the filter passed in *inbufp* from the resource limits database. Filter syntax is as described in [rctl(8)](/rctl/8.md), with exceptions noted in the RULES AND FILTERS section. *outbufp* and *outbuflen* are unused.

## RULES AND FILTERS

This section explains how the rule and filter format described in [rctl(8)](/rctl/8.md) differs from the format passed to the system calls themselves. The rctl tool provides several conveniences that the system calls do not. When using the system call:

- The subject must be fully specified. For example, abbreviating ‘user’ to ‘u’ is not acceptable.

- User and group IDs must be numeric. For example, ‘root’ must be expressed as ‘0’.

- Units are not permitted on resource amounts. For example, a quantity of 1024 bytes must be expressed as ‘1024’ and not ‘1k’.

## RETURN VALUES

The **rctl\_add\_rule()** function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

## ERRORS

The rctl system calls may fail if:

- \[ENOSYS\]

  RACCT/RCTL support is not present in the kernel or the *kern.racct.enable* sysctl is 0.

- \[EINVAL\]

  The rule or filter passed in *inbufp* is invalid.

- \[EPERM\]

  User has insufficient privileges to carry out the requested operation.

- \[E2BIG\]

  *inbufp* or *outbufp* are too large.

- \[ESRCH\]

  No process matched the provided rule or filter.

- \[ENAMETOOLONG\]

  The loginclass or jail name specified is too long.

- \[ERANGE\]

  The rule amount is outside of the allowable range or *outbufp* is too small.

- \[EOPNOTSUPP\]

  The requested operation is not supported for the given rule or filter.

- \[EFAULT\]

  *inbufp* or *outbufp* refer to invalid addresses.

## SEE ALSO

[rctl(8)](/rctl/8.md)

## HISTORY

The rctl family of system calls appeared in FreeBSD 9.0.

## AUTHORS

The rctl system calls were developed by Edward Tomasz Napierala ⟨*trasz@FreeBSD.org*⟩ under sponsorship from the FreeBSD Foundation. This manual page was written by Eric Badger ⟨*badger@FreeBSD.org*⟩.