---
name: "rctl"
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/rctl"
---

# rctl(8)

display and update resource limits database

## NAME

**rctl** – display and update resource limits database

## SYNOPSIS

**rctl** \[**-h**\] \[**-n**\] \[*filter* *...*\]

**rctl** **-a** *rule* *...*

**rctl** **-l** \[**-h**\] \[**-n**\] *filter* *...*

**rctl** **-r** *filter* *...*

**rctl** **-u** \[**-h**\] *filter* *...*

## DESCRIPTION

When called without options, the **rctl** command writes currently defined RCTL rules to standard output.

If a *filter* argument is specified, only rules matching the filter are displayed. The options are as follows:

- **-a** *rule*

  Add *rule* to the RCTL database.

- **-l** *filter*

  Display rules applicable to the process defined by *filter*. Note that this is different from showing the rules when called without any options, as it shows not just the rules with subject equal to that of process, but also rules for the user, jail, and login class applicable to the process.

- **-r** *filter*

  Remove rules matching *filter* from the RCTL database.

- **-u** *filter*

  Display resource utilization for a subject( **process**, **user**, **loginclass** or **jail**) matching the *filter*.

- **-h**

  "Human-readable" output. Use unit suffixes: Byte, Kilobyte, Megabyte, Gigabyte, Terabyte and Petabyte.

- **-n**

  Display user IDs numerically rather than converting them to a user name.

Modifying rules affects all currently running and future processes matching the rule.

## RULE SYNTAX

Syntax for a rule is subject:subject-id:resource:action=amount/per.

- subject

  defines the kind of entity the rule applies to. It can be either **process**, **user**, **loginclass**, or **jail**.

- subject-id

  identifies the *subject*. It can be a process ID, user name, numerical user ID, login class name from [login.conf(5)](/login.conf/5.md), or jail name.

- resource

  identifies the resource the rule controls. See the RESOURCES section below for details.

- action

  defines what will happen when a process exceeds the allowed *amount*. See the ACTIONS section below for details.

- amount

  defines how much of the resource a process can use before the defined *action* triggers. Resources which limit bytes may use prefixes from [expand\_number(3)](/expand_number/3.md).

- per

  defines what entity the *amount* gets accounted for. For example, rule "loginclass:users:vmemoryuse:deny=100M/process" means that each process of any user belonging to login class "users" may allocate up to 100MB of virtual memory. Rule "loginclass:users:vmemoryuse:deny=100M/user" would mean that for each user belonging to the login class "users", the sum of virtual memory allocated by all the processes of that user will not exceed 100MB. Rule "loginclass:users:vmemoryuse:deny=100M/loginclass" would mean that the sum of virtual memory allocated by all processes of all users belonging to that login class will not exceed 100MB.

A valid rule has all those fields specified, except for *per*, which defaults to the value of *subject*.

A filter is a rule for which one of more fields other than *per* is left empty. For example, a filter that matches every rule could be written as ":::=/", or, in short, ":". A filter that matches all the login classes would be "loginclass:". A filter that matches all defined rules for **maxproc** resource would be "::maxproc".

## SUBJECTS

| | |
| --- | --- |
| **process** | numerical Process ID |
| **user** | user name or numerical User ID |
| **loginclass** | login class from |
| **jail** | jail name |

## RESOURCES

| | |
| --- | --- |
| **cputime** | CPU time, in seconds |
| **datasize** | data size, in bytes |
| **stacksize** | stack size, in bytes |
| **coredumpsize** | core dump size, in bytes |
| **memoryuse** | resident set size, in bytes |
| **memorylocked** | locked memory, in bytes |
| **maxproc** | number of processes |
| **openfiles** | file descriptor table size |
| **vmemoryuse** | address space limit, in bytes |
| **pseudoterminals** | number of PTYs |
| **swapuse** | swap space that may be reserved or used, in bytes |
| **nthr** | number of threads |
| **msgqqueued** | number of queued SysV messages |
| **msgqsize** | SysV message queue size, in bytes |
| **nmsgq** | number of SysV message queues |
| **nsem** | number of SysV semaphores |
| **nsemop** | number of SysV semaphores modified in a single [semop(2)](/semop/2.md) call |
| **nshm** | number of SysV shared memory segments |
| **shmsize** | SysV shared memory size, in bytes |
| **wallclock** | wallclock time, in seconds |
| **pcpu** | %CPU, in percents of a single CPU core |
| **readbps** | filesystem reads, in bytes per second |
| **writebps** | filesystem writes, in bytes per second |
| **readiops** | filesystem reads, in operations per second |
| **writeiops** | filesystem writes, in operations per second |

## ACTIONS

| | |
| --- | --- |
| **deny** | deny the allocation; not supported for |
| **log** | log a warning to the console |
| **devctl** | send notification to |
| sig\* e.g. |
| **throttle** | slow down process execution; only supported for |

Not all actions are supported for all resources. Attempting to add a rule with an action not supported by a given resource will result in error.

## EXIT STATUS

The **rctl** utility exits 0 on success, and \>0 if an error occurs.

## EXAMPLES

Prevent user "joe" from allocating more than 1GB of virtual memory:

```
rctl -a user:joe:vmemoryuse:deny=1g
```

Remove all RCTL rules:

```
rctl -r :
```

Display resource utilization information for jail named "www":

```
rctl -hu jail:www
```

Display all the rules applicable to process with PID 512:

```
rctl -l process:512
```

Display all rules:

```
rctl
```

Display all rules matching user "joe":

```
rctl user:joe
```

Display all rules matching login classes:

```
rctl loginclass:
```

## SEE ALSO

[cpuset(1)](/cpuset/1.md), [rctl(4)](/rctl/4.md), [rctl.conf(5)](/rctl.conf/5.md)

## HISTORY

The **rctl** command appeared in FreeBSD 9.0.

## AUTHORS

The **rctl** was developed by Edward Tomasz Napierala ⟨*trasz@FreeBSD.org*⟩ under sponsorship from the FreeBSD Foundation.

## BUGS

Limiting **memoryuse** may kill the machine due to thrashing.

The **readiops** and **writeiops** counters are only approximations. Like **readbps** and **writebps**, they are calculated in the filesystem layer, where it is difficult or even impossible to observe actual disk device operations.

The **writebps** and **writeiops** resources generally account for writes to the filesystem cache, not to actual devices.