---
name: "tc-hfsc"
section: "8"
platform: "linux"
package: "iproute2"
version: "7.3.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/tc-hfsc"
---

# tc-hfsc(8)

Hierarchical Fair Service Curve's control under linux

## NAME

HFSC - Hierarchical Fair Service Curve's control under linux

## SYNOPSIS

```
tc qdisc add ... hfsc [ default CLASSID ]
tc class add ... hfsc [ [ rt SC ] [ ls SC ] | [ sc SC ] ] [ ul SC ]
rt : realtime service curve
ls : linkshare service curve
sc : rt+ls service curve
ul : upperlimit service curve
• at least one of rt, ls or sc must be specified
• ul can only be specified with ls or sc
```

- SC := \[ \[ **m1** BPS \] **d** SEC \] **m2** BPS

  **m1** : slope of the first segment **d**  : x-coordinate of intersection **m2** : slope of the second segment

- SC := \[ \[ **umax** BYTE \] **dmax** SEC \] **rate** BPS

  **umax** : maximum unit of work **dmax** : maximum delay **rate** : rate

For description of BYTE, BPS and SEC - please see **UNITS** section of [**tc**(8)](/tc/8.md).

## DESCRIPTION (qdisc)

HFSC qdisc has only one optional parameter - **default**. CLASSID specifies the minor part of the default classid, where packets not classified by other means (e.g. u32 filter, CLASSIFY target of iptables) will be enqueued. If **default** is not specified, unclassified packets will be dropped.

## DESCRIPTION (class)

HFSC class is used to create a class hierarchy for HFSC scheduler. For explanation of the algorithm, and the meaning behind **rt**, **ls**, **sc** and **ul** service curves - please refer to [**tc-hfsc**(7)](/tc-hfsc/7.md).

As you can see in **SYNOPSIS**, service curve (SC) can be specified in two ways. Either as maximum delay for certain amount of work, or as a bandwidth assigned for certain amount of time. Obviously, **m1** is simply **umax**/**dmax**.

Both **m2** and **rate** are mandatory. If you omit other parameters, you will specify linear service curve.

## SEE ALSO

[**tc**(8)](/tc/8.md), [**tc-hfsc**(7)](/tc-hfsc/7.md), [**tc-stab**(8)](/tc-stab/8.md)

Please direct bugreports and patches to: \<netdev@vger.kernel.org\>

## AUTHOR

Manpage created by Michal Soltys (soltys@ziu.info)