# man > HFSC(8)

[_HFSC_(8)](https://www.chedong.com/phpMan.php/man/HFSC/8/markdown)                                         Linux                                        [_HFSC_(8)](https://www.chedong.com/phpMan.php/man/HFSC/8/markdown)

## 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)](https://www.chedong.com/phpMan.php/man/tc/8/markdown).

**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 tar‐
       get 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 al‐
       gorithm,  and  the  meaning  behind  **rt**,  **ls**,  **sc  **and  **ul  **service  curves - please refer to
       [**tc-hfsc**(7)](https://www.chedong.com/phpMan.php/man/tc-hfsc/7/markdown).

       As you can see in **SYNOPSIS**, service curve (SC) can be specified in two ways. Either as  maxi‐
       mum  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)](https://www.chedong.com/phpMan.php/man/tc/8/markdown), [**tc-hfsc**(7)](https://www.chedong.com/phpMan.php/man/tc-hfsc/7/markdown), [**tc-stab**(8)](https://www.chedong.com/phpMan.php/man/tc-stab/8/markdown)

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

## AUTHOR
       Manpage created by Michal Soltys (<soltys@ziu.info>)

iproute2                                   31 October 2011                                   [_HFSC_(8)](https://www.chedong.com/phpMan.php/man/HFSC/8/markdown)