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NAME | SYNOPSIS | DESCRIPTION | ALGORITHM | PARAMETERS | OUTPUT | SEE ALSO | AUTHORS | COLOPHON |
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PBFIFO(8) Linux PBFIFO(8)
pfifo - Packet limited First In, First Out queue
bfifo - Byte limited First In, First Out queue
tc qdisc ... add pfifo [ limit packets ]
tc qdisc ... add bfifo [ limit bytes ]
The pfifo and bfifo qdiscs are unadorned First In, First Out
queues. They are the simplest queues possible and therefore have
no overhead. pfifo constrains the queue size as measured in
packets. bfifo does so as measured in bytes.
Like all non-default qdiscs, they maintain statistics. This might
be a reason to prefer pfifo or bfifo over the default.
A list of packets is maintained, when a packet is enqueued it gets
inserted at the tail of a list. When a packet needs to be sent out
to the network, it is taken from the head of the list.
If the list is too long, no further packets are allowed on. This
is called 'tail drop'.
limit Maximum queue size. Specified in bytes for bfifo, in
packets for pfifo. For pfifo, defaults to the interface
txqueuelen, as specified with ip(8). The range for this
parameter is [0, UINT32_MAX].
For bfifo, it defaults to the txqueuelen multiplied by the
interface MTU. The range for this parameter is [0,
UINT32_MAX] bytes.
Note: The link layer header was considered when counting
packets length.
The output of tc -s qdisc ls contains the limit, either in packets
or in bytes, and the number of bytes and packets actually sent. An
unsent and dropped packet only appears between braces and is not
counted as 'Sent'.
In this example, the queue length is 100 packets, 45894 bytes were
sent over 681 packets. No packets were dropped, and as the pfifo
queue does not slow down packets, there were also no overlimits:
# tc -s qdisc ls dev eth0
qdisc pfifo 8001: dev eth0 limit 100p
Sent 45894 bytes 681 pkts (dropped 0, overlimits 0)
If a backlog occurs, this is displayed as well.
tc(8)
Alexey N. Kuznetsov, <kuznet@ms2.inr.ac.ru>
This manpage maintained by bert hubert <ahu@ds9a.nl>
This page is part of the iproute2 (utilities for controlling
TCP/IP networking and traffic) project. Information about the
project can be found at
⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
If you have a bug report for this manual page, send it to
netdev@vger.kernel.org, shemminger@osdl.org. This page was
obtained from the project's upstream Git repository
⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-08-08.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to man-pages@man7.org
iproute2 10 January 2002 PBFIFO(8)
Pages that refer to this page: tc(8), tc-htb(8), tc-pfifo_fast(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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