{ "mode": "man", "parameter": "tc-prio", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/tc-prio/8/json", "generated": "2026-06-02T21:27:36Z", "synopsis": "tc qdisc ... dev dev ( parent classid | root) [ handle major: ] prio [ bands bands ] [ pri‐‐\nomap band band band... ] [ estimator interval timeconstant ]", "sections": { "NAME": { "content": "PRIO - Priority qdisc\n", "subsections": [] }, "SYNOPSIS": { "content": "tc qdisc ... dev dev ( parent classid | root) [ handle major: ] prio [ bands bands ] [ pri‐‐\nomap band band band... ] [ estimator interval timeconstant ]\n\n", "subsections": [] }, "DESCRIPTION": { "content": "The PRIO qdisc is a simple classful queueing discipline that contains an arbitrary number of\nclasses of differing priority. The classes are dequeued in numerical descending order of pri‐\nority. PRIO is a scheduler and never delays packets - it is a work-conserving qdisc, though\nthe qdiscs contained in the classes may not be.\n\nVery useful for lowering latency when there is no need for slowing down traffic.\n\n", "subsections": [] }, "ALGORITHM": { "content": "On creation with 'tc qdisc add', a fixed number of bands is created. Each band is a class,\nalthough is not possible to add classes with 'tc qdisc add', the number of bands to be cre‐\nated must instead be specified on the command line attaching PRIO to its root.\n\nWhen dequeueing, band 0 is tried first and only if it did not deliver a packet does PRIO try\nband 1, and so onwards. Maximum reliability packets should therefore go to band 0, minimum\ndelay to band 1 and the rest to band 2.\n\nAs the PRIO qdisc itself will have minor number 0, band 0 is actually major:1, band 1 is ma‐\njor:2, etc. For major, substitute the major number assigned to the qdisc on 'tc qdisc add'\nwith the handle parameter.\n\n", "subsections": [] }, "CLASSIFICATION": { "content": "Three methods are available to PRIO to determine in which band a packet will be enqueued.\n\nFrom userspace\nA process with sufficient privileges can encode the destination class directly with\nSOPRIORITY, see socket(7).\n\nwith a tc filter\nA tc filter attached to the root qdisc can point traffic directly to a class\n\nwith the priomap\nBased on the packet priority, which in turn is derived from the Type of Service as‐\nsigned to the packet.\n\nOnly the priomap is specific to this qdisc.\n", "subsections": [] }, "QDISC PARAMETERS": { "content": "bands Number of bands. If changed from the default of 3, priomap must be updated as well.\n\npriomap\nThe priomap maps the priority of a packet to a class. The priority can either be set\ndirectly from userspace, or be derived from the Type of Service of the packet.\n\nDetermines how packet priorities, as assigned by the kernel, map to bands. Mapping oc‐\ncurs based on the TOS octet of the packet, which looks like this:\n\n0 1 2 3 4 5 6 7\n+---+---+---+---+---+---+---+---+\n| | | |\n|PRECEDENCE | TOS |MBZ|\n| | | |\n+---+---+---+---+---+---+---+---+\n\nThe four TOS bits (the 'TOS field') are defined as:\n\nBinary Decimal Meaning\n-----------------------------------------\n1000 8 Minimize delay (md)\n0100 4 Maximize throughput (mt)\n0010 2 Maximize reliability (mr)\n0001 1 Minimize monetary cost (mmc)\n0000 0 Normal Service\n\nAs there is 1 bit to the right of these four bits, the actual value of the TOS field\nis double the value of the TOS bits. Tcpdump -v -v shows you the value of the entire\nTOS field, not just the four bits. It is the value you see in the first column of this\ntable:\n\nTOS Bits Means Linux Priority Band\n------------------------------------------------------------\n0x0 0 Normal Service 0 Best Effort 1\n0x2 1 Minimize Monetary Cost 0 Best Effort 1\n0x4 2 Maximize Reliability 0 Best Effort 1\n0x6 3 mmc+mr 0 Best Effort 1\n0x8 4 Maximize Throughput 2 Bulk 2\n0xa 5 mmc+mt 2 Bulk 2\n0xc 6 mr+mt 2 Bulk 2\n0xe 7 mmc+mr+mt 2 Bulk 2\n0x10 8 Minimize Delay 6 Interactive 0\n0x12 9 mmc+md 6 Interactive 0\n0x14 10 mr+md 6 Interactive 0\n0x16 11 mmc+mr+md 6 Interactive 0\n0x18 12 mt+md 4 Int. Bulk 1\n0x1a 13 mmc+mt+md 4 Int. Bulk 1\n0x1c 14 mr+mt+md 4 Int. Bulk 1\n0x1e 15 mmc+mr+mt+md 4 Int. Bulk 1\n\nThe second column contains the value of the relevant four TOS bits, followed by their\ntranslated meaning. For example, 15 stands for a packet wanting Minimal Monetary Cost,\nMaximum Reliability, Maximum Throughput AND Minimum Delay.\n\nThe fourth column lists the way the Linux kernel interprets the TOS bits, by showing\nto which Priority they are mapped.\n\nThe last column shows the result of the default priomap. On the command line, the de‐\nfault priomap looks like this:\n\n1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1\n\nThis means that priority 4, for example, gets mapped to band number 1. The priomap\nalso allows you to list higher priorities (> 7) which do not correspond to TOS map‐\npings, but which are set by other means.\n\nThis table from RFC 1349 (read it for more details) explains how applications might\nvery well set their TOS bits:\n\nTELNET 1000 (minimize delay)\nFTP\nControl 1000 (minimize delay)\nData 0100 (maximize throughput)\n\nTFTP 1000 (minimize delay)\n\nSMTP\nCommand phase 1000 (minimize delay)\nDATA phase 0100 (maximize throughput)\n\nDomain Name Service\nUDP Query 1000 (minimize delay)\nTCP Query 0000\nZone Transfer 0100 (maximize throughput)\n\nNNTP 0001 (minimize monetary cost)\n\nICMP\nErrors 0000\nRequests 0000 (mostly)\nResponses (mostly)\n\n\n", "subsections": [] }, "CLASSES": { "content": "PRIO classes cannot be configured further - they are automatically created when the PRIO\nqdisc is attached. Each class however can contain yet a further qdisc.\n\n", "subsections": [] }, "BUGS": { "content": "Large amounts of traffic in the lower bands can cause starvation of higher bands. Can be pre‐\nvented by attaching a shaper (for example, tc-tbf(8) to these bands to make sure they cannot\ndominate the link.\n\n", "subsections": [] }, "AUTHORS": { "content": "Alexey N. Kuznetsov, , J Hadi Salim . This manpage\nmaintained by bert hubert \n\n\n\niproute2 16 December 2001 PRIO(8)", "subsections": [] } }, "summary": "PRIO - Priority qdisc", "flags": [], "examples": [], "see_also": [] }