xref: /linux/tools/bpf/bpftool/Documentation/bpftool-link.rst (revision ea379b3c)

.. SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)

================
bpftool-link
================
-------------------------------------------------------------------------------
tool for inspection and simple manipulation of eBPF links
-------------------------------------------------------------------------------

:Manual section: 8

.. include:: substitutions.rst

SYNOPSIS
========

**bpftool** [*OPTIONS*] **link** *COMMAND*

*OPTIONS* := { |COMMON_OPTIONS| | { **-f** | **--bpffs** } | { **-n** | **--nomount** } }

*COMMANDS* := { **show** | **list** | **pin** | **help** }

LINK COMMANDS
=============

| **bpftool** **link { show | list }** [*LINK*]
| **bpftool** **link pin** *LINK* *FILE*
| **bpftool** **link detach** *LINK*
| **bpftool** **link help**
|
| *LINK* := { **id** *LINK_ID* | **pinned** *FILE* }


DESCRIPTION
===========
bpftool link { show | list } [*LINK*]
    Show information about active links. If *LINK* is specified show
    information only about given link, otherwise list all links currently
    active on the system.

    Output will start with link ID followed by link type and zero or more named
    attributes, some of which depend on type of link.

    Since Linux 5.8 bpftool is able to discover information about processes
    that hold open file descriptors (FDs) against BPF links. On such kernels
    bpftool will automatically emit this information as well.

bpftool link pin *LINK* *FILE*
    Pin link *LINK* as *FILE*.

    Note: *FILE* must be located in *bpffs* mount. It must not contain a dot
    character ('.'), which is reserved for future extensions of *bpffs*.

bpftool link detach *LINK*
    Force-detach link *LINK*. BPF link and its underlying BPF program will stay
    valid, but they will be detached from the respective BPF hook and BPF link
    will transition into a defunct state until last open file descriptor for
    that link is closed.

bpftool link help
    Print short help message.

OPTIONS
=======
    .. include:: common_options.rst

    -f, --bpffs
        When showing BPF links, show file names of pinned links.

    -n, --nomount
        Do not automatically attempt to mount any virtual file system (such as
        tracefs or BPF virtual file system) when necessary.

EXAMPLES
========
**# bpftool link show**

::

    10: cgroup  prog 25
            cgroup_id 614  attach_type egress
            pids test_progs(223)

**# bpftool --json --pretty link show**

::

    [{
            "type": "cgroup",
            "prog_id": 25,
            "cgroup_id": 614,
            "attach_type": "egress",
            "pids": [{
                    "pid": 223,
                    "comm": "test_progs"
                }
            ]
        }
    ]

|
| **# bpftool link pin id 10 /sys/fs/bpf/link**
| **# ls -l /sys/fs/bpf/**

::

    -rw------- 1 root root 0 Apr 23 21:39 link