.. 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