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bpftool-link.rst

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bpftool-link

tool for inspection and simple manipulation of eBPF links

Manual section:8

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

-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