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BPFTOOL-LINK(8) System Manager's Manual BPFTOOL-LINK(8)

NAME

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

SYNOPSIS

bpftool [OPTIONS] link COMMAND

OPTIONS := { { -j | --json } [{ -p | --pretty }] | { -d | --debug } | { -l | --legacy } | { -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

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.

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.

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.
Print short help message.



OPTIONS

Print short help message (similar to bpftool help).
Print bpftool's version number (similar to bpftool version), the number of the libbpf version in use, and optional features that were included when bpftool was compiled. Optional features include linking against libbfd to provide the disassembler for JIT-ted programs (bpftool prog dump jited) and usage of BPF skeletons (some features like bpftool prog profile or showing pids associated to BPF objects may rely on it).
Generate JSON output. For commands that cannot produce JSON, this option has no effect.
Generate human-readable JSON output. Implies -j.
Print all logs available, even debug-level information. This includes logs from libbpf as well as from the verifier, when attempting to load programs.
Use legacy libbpf mode which has more relaxed BPF program requirements. By default, bpftool has more strict requirements about section names, changes pinning logic and doesn't support some of the older non-BTF map declarations.

See https://github.com/libbpf/libbpf/wiki/Libbpf:-the-road-to-v1.0 for details.


When showing BPF links, show file names of pinned links.
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


SEE ALSO

bpf(2), bpf-helpers(7), bpftool(8), bpftool-btf(8), bpftool-cgroup(8), bpftool-feature(8), bpftool-gen(8), bpftool-iter(8), bpftool-map(8), bpftool-net(8), bpftool-perf(8), bpftool-prog(8), bpftool-struct_ops(8)