bpftool-link - tool for inspection and simple manipulation of eBPF
links
bpftool [
OPTIONS]
link
COMMAND
OPTIONS := { { -j | --json } [{ -p |
--pretty }] | { -d | --debug } | { -l |
--legacy } | { -f | --bpffs } | { -n |
--nomount } }
COMMANDS := { show | list | pin |
help }
bpftool link { show | list } [LINK]
bpftool link pin LINK FILE
bpftool link detach LINK
bpftool link help
LINK := { id LINK_ID | pinned FILE }
- 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.
- -h,
--help
- Print short help message (similar to bpftool help).
- -V,
--version
- 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).
- -j,
--json
- Generate JSON output. For commands that cannot produce JSON, this option
has no effect.
- -p,
--pretty
- Generate human-readable JSON output. Implies -j.
- -d,
--debug
- Print all logs available, even debug-level information. This includes logs
from libbpf as well as from the verifier, when attempting to load
programs.
- -l,
--legacy
- 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.
- -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.
# bpftool link show
# 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
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)