1.. SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
2
3================
4bpftool-link
5================
6-------------------------------------------------------------------------------
7tool for inspection and simple manipulation of eBPF links
8-------------------------------------------------------------------------------
9
10:Manual section: 8
11
12.. include:: substitutions.rst
13
14SYNOPSIS
15========
16
17	**bpftool** [*OPTIONS*] **link** *COMMAND*
18
19	*OPTIONS* := { |COMMON_OPTIONS| | { **-f** | **--bpffs** } | { **-n** | **--nomount** } }
20
21	*COMMANDS* := { **show** | **list** | **pin** | **help** }
22
23LINK COMMANDS
24=============
25
26|	**bpftool** **link { show | list }** [*LINK*]
27|	**bpftool** **link pin** *LINK* *FILE*
28|	**bpftool** **link detach** *LINK*
29|	**bpftool** **link help**
30|
31|	*LINK* := { **id** *LINK_ID* | **pinned** *FILE* }
32
33
34DESCRIPTION
35===========
36	**bpftool link { show | list }** [*LINK*]
37		  Show information about active links. If *LINK* is
38		  specified show information only about given link,
39		  otherwise list all links currently active on the system.
40
41		  Output will start with link ID followed by link type and
42		  zero or more named attributes, some of which depend on type
43		  of link.
44
45		  Since Linux 5.8 bpftool is able to discover information about
46		  processes that hold open file descriptors (FDs) against BPF
47		  links. On such kernels bpftool will automatically emit this
48		  information as well.
49
50	**bpftool link pin** *LINK* *FILE*
51		  Pin link *LINK* as *FILE*.
52
53		  Note: *FILE* must be located in *bpffs* mount. It must not
54		  contain a dot character ('.'), which is reserved for future
55		  extensions of *bpffs*.
56
57	**bpftool link detach** *LINK*
58		  Force-detach link *LINK*. BPF link and its underlying BPF
59		  program will stay valid, but they will be detached from the
60		  respective BPF hook and BPF link will transition into
61		  a defunct state until last open file descriptor for that
62		  link is closed.
63
64	**bpftool link help**
65		  Print short help message.
66
67OPTIONS
68=======
69	.. include:: common_options.rst
70
71	-f, --bpffs
72		  When showing BPF links, show file names of pinned
73		  links.
74
75	-n, --nomount
76		  Do not automatically attempt to mount any virtual file system
77		  (such as tracefs or BPF virtual file system) when necessary.
78
79EXAMPLES
80========
81**# bpftool link show**
82
83::
84
85    10: cgroup  prog 25
86            cgroup_id 614  attach_type egress
87            pids test_progs(223)
88
89**# bpftool --json --pretty link show**
90
91::
92
93    [{
94            "type": "cgroup",
95            "prog_id": 25,
96            "cgroup_id": 614,
97            "attach_type": "egress",
98            "pids": [{
99                    "pid": 223,
100                    "comm": "test_progs"
101                }
102            ]
103        }
104    ]
105
106|
107| **# bpftool link pin id 10 /sys/fs/bpf/link**
108| **# ls -l /sys/fs/bpf/**
109
110::
111
112    -rw------- 1 root root 0 Apr 23 21:39 link
113