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