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1lttng-snapshot(1)
2=================
3
4
5NAME
6----
7lttng-snapshot - Take LTTng snapshots and configure snapshot outputs
8
9
10SYNOPSIS
11--------
12Add a snapshot output:
13
14[verse]
15*lttng* ['GENERAL OPTIONS'] *snapshot add-output* [option:--max-size='SIZE']
16 [option:--name='NAME'] [option:--session='SESSION']
17 (option:--ctrl-url='URL' option:--data-url='URL' | 'URL')
18
19Remove a snapshot output:
20
21[verse]
22*lttng* ['GENERAL OPTIONS'] *snapshot del-output* [option:--session='SESSION']
23 ('ID' | 'NAME')
24
25List current snapshot outputs:
26
27[verse]
28*lttng* ['GENERAL OPTIONS'] *snapshot list-output* [option:--session='SESSION']
29
30Take a snapshot:
31
32[verse]
33*lttng* ['GENERAL OPTIONS'] *snapshot record* [option:--max-size='SIZE']
34 [option:--name='NAME'] [option:--session='SESSION']
35 (option:--ctrl-url='URL' option:--data-url='URL' | 'URL')
36
37
38DESCRIPTION
39-----------
40The `lttng snapshot` command manages the snapshot outputs and takes
41snapshots.
42
43A _snapshot_ is a dump of the current sub-buffers of all the channels
44of a given tracing session. When a snapshot is taken, the memory dump
45is sent to the registered snapshot outputs.
46
47The tracing session should be created in _snapshot mode_ to make sure
48taking snapshots is allowed. This is done at tracing session creation
49time using the linklttng:lttng-create(1) command.
50
51Note that, when a snapshot is taken, the sub-buffers are not cleared.
52This means that different recorded snapshots may contain the same
53events.
54
55
56Snapshot outputs
57~~~~~~~~~~~~~~~~
58Snapshot outputs are the destinations of snapshot files when a
59snapshot is taken using the `record` action.
60
61As of this version, only one snapshot output is allowed.
62
63A snapshot output can be added using the `add-output` action. The
64output destination URL is set using either the 'URL' positional
65argument, or both the option:--ctrl-url and option:--data-url options.
66See linklttng:lttng-create(1) to learn more about the URL format.
67
68A name can be assigned to an output when adding it using the
69option:--name option. This name is part of the names of the
70snapshot files written to this output.
71
72By default, the snapshot files can be as big as the sum of the
73sizes of all the sub-buffers or all the channels of the selected
74tracing session. The maximum total size of all the snapshot files can
75be configured using the option:--max-size option.
76
77Snapshot outputs can be listed using the `list-output` action.
78
79Snapshot outputs can be removed using the `del-output` action. The
80configured name can be used when removing an output, or an ID as
81listed by the `list-output` action.
82
83
84Taking a snapshot
85~~~~~~~~~~~~~~~~~
86Taking a snapshot of the current tracing session is as easy as:
87
88---------------------
89lttng snapshot record
90---------------------
91
92This writes the snapshot files to the configured output. It is possible
93to use a custom, unregistered output at record time using the same
94options supported by the `add-output` action.
95
96NOTE: Before taking a snapshot on a system with a high event throughput,
97it is recommended to first run `lttng stop` (see
98linklttng:lttng-stop(1)). Otherwise, the snapshot could contain "holes",
99the result of the tracers overwriting unconsumed trace packets during
100the record operation. After the snapshot is recorded, the tracers can be
101started again with `lttng start` (see linklttng:lttng-start(1)).
102
103
104include::common-cmd-options-head.txt[]
105
106
107Target
108~~~~~~
109option:-s, option:--session='SESSION'::
110 Take a snapshot of the sub-buffers of the channels contained in
111 the tracing session named 'SESSION' instead of the current
112 tracing session.
113
114
115Snapshot output
116~~~~~~~~~~~~~~~
117option:-C, option:--ctrl-url='URL'::
118 Set control path URL to 'URL' (must use option:--data-url option
119 also).
120
121option:-D, option:--data-url='URL'::
122 Set data path URL to 'URL' (must use option:--ctrl-url option
123 also).
124
125option:-m, option:--max-size='SIZE'::
126 Limit the total size of all the snapshot files written when
127 recording a snapshot to 'SIZE' bytes. The `k` (kiB), `M` (MiB),
128 and `G` (GiB) suffixes are supported.
129
130option:-n, option:--name='NAME'::
131 Assign the name 'NAME' to the snapshot output.
132
133
134include::common-cmd-help-options.txt[]
135
136
137include::common-cmd-footer.txt[]
138
139
140SEE ALSO
141--------
142linklttng:lttng-untrack(1),
143linklttng:lttng(1)
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