| 1 | lttng-enable-channel(1) |
| 2 | ======================= |
| 3 | :revdate: 17 May 2021 |
| 4 | |
| 5 | |
| 6 | NAME |
| 7 | ---- |
| 8 | lttng-enable-channel - Create or enable LTTng channels |
| 9 | |
| 10 | |
| 11 | SYNOPSIS |
| 12 | -------- |
| 13 | Create a Linux kernel channel: |
| 14 | |
| 15 | [verse] |
| 16 | *lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *enable-channel* option:--kernel |
| 17 | [option:--discard | option:--overwrite] [option:--output=(**mmap** | **splice**)] |
| 18 | [option:--subbuf-size='SIZE'] [option:--num-subbuf='COUNT'] |
| 19 | [option:--switch-timer='PERIODUS'] [option:--read-timer='PERIODUS'] |
| 20 | [option:--monitor-timer='PERIODUS'] [option:--buffers-global] |
| 21 | [option:--tracefile-size='SIZE' [option:--tracefile-count='COUNT']] |
| 22 | [option:--session='SESSION'] 'CHANNEL' |
| 23 | |
| 24 | Create a user space channel: |
| 25 | |
| 26 | [verse] |
| 27 | *lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *enable-channel* option:--userspace |
| 28 | [option:--overwrite | [option:--discard] option:--blocking-timeout='TIMEOUTUS'] |
| 29 | [option:--output=**mmap**] [option:--buffers-uid | option:--buffers-pid] |
| 30 | [option:--subbuf-size='SIZE'] [option:--num-subbuf='COUNT'] |
| 31 | [option:--switch-timer='PERIODUS'] [option:--read-timer='PERIODUS'] |
| 32 | [option:--monitor-timer='PERIODUS'] |
| 33 | [option:--tracefile-size='SIZE' [option:--tracefile-count='COUNT']] |
| 34 | [option:--session='SESSION'] 'CHANNEL' |
| 35 | |
| 36 | Enable channel(s): |
| 37 | |
| 38 | [verse] |
| 39 | *lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *enable-channel* (option:--userspace | option:--kernel) |
| 40 | [option:--session='SESSION'] 'CHANNEL'[,'CHANNEL']... |
| 41 | |
| 42 | |
| 43 | DESCRIPTION |
| 44 | ----------- |
| 45 | The `lttng enable-channel` command does one of: |
| 46 | |
| 47 | * Create a channel named 'CHANNEL'. |
| 48 | |
| 49 | * Enable one or more disabled channels named 'CHANNEL' |
| 50 | (non-option argument, comma-separated). |
| 51 | |
| 52 | See man:lttng-concepts(7) to learn more about channels. |
| 53 | |
| 54 | The channel(s) to create or enable belong to: |
| 55 | |
| 56 | With the option:--session='SESSION' option:: |
| 57 | The tracing session named 'SESSION'. |
| 58 | |
| 59 | Without the option:--session option:: |
| 60 | The current tracing session (see man:lttng-concepts(7) to learn more |
| 61 | about the current tracing session). |
| 62 | |
| 63 | NOTE: The man:lttng-enable-event(1) command can automatically create a |
| 64 | default channel when no channel exists for the provided tracing domain. |
| 65 | |
| 66 | See the ``<<examples,EXAMPLES>>'' section below for usage examples. |
| 67 | |
| 68 | List the channels of a given tracing session with the |
| 69 | man:lttng-list(1) and man:lttng-status(1) commands. |
| 70 | |
| 71 | Disable an enabled channel with the man:lttng-disable-channel(1) |
| 72 | command. |
| 73 | |
| 74 | [IMPORTANT] |
| 75 | ==== |
| 76 | As of LTTng{nbsp}{lttng_version}, you may :not: perform the following |
| 77 | operations with the `enable-channel` command: |
| 78 | |
| 79 | * Change an attribute of an existing channel. |
| 80 | |
| 81 | * Enable a disabled channel once its tracing session has been active |
| 82 | (started; see man:lttng-start(1)) at least once. |
| 83 | |
| 84 | * Create a channel once its tracing session has been active at least |
| 85 | once. |
| 86 | |
| 87 | * Create a user space channel with a given buffering scheme |
| 88 | (option:--buffers-uid or option:--buffers-pid options) and create a |
| 89 | second user space channel with a different buffering scheme in the |
| 90 | same tracing session. |
| 91 | ==== |
| 92 | |
| 93 | |
| 94 | include::common-lttng-cmd-options-head.txt[] |
| 95 | |
| 96 | |
| 97 | Tracing domain |
| 98 | ~~~~~~~~~~~~~~ |
| 99 | One of: |
| 100 | |
| 101 | option:-k, option:--kernel:: |
| 102 | Create or enable channels in the Linux kernel domain. |
| 103 | |
| 104 | option:-u, option:--userspace:: |
| 105 | Create or enable channels in the user space domain. |
| 106 | |
| 107 | |
| 108 | Recording target |
| 109 | ~~~~~~~~~~~~~~~~ |
| 110 | option:-s 'SESSION', option:--session='SESSION':: |
| 111 | Create or enable channels in the tracing session named 'SESSION' |
| 112 | instead of the current tracing session. |
| 113 | |
| 114 | |
| 115 | Buffering scheme |
| 116 | ~~~~~~~~~~~~~~~~ |
| 117 | One of: |
| 118 | |
| 119 | option:--buffers-global:: |
| 120 | Allocate a single set of ring buffers for the whole system. |
| 121 | + |
| 122 | Only available with the option:--kernel option. |
| 123 | + |
| 124 | As of LTTng{nbsp}{lttng_version}, this is the default buffering scheme |
| 125 | for the Linux kernel tracing domain, but this may change in the future. |
| 126 | |
| 127 | option:--buffers-pid:: |
| 128 | Allocate one set of ring buffers (one per CPU) for each instrumented |
| 129 | process of: |
| 130 | + |
| 131 | -- |
| 132 | If you connect to the root session daemon:: |
| 133 | All Unix users. |
| 134 | + |
| 135 | See the ``Session daemon connection'' section of man:lttng(1) to learn |
| 136 | how a user application connects to a session daemon. |
| 137 | |
| 138 | Otherwise:: |
| 139 | Your Unix user. |
| 140 | -- |
| 141 | + |
| 142 | Only available with the option:--userspace option. |
| 143 | |
| 144 | option:--buffers-uid:: |
| 145 | Allocate one set of ring buffers (one per CPU) shared by all the |
| 146 | instrumented processes of: |
| 147 | + |
| 148 | -- |
| 149 | If you connect to the root session daemon:: |
| 150 | Each Unix user. |
| 151 | + |
| 152 | See the ``Session daemon connection'' section of man:lttng(1) to learn |
| 153 | how a user application connects to a session daemon. |
| 154 | |
| 155 | Otherwise:: |
| 156 | Your Unix user. |
| 157 | -- |
| 158 | + |
| 159 | Only available with the option:--userspace option. |
| 160 | + |
| 161 | As of LTTng{nbsp}{lttng_version}, this is the default buffering scheme |
| 162 | for the user space tracing domain, but this may change in the future. |
| 163 | |
| 164 | |
| 165 | Event record loss mode |
| 166 | ~~~~~~~~~~~~~~~~~~~~~~ |
| 167 | option:--blocking-timeout='TIMEOUTUS':: |
| 168 | Set the channel's blocking timeout value to __TIMEOUTUS__{nbsp}µs |
| 169 | for instrumented applications executed with a set |
| 170 | `LTTNG_UST_ALLOW_BLOCKING` environment variable. |
| 171 | + |
| 172 | 'TIMEOUTUS' is one of: |
| 173 | + |
| 174 | -- |
| 175 | `0` (default):: |
| 176 | Do not block (non-blocking mode). |
| 177 | |
| 178 | `inf`:: |
| 179 | Block forever until a sub-buffer is available to write the event |
| 180 | record. |
| 181 | |
| 182 | __N__, a positive value:: |
| 183 | Wait for at most __N__{nbsp}µs when trying to write to a sub-buffer. |
| 184 | After __N__{nbsp}µs, discard the event record. |
| 185 | -- |
| 186 | + |
| 187 | This option is only available with both the option:--userspace and |
| 188 | option:--discard options. |
| 189 | |
| 190 | One of: |
| 191 | |
| 192 | option:--discard:: |
| 193 | Discard event records when there's no available sub-buffer. |
| 194 | + |
| 195 | As of LTTng{nbsp}{lttng_version}, this is the default event record loss |
| 196 | mode, but this may change in the future. |
| 197 | |
| 198 | option:--overwrite:: |
| 199 | Overwrite the whole sub-buffer containing the oldest event records |
| 200 | when there's no available sub-buffer (flight recorder mode). |
| 201 | |
| 202 | |
| 203 | Sub-buffers |
| 204 | ~~~~~~~~~~~ |
| 205 | option:--num-subbuf='COUNT':: |
| 206 | Use 'COUNT' sub-buffers per ring buffer. |
| 207 | + |
| 208 | The effective value is 'COUNT' rounded up to the next power of two. |
| 209 | + |
| 210 | Default values: |
| 211 | + |
| 212 | option:--userspace and option:--buffers-uid options::: |
| 213 | +{default_ust_uid_channel_subbuf_num}+ |
| 214 | option:--userspace and option:--buffers-pid options::: |
| 215 | +{default_ust_pid_channel_subbuf_num}+ |
| 216 | option:--kernel and option:--buffers-global options::: |
| 217 | +{default_kernel_channel_subbuf_num}+ |
| 218 | `metadata` channel::: |
| 219 | +{default_metadata_subbuf_num}+ |
| 220 | |
| 221 | option:--output='TYPE':: |
| 222 | Set channel's output type to 'TYPE'. |
| 223 | + |
| 224 | 'TYPE' is one of: |
| 225 | + |
| 226 | -- |
| 227 | `mmap`::: |
| 228 | Share ring buffers between the tracer and the consumer daemon with |
| 229 | the man:mmap(2) system call. |
| 230 | |
| 231 | `splice`::: |
| 232 | Share ring buffers between the tracer and the consumer daemon |
| 233 | with the man:splice(2) system call. |
| 234 | + |
| 235 | Only available with the option:--kernel option. |
| 236 | -- |
| 237 | + |
| 238 | Default values: |
| 239 | + |
| 240 | option:--userspace and option:--buffers-uid options::: |
| 241 | `mmap` |
| 242 | option:--userspace and option:--buffers-pid options::: |
| 243 | `mmap` |
| 244 | option:--kernel and option:--buffers-global options::: |
| 245 | `splice` |
| 246 | `metadata` channel::: |
| 247 | `mmap` |
| 248 | |
| 249 | option:--subbuf-size='SIZE':: |
| 250 | Set the size of each sub-buffer to 'SIZE' bytes. |
| 251 | + |
| 252 | The effective value is 'SIZE' rounded up to the next power of two. |
| 253 | + |
| 254 | The `k`{nbsp}(KiB), `M`{nbsp}(MiB), and `G`{nbsp}(GiB) suffixes are |
| 255 | supported. |
| 256 | + |
| 257 | The minimum sub-buffer size, for each tracer, is the maximum value |
| 258 | between the default below and the system page size (see man:getconf(1) |
| 259 | with the `PAGE_SIZE` variable). |
| 260 | + |
| 261 | Default values: |
| 262 | + |
| 263 | option:--userspace and option:--buffers-uid options::: |
| 264 | +{default_ust_uid_channel_subbuf_size}+ |
| 265 | option:--userspace and option:--buffers-pid options::: |
| 266 | +{default_ust_pid_channel_subbuf_size}+ |
| 267 | option:--kernel and option:--buffers-global options::: |
| 268 | +{default_kernel_channel_subbuf_size}+ |
| 269 | `metadata` channel::: |
| 270 | +{default_metadata_subbuf_size}+ |
| 271 | |
| 272 | |
| 273 | Trace files |
| 274 | ~~~~~~~~~~~ |
| 275 | option:--tracefile-count='COUNT':: |
| 276 | Limit the number of trace files which LTTng writes for this channel |
| 277 | to 'COUNT'. |
| 278 | + |
| 279 | 'COUNT' set to `0` means ``unlimited''. |
| 280 | + |
| 281 | Default: +{default_channel_tracefile_count}+. |
| 282 | + |
| 283 | You must also use the option:--tracefile-size option with this option. |
| 284 | |
| 285 | option:--tracefile-size='SIZE':: |
| 286 | Set the maximum size of each trace file which LTTng writes for |
| 287 | this channel to __SIZE__{nbsp}bytes. |
| 288 | + |
| 289 | 'SIZE' set to `0` means ``unlimited''. |
| 290 | + |
| 291 | Default: +{default_channel_tracefile_size}+. |
| 292 | + |
| 293 | NOTE: Data streams which LTTng writes for a channel configured with this |
| 294 | option may inaccurately report discarded event records as of |
| 295 | CTF{nbsp}1.8. |
| 296 | |
| 297 | |
| 298 | Timers |
| 299 | ~~~~~~ |
| 300 | option:--monitor-timer='PERIODUS':: |
| 301 | Set the period of the monitor timer of the channel to |
| 302 | __PERIODUS__{nbsp}µs. |
| 303 | + |
| 304 | Set 'PERIODUS' to `0` to disable the monitor timer. |
| 305 | + |
| 306 | Default values: |
| 307 | + |
| 308 | option:--userspace and option:--buffers-uid options::: |
| 309 | +{default_ust_uid_channel_monitor_timer}+ |
| 310 | option:--userspace and option:--buffers-pid options::: |
| 311 | +{default_ust_pid_channel_monitor_timer}+ |
| 312 | option:--kernel and option:--buffers-global options::: |
| 313 | +{default_kernel_channel_monitor_timer}+ |
| 314 | |
| 315 | option:--read-timer='PERIODUS':: |
| 316 | Set the period of the read timer of the channel to |
| 317 | __PERIODUS__{nbsp}µs. |
| 318 | + |
| 319 | Set 'PERIODUS' to `0` to disable the read timer. |
| 320 | + |
| 321 | Default values: |
| 322 | + |
| 323 | option:--userspace and option:--buffers-uid options::: |
| 324 | +{default_ust_uid_channel_read_timer}+ |
| 325 | option:--userspace and option:--buffers-pid options::: |
| 326 | +{default_ust_pid_channel_read_timer}+ |
| 327 | option:--kernel and option:--buffers-global options::: |
| 328 | +{default_kernel_channel_read_timer}+ |
| 329 | `metadata` channel::: |
| 330 | +{default_metadata_read_timer}+ |
| 331 | |
| 332 | option:--switch-timer='PERIODUS':: |
| 333 | Set the period of the switch timer of the channel to |
| 334 | __PERIODUS__{nbsp}µs. |
| 335 | + |
| 336 | Set 'PERIODUS' to `0` to disable the switch timer. |
| 337 | + |
| 338 | Default values: |
| 339 | + |
| 340 | option:--userspace and option:--buffers-uid options::: |
| 341 | +{default_ust_uid_channel_switch_timer}+ |
| 342 | option:--userspace and option:--buffers-pid options::: |
| 343 | +{default_ust_pid_channel_switch_timer}+ |
| 344 | option:--kernel and option:--buffers-global options::: |
| 345 | +{default_kernel_channel_switch_timer}+ |
| 346 | `metadata` channel::: |
| 347 | +{default_metadata_switch_timer}+ |
| 348 | |
| 349 | |
| 350 | include::common-lttng-cmd-help-options.txt[] |
| 351 | |
| 352 | |
| 353 | include::common-lttng-cmd-after-options.txt[] |
| 354 | |
| 355 | |
| 356 | [[examples]] |
| 357 | EXAMPLES |
| 358 | -------- |
| 359 | .Create a Linux kernel channel with default attributes in the current tracing session. |
| 360 | ==== |
| 361 | The following command line only creates a new channel if `my-channel` |
| 362 | doesn't name an existing Linux kernel channel in the current tracing |
| 363 | session. |
| 364 | |
| 365 | [role="term"] |
| 366 | ---- |
| 367 | $ lttng enable-channel --kernel my-channel |
| 368 | ---- |
| 369 | ==== |
| 370 | |
| 371 | .Create a user space channel with a per-process buffering scheme in a specific tracing session. |
| 372 | ==== |
| 373 | See the option:--session and option:--buffers-pid options. |
| 374 | |
| 375 | [role="term"] |
| 376 | ---- |
| 377 | $ lttng enable-channel --session=my-session --userspace \ |
| 378 | --buffers-pid my-channel |
| 379 | ---- |
| 380 | ==== |
| 381 | |
| 382 | .Create a Linux kernel channel in the current tracing session with four 32-MiB sub-buffers per ring buffer. |
| 383 | ==== |
| 384 | See the option:--num-subbuf and option:--subbuf-size options. |
| 385 | |
| 386 | [role="term"] |
| 387 | ---- |
| 388 | $ lttng enable-channel --kernel my-channel \ |
| 389 | --num-subbuf=4 --subbuf-size=32M |
| 390 | ---- |
| 391 | ==== |
| 392 | |
| 393 | .Create a user space channel in the current tracing session with trace file rotation. |
| 394 | ==== |
| 395 | See the option:--tracefile-count and option:--tracefile-size options. |
| 396 | |
| 397 | [role="term"] |
| 398 | ---- |
| 399 | $ lttng enable-channel --userspace my-channel \ |
| 400 | --tracefile-count=16 --tracefile-size=8M |
| 401 | ---- |
| 402 | ==== |
| 403 | |
| 404 | .Enable two user space channels of a specific tracing session. |
| 405 | ==== |
| 406 | [role="term"] |
| 407 | ---- |
| 408 | $ lttng enable-channel --session=my-session --userspace \ |
| 409 | canal-d,rds |
| 410 | ---- |
| 411 | ==== |
| 412 | |
| 413 | |
| 414 | include::common-footer.txt[] |
| 415 | |
| 416 | |
| 417 | SEE ALSO |
| 418 | -------- |
| 419 | man:lttng(1), |
| 420 | man:lttng-disable-channel(1), |
| 421 | man:lttng-list(1), |
| 422 | man:lttng-concepts(7) |