General options are described in lttng(1).
Domain
One of:
-k, --kernel
Enable channel in the Linux kernel domain.
-u, --userspace
Enable channel in the user space domain.
Target
-s SESSION, --session=SESSION
Create or enable channel in the tracing session named SESSION
instead of the current tracing session.
Event loss mode
--blocking-timeout=TIMEOUTUS
Set the channel's blocking timeout value to TIMEOUTUS µs for
instrumented applications executed with a set
LTTNG_UST_ALLOW_BLOCKING environment variable:
0 (default)
Do not block (non-blocking mode).
inf
Block forever until room is available in the sub-buffer
to write the event record.
n, a positive value
Wait for at most n µs when trying to write into a
sub-buffer. After n µs, discard the event record.
This option is only available with the --userspace option and
without the --overwrite option.
One of:
--discard
Discard events when sub-buffers are full (default).
--overwrite
Flight recorder mode: always keep a fixed amount of the
latest data.
Sub-buffers
--num-subbuf=COUNT
Use COUNT sub-buffers. Rounded up to the next power of two.
Default values:
• --userspace and --buffers-uid options: 4
• --userspace and --buffers-pid options: 4
• --kernel option: 4
• metadata channel: 2
--output=TYPE
Set channel's output type to TYPE.
Available types: mmap (always available) and splice (only
available with the --kernel option).
Default values:
• --userspace and --buffers-uid options: mmap
• --userspace and --buffers-pid options: mmap
• --kernel option: splice
• metadata channel: mmap
--subbuf-size=SIZE
Set the individual size of sub-buffers to SIZE bytes. The k
(kiB), M (MiB), and G (GiB) suffixes are supported. Rounded
up to the next power of two.
The minimum sub-buffer size, for each tracer, is the maximum
value between the default below and the system's page size.
The following command shows the current system's page size:
getconf PAGE_SIZE.
Default values:
• --userspace and --buffers-uid options: 524288
• --userspace and --buffers-pid options: 16384
• --kernel option: 1048576
• metadata channel: 4096
Buffering scheme
One of:
--buffers-global
Use shared sub-buffers for the whole system (only available
with the --kernel option).
--buffers-pid
Use different sub-buffers for each traced process (only
available with the the --userspace option). This is the
default buffering scheme for user space channels.
--buffers-uid
Use shared sub-buffers for all the processes of the user
running the command (only available with the --userspace
option).
Trace files
--tracefile-count=COUNT
Limit the number of trace files created by this channel to
COUNT. 0 means unlimited. Default: 0.
Use this option in conjunction with the --tracefile-size
option.
The file count within a stream is appended to each created
trace file. If COUNT files are created and more events need
to be recorded, the first trace file of the stream is cleared
and used again.
--tracefile-size=SIZE
Set the maximum size of each trace file written by this
channel within a stream to SIZE bytes. 0 means unlimited.
Default: 0.
Note: traces generated with this option may inaccurately
report discarded events as of CTF 1.8.
Timers
--monitor-timer
Set the channel's monitor timer's period to PERIODUS µs. 0
means a disabled monitor timer.
Default values:
• --userspace and --buffers-uid options: 1000000
• --userspace and --buffers-pid options: 1000000
• --kernel option: 1000000
--read-timer
Set the channel's read timer's period to PERIODUS µs. 0 means
a disabled read timer.
Default values:
• --userspace and --buffers-uid options: 0
• --userspace and --buffers-pid options: 0
• --kernel option: 200000
• metadata channel: 0
--switch-timer=PERIODUS
Set the channel's switch timer's period to PERIODUS µs. 0
means a disabled switch timer.
Default values:
• --userspace and --buffers-uid options: 0
• --userspace and --buffers-pid options: 0
• --kernel option: 0
• metadata channel: 0
Program information
-h, --help
Show command help.
This option, like lttng-help(1), attempts to launch
/usr/bin/man to view the command's man page. The path to the
man pager can be overridden by the LTTNG_MAN_BIN_PATH
environment variable.
--list-options
List available command options.
