trace-cmd-show - Man Page

show the contents of the Ftrace Linux kernel tracing buffer.

Description

The trace-cmd(1) show displays the contents of one of the Ftrace Linux kernel tracing files: trace, snapshot, or trace_pipe. It is basically the equivalent of doing:

cat /sys/kernel/debug/tracing/trace

Instead of displaying the contents of the "trace" file, use the "trace_pipe" file. The difference between the two is that the "trace" file is static. That is, if tracing is stopped, the "trace" file will show the same contents each time.

The "trace_pipe" file is a consuming read, where a read of the file
will consume the output of what was read and it will not read the
same thing a second time even if tracing is stopped. This file
als will block. If no data is available, trace-cmd show will stop
and wait for data to appear.

-s

Instead of reading the "trace" file, read the snapshot file. The snapshot is made by an application writing into it and the kernel will perform as swap between the currently active buffer and the current snapshot buffer. If no more swaps are made, the snapshot will remain static. This is not a consuming read.

-c cpu

Read only the trace file for a specified CPU.

-f

Display the full path name of the file that is being displayed.

-B buf

If a buffer instance was created, then the -B option will access the files associated with the given buffer.

--tracing_on

Show if tracing is on for the given instance.

--current_tracer

Show what the current tracer is.

--buffer_size

Show the current buffer size (per-cpu)

--buffer_total_size

Show the total size of all buffers.

--buffer_subbuf_size

Show the size in kilobytes of the sub-buffers of the ring buffer. The ring buffer is broken up into equal size sub-buffers were an event can only be as big as the sub-buffer data section (the size minus its meta data).

--buffer_percent

Show the percentage the buffer must be filled before a reader that is blocked on the trace_pipe_raw file will be woken up.

0       : wake up immediately on any new data
1 - 99  : wake up on this percentage of the sub-buffers being full
100     : wake up after the buffer is full and the writer is on the last sub-buffer

--ftrace_filter