Hi,

I am trying to use lttng library to trace user space.
I have installed the packages on Ubuntu as mentioned here :
http://lttng.org/download/#ubuntu
Also, I have download the git snapshot from
http://git.lttng.org/?p=lttng-ust.git;a=snapshot;h=HEAD;sf=tgz and
built the sources.

When I am trying to execute any of the application in example
directory I am not able to get the trace.
I have added myself to the tracing group using usermod and than did
the following:
ashish at ashish-pc:~/lttng/lttng-ust-HEAD-f4624de/doc/examples/demo-tracelog$ pwd
/home/ashish/lttng/lttng-ust-HEAD-f4624de/doc/examples/demo-tracelog
lttng create
lttng enable-event -u "lttng_ust_tracelog:*"
lttng start
./demo-tracelog
lttng stop

All the above commands were successfully completed. But when I am
trying to view the trace I am getting error.

ashish at ashish-pc:~/lttng/lttng-ust-HEAD-f4624de/doc/examples/demo-tracelog$
lttng view
Trace directory: /home/ashish/lttng-traces/auto-20160524-185123

[error] Cannot open any trace for reading.

[error] opening trace "/home/ashish/lttng-traces/auto-20160524-185123"
for reading.

[error] none of the specified trace paths could be opened.

ashish at ashish-pc:~/lttng/lttng-ust-HEAD-f4624de/doc/examples/demo-tracelog$
lttng destroy
Session auto-20160524-185123 destroyed

I will appreciate any help.

Regards,
Ashish

PS: BTW, installing lttng-modules-dkms failed for me (kernel version
3.19) with below error:
 DKMS make.log for lttng-modules-2.4.0 for kernel 3.19.0-31-generic (x86_64)
 Tue May 24 18:55:21 IST 2016
 make: Entering directory `/usr/src/linux-headers-3.19.0-31-generic'
   CC [M]  /var/lib/dkms/lttng-modules/2.4.0/build/lttng-ring-buffer-client-discard.o
 In file included from
/var/lib/dkms/lttng-modules/2.4.0/build/wrapper/ringbuffer/../../lib/ringbuffer/../../wrapper/ringbuffer/frontend_api.h:1:0,
                  from
/var/lib/dkms/lttng-modules/2.4.0/build/wrapper/ringbuffer/../../lib/ringbuffer/api.h:35,
                  from
/var/lib/dkms/lttng-modules/2.4.0/build/wrapper/ringbuffer/api.h:1,
                  from
/var/lib/dkms/lttng-modules/2.4.0/build/lttng-ring-buffer-client.h:175,
                  from
/var/lib/dkms/lttng-modules/2.4.0/build/lttng-ring-buffer-client-discard.c:29:
 /var/lib/dkms/lttng-modules/2.4.0/build/wrapper/ringbuffer/../../lib/ringbuffer/../../wrapper/ringbuffer/../../lib/ringbuffer/frontend_api.h:
In function ‘lib_ring_buffer_put_cpu’:
 /var/lib/dkms/lttng-modules/2.4.0/build/wrapper/ringbuffer/../../lib/ringbuffer/../../wrapper/ringbuffer/../../lib/ringbuffer/frontend_api.h:76:2:
error: implicit declaration of function ‘__get_cpu_var
 ’ [-Werror=implicit-function-declaration]
   __get_cpu_var(lib_ring_buffer_nesting)--;
   ^
 /var/lib/dkms/lttng-modules/2.4.0/build/wrapper/ringbuffer/../../lib/ringbuffer/../../wrapper/ringbuffer/../../lib/ringbuffer/frontend_api.h:76:40:
error: lvalue required as decrement operand
   __get_cpu_var(lib_ring_buffer_nesting)--;
                                         ^
 cc1: some warnings being treated as errors
 make[1]: *** [/var/lib/dkms/lttng-modules/2.4.0/build/lttng-ring-buffer-client-discard.o]
Error 1
 make: *** [_module_/var/lib/dkms/lttng-modules/2.4.0/build] Error 2
 make: Leaving directory `/usr/src/linux-headers-3.19.0-31-generic'