How to use pthread functions on Colibri iMX6ULL

Hi. I’m using iMX6ULL 512MB WB IT and I want to use pthread functions for multi-tasking. I followed one example code in Toradex community but there is a compile error. Please let me know how to build pthread functions.

My compiler Settings are the followings.


. /usr/local/oecore-x86_64/environment-setup-armv7at2hf-neon-angstrom-linux-gnueabi

C/C++ Build/Settings

  - Cross GCC compiler : ${CC}
       Miscellaneous : ${CFLAGS} -c
  - Cross GCC Linker : ${CXX}
       Miscellaneous : ${LDFLAGS}

The following is my code.

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h> 
#include <termios.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <pthread.h>

void *print_message_function( void *ptr );
void test(void);

int main(int argc, char *argv[])

void test(void)
pthread_t thread1, thread2;
char *message1 = "Thread 1";
char *message2 = "Thread 2";
int  iret1, iret2;

/* Create independent threads each of which will execute function */
iret1 = pthread_create( &thread1, NULL, print_message_function, (void*) message1);
iret2 = pthread_create( &thread2, NULL, print_message_function, (void*) message2);

/* Wait till threads are complete before main continues. Unless we  */
/* wait we run the risk of executing an exit which will terminate   */
/* the process and all threads before the threads have completed.   */
pthread_join( thread1, NULL);
pthread_join( thread2, NULL);

printf("Thread 1 returns: %d\n",iret1);
printf("Thread 2 returns: %d\n",iret2);

void *print_message_function( void *ptr )
     char *message;
     message = (char *) ptr;
     printf("%s \n", message);

Invoking: Cross GCC Linker

arm-angstrom-linux-gnueabi-g++ -march=armv7-a -mthumb -mfpu=neon -mfloat-abi=hard --sysroot=/usr/local/oecore-x86_64/sysroots/armv7at2hf-neon-angstrom-linux-gnueabi -Wl,-O1 -Wl,–hash-style=gnu -Wl,–as-needed -o “hello-world” ./src/hello-world.o

…/src/hello-world.c:117: error: undefined reference to ‘pthread_create’

makefile:30: recipe for target ‘hello-world’ failed

…/src/hello-world.c:118: error: undefined reference to ‘pthread_create’

…/src/hello-world.c:124: error: undefined reference to ‘pthread_join’

…/src/hello-world.c:125: error: undefined reference to ‘pthread_join’

collect2: error: ld returned 1 exit status

make: *** [hello-world] Error 1

Hi @HansKim72

Thanks for writing to the Toradex Community!

./src/hello-world.c:117: error: undefined reference to ‘pthread_create’

Did you add pthread to your linker libraries as explained in this thread?

Best regards,


If your program needs code from a library you have to tell the linker the name of the library to link against. Usually that is done with the “-l” option.

pthread is special as there is a special option “-pthread” which should be given to both compiler and linker.

So you have to add -pthread to CFLAGS and LDFLAGS.


Thank you. Settled.

Perfect that it works. Thanks for the feedback.

If you’re building in eclipse neon to build and configure imx6ull. Go to properties - c/c++ build - settings - crossGccCompiler - miscellaneous. Then make sure you have pthread added in both CFLAGS and LDFLAGS.
It should look like this.

${CFLAGS} -c -pthread //for CFLAGS
${LDFLAGS} -pthread //for LDFLAGS

As stated in the answer pthread must be added to both the compiler and the linker respectively.

Hi @BenjFTL

Welcome to the Toradex Community!
Thanks for your valuable Input.

Best regards,