This is a common error while compiling C program in Linux. This error occurs when you are using pthread_create function to create threads in your programs.
To fix this problem ensure following points: Include header file pthread.h in your program. Add –lpthread linker flag with compilation command. 1- Include Header file #include <stdio.h> #include <pthread.h> ... ... 2- Compile command gcc main.c -o main -lpthread