[root@localhost thread]# ls
Makefile thread.c
[root@localhost thread]# gcc -o thread thread.c
/tmp/ccqJlBNV.o(.text+0xa6): In function `main':
: undefined reference to `pthread_create'
/tmp/ccqJlBNV.o(.text+0xde): In function `main':
: undefined reference to `pthread_create'
/tmp/ccqJlBNV.o(.text+0x111): In function `main':
: undefined reference to `pthread_join'
/tmp/ccqJlBNV.o(.text+0x121): In function `main':
: undefined reference to `pthread_join'
collect2: ld returned 1 exit status