- file streams (stdio) -
fclose
fgetc
fopen
fprintf
fputc
fread
fwrite
fscanf
fseek
getchar
printf
putchar
scanf
fstat

- strings -
strcasecmp
strcat
strcmp
strcpy
strlen

- file system calls -
close
open
read
write
lseek
unlink
stat

- process management -
execve
fork
getpid
getuid
wait

- threads -
pthread_create
pthread_exit
pthread_join
pthread_mutex_init
pthread_mutex_lock
pthread_mutex_unlock

- syncrhonization / shared memory -
sem_init
sem_post
sem_wait
shm_open
shm_unlink

- other -
free
malloc
memcpy
memset
realloc

sleep
time
usleep

random
srandom