Hands-On System Programming with Linux

The actual system call

We have seen several APIs that perform the work of having the parent process wait until the child changes state (dies, or stops, or resumes after stop):

• wait
• waitpid
• waitid
• wait3
• wait4

Interestingly, and similar to the situation with the exec family APIs, the Linux implementation is such that most of the preceding APIs are library (glibc) wrappers: The fact is that, on the Linux OS, of all the preceding APIs, wait4(2) is the actual system call API.

Performing an strace(1) on a program that uses one of the wait APIs proves the point (we strace our simpsh_v1 program, which calls wait):

$ strace -e trace=process -o strc.txt ./simpsh_v1 >> ps PID TTY TIME CMD14874 pts/6 00:00:00 bash27248 pts/6 00:00:00 strace27250 pts/6 ...