pid_t getsid(pid_t pid);
描述getsid(0) 返回调用进程的会话ID. getsid(p) 返回与进程ID的进程的会话ID p. (一个进程的会话ID是会话组长的进程组ID.) On error, (pid_t) -1 will be returned, and errno is set appropriately.
|EPERM||A process with process ID p exists, but it is not in the same session as the current process, and the implementation considers this an error.|
|ESRCH||No process with process ID p was found.|
注意Linux does not return EPERM.
Linux has this system call since Linux 1.3.44. There is libc support since libc 5.2.19.
To get the prototype under glibc, define both _XOPEN_SOURCE and _XOPEN_SOURCE_EXTENDED, or use "#define _XOPEN_SOURCE n" for some integer nlarger than or equal to 500.