posix: Get parent process id and name

get_ppid_and_name.c

#ifdef SHELL
gcc -Wall -Werror $0 && ./a.out
exit $?
#endif

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>

/**
 * Get a process name from its PID.
 * @param pid PID of the process
 * @param name Name of the process
 * 
 * Source: http://stackoverflow.com/questions/15545341/process-name-from-its-pid-in-linux
 */
static void get_process_name(const pid_t pid, char * name) {
	char procfile[BUFSIZ];
	sprintf(procfile, "/proc/%d/cmdline", pid);
	FILE* f = fopen(procfile, "r");
	if (f) {
		size_t size;
		size = fread(name, sizeof (char), sizeof (procfile), f);
		if (size > 0) {
			if ('\n' == name[size - 1])
				name[size - 1] = '\0';
		}
		fclose(f);
	}
}

/**
 * Get the parent PID from a PID
 * @param pid pid
 * @param ppid parent process id
 * 
 * Note: init is 1 and it has a parent id of 0.
 */
static void get_process_parent_id(const pid_t pid, pid_t * ppid) {
	char buffer[BUFSIZ];
	sprintf(buffer, "/proc/%d/stat", pid);
	FILE* fp = fopen(buffer, "r");
	if (fp) {
		size_t size = fread(buffer, sizeof (char), sizeof (buffer), fp);
		if (size > 0) {
			// See: http://man7.org/linux/man-pages/man5/proc.5.html section /proc/[pid]/stat
			strtok(buffer, " "); // (1) pid  %d
			strtok(NULL, " "); // (2) comm  %s
			strtok(NULL, " "); // (3) state  %c
			char * s_ppid = strtok(NULL, " "); // (4) ppid  %d
			*ppid = atoi(s_ppid);
		}
		fclose(fp);
	}
}

int main(int argc, char *argv[]) {
	pid_t pid = getpid();
	while (pid != 0) {
		char name[BUFSIZ];
		get_process_name(pid, name);
		printf("%6d - %s\n", pid, name);
		get_process_parent_id(pid, & pid);
	}
	return 0;
}

/* Your should get something like that:
 24090 - ./a.out
 24084 - bash
  2425 - bash
  1369 - /usr/bin/xfce4-terminal
 13056 - init
 12994 - lightdm
  1428 - lightdm
     1 - /sbin/initsession-child
*/

And if you don't have /proc filesystem? This is a rhetorical question, of course :)

change posix to unix. not every posix system has /proc

@fclairamb Could you please state under which license you put this code?

I would like to use it in a GPL2 licensed project and want to follow the rules ;-)

Edit: Intended usage would be this -> mcdope/pam_usb#45

@mcdope License would be MIT

Thanks for clarifying!

simple and cool code! love it.

For C++ guys, here is the version you look for:

const auto parentProcessName = []() -> std::string {
    const std::string cmdlinePath = "/proc/" + std::to_string(::getppid()) + "/cmdline";

    std::ifstream file(cmdlinePath);
    if (!file.is_open()) {
        PLOGE << "Failed to open parent process name file: " << cmdlinePath;

        return "";
    }

    std::string parentProcessName;
    std::getline(file, parentProcessName);

    return parentProcessName;
}();