C - printing linux process table

[seranmca]

Hello,
I need to write a C program, which can print all the processes currently running with their process ids. I dont know where to start. Is there any system call available to get the list of processes and its ids? Can any one give me some ideas, so that I can proceed from there.

Thanks
Seran

[bigtomrodney]

ps aux

will give you details of system processes.

top

runs an interactive CLI tool for monitoring, if you can extract anything there either.

[seranmca]

I should use not system() - system call in my C program. I have to read all the entries in the linux process table and I have to print process names with its ids.

This will be a pure C programming work, without using shell commands.

[Santa's little helper]

The /proc directory has that info.I believe it has a listing of
the ids of all processes.

[seranmca]

Thanks. got it.

I have to search thru the numbered directories (process ids) and those exe links (process names) .

[Dolda2000]

You may want to consider using libproc, which is the library used by ps, top and related programs. I don't know where to get hold of the documentation for it, though.

[Fallen Angel]

Yes, I also heard that libproc is good for these things, cause I'm thinking on doing something similar too.

[seranmca]

I had written a small program to return the process-id of a process. I thought this will be usefull, and the code is here....

#include <dirent.h>
#include <stdio.h>
#include <stdlib.h>

unsigned int getProcessID&#40; char *process &#41;
&#123;
  int target_link;
  DIR *dir_p;
  DIR *dir_proc;
  struct dirent *dir_entry_p;
  struct dirent *dir_proc_p;
  char dir_name&#91;35&#93;;
  char target_name&#91;235&#93;;
  char exe_link&#91;235&#93;;
  char process_id&#91;20&#93;;
  int i;

  dir_p = opendir&#40; "/proc/" &#41;; /* Open /proc/ directory */

  while&#40; NULL != &#40;dir_entry_p = readdir&#40;dir_p&#41;&#41;&#41; /* Reading /proc/ entries */
    &#123;
      if &#40; strspn&#40; dir_entry_p->d_name, "0123456789" &#41; == strlen&#40; dir_entry_p->d_name &#41; &#41; /* Checking for numbered directories */
	&#123;
	  strcpy&#40; process_id, dir_entry_p->d_name &#41;; /* Saving the numbered directory i.e process-id */

	  strcpy&#40; dir_name, "/proc/" &#41;;
	  strcat&#40; dir_name, dir_entry_p->d_name &#41;;
	  strcat&#40; dir_name, "/" &#41;; /* Obtaining the full-path eg&#58; /proc/24657/ */

	  if &#40; &#40; dir_proc = opendir&#40; dir_name &#41; &#41; &#41; /* Open that numbered directory */
	    &#123;
	      while &#40; &#40; dir_proc_p = readdir&#40; dir_proc &#41; &#41; &#41; /* Reading its entries */
		&#123;
		  if &#40; strcmp&#40; dir_proc_p->d_name, "exe" &#41; == 0 &#41; /* Check for that exe link file */
		    &#123;
		      strcat&#40; exe_link, dir_name &#41;;
		      strcat&#40; exe_link, dir_proc_p->d_name &#41;; /* Getting the full-path of that exe link */

		      /* Getting the target of the exe ie to which binary it points to */
		      target_link = readlink&#40; exe_link, target_name, sizeof&#40; target_name &#41; &#41;; 
		      target_name&#91; target_link &#93; = '\0';

		      if &#40; strstr&#40; target_name, process &#41; != NULL &#41; /* Searching for process name in the target name */
			&#123;
			  printf&#40; "\n\n%s FOUND --- PROCESS_ID %s \n\n\n", process, process_id &#41;;
			  return atoi&#40;process_id&#41;; /* GOT IT&#58; return the process-id */
			&#125;

		      strcpy&#40; exe_link ,"" &#41;;
		    &#125;
		&#125;
	    &#125;
	  else
	    printf&#40; "Dir %s opening failed \n", dir_name &#41;;
	&#125;
    &#125;

  closedir&#40;dir_p&#41;;
  return 0;
&#125;


int main&#40;&#41;
&#123;
  system&#40; "emacs &" &#41;;
  printf&#40; " %u ", getProcessID&#40; "emacs" &#41; &#41;;
  return 0;
&#125;

getProcessID( ) takes the name of the process, searches inside the /proc directory and returns the process-id. Let me know if there are some other ways.

Mod edit - Added code tags.

[Bedan]

Thanks for the code, really useful!

[jonowoodhouse]

Hi Seranmca

Thanks for this code. It is very useful indeed.

I've made a couple little tweaks and optimisations to it:

unsigned int getProcessID(char *p_processname) {
	DIR *dir_p;
	struct dirent *dir_entry_p;
	char dir_name[40];										// ??? buffer overrun potential
	char target_name[252];									// ??? buffer overrun potential
	int target_result;
	char exe_link[252];
	int errorcount;
	int result;

	errorcount=0;
	result=0;
	dir_p = opendir("/proc/"); 																// Open /proc/ directory
	while(NULL != (dir_entry_p = readdir(dir_p))) {											// Reading /proc/ entries
		if (strspn(dir_entry_p->d_name, "0123456789") == strlen(dir_entry_p->d_name)) {		// Checking for numbered directories 
			strcpy(dir_name, "/proc/");
			strcat(dir_name, dir_entry_p->d_name);
			strcat(dir_name, "/"); 															// Obtaining the full-path eg: /proc/24657/ 
			exe_link[0] = 0;
			strcat(exe_link, dir_name);
			strcat(exe_link, "exe");													 	// Getting the full-path of that exe link
			target_result = readlink(exe_link, target_name, sizeof(target_name)-1);			// Getting the target of the exe ie to which binary it points to
			if (target_result > 0) {
				target_name[target_result] = 0;
				if (strstr(target_name, p_processname) != NULL) {							// Searching for process name in the target name -- ??? could be a better search !!!
					result = atoi(dir_entry_p->d_name);
					printf("getProcessID(%s) :Found. id = %d\n", p_processname, result);
					closedir(dir_p);
					return result;
				}
			}
		}
	}
	closedir(dir_p);
	printf("getProcessID(%s) : id = 0 (could not find process)\n", p_processname);
	return result;
}

Cheers
Jono