Get Process ID for a running application

[bob2oneil]

I need to detemine if an application/daemon is executing under Fedora 64-bit Linux.


The application I need to check I do not have source for, and this is not
the condition of trying to write a singleton solution.

There have been a couple of solutions proposed at the following URLs for
this:

http://developer.qt.nokia.com/forums/viewthread/581

Of the first solution, using the sysctl method, under Fedora, there are
many undefines included KERN_PROC, KERN_PROC_ALL, and kinfo_proc. These
appear to be BSD specific, and it is not clear that the implementation
of sysctl under Fedora Linux would work if I were to cobble together the
BSD header defining these values.

struct kinfo_proc *result, *ptr; 
    int name[] = { CTL_KERN, KERN_PROC, KERN_PROC_ALL, 0 }; 
    size_t length, i; 
    result = NULL; 
    length = 0; 
 
    if (sysctl((int *)name,(sizeof(name)/sizeof(*name)) - 1, NULL, &length, NULL, 0) == -1) 
        return 0;
 
    if ((result = (kinfo_proc *)malloc(length)) == NULL) 
        return 0;
 
    if (sysctl((int *)name, (sizeof(name)/sizeof(*name)) - 1, result, &length, NULL, 0) == -1) 
    {
        free(result);
        return 0;
    }
 
    for (i = 0, ptr = result; (i < (length/sizeof(kinfo_proc)); ++i, ++ptr) 
    { 
        // ptr->kp_proc.p_pid contains the pid 
        // ptr->kp_proc.p_comm contains the name 
        pid_t iCurrentPid = ptr->kp_proc.p_pid;
        if (strncmp(processName, ptr->kp_proc.p_comm, MAXCOMLEN) == 0)  
        {
            free(sProcesses);
            return iCurrentPid;
        }
    } 
 
    free(result);

struct kinfo_proc *result, *ptr; 
    int name[] = { CTL_KERN, KERN_PROC, KERN_PROC_ALL, 0 }; 
    size_t length, i; 
    result = NULL; 
    length = 0; 

    if (sysctl((int *)name,(sizeof(name)/sizeof(*name)) - 1, NULL, &length, NULL, 0) == -1) 
        return 0;

    if ((result = (kinfo_proc *)malloc(length)) == NULL) 
        return 0;

    if (sysctl((int *)name, (sizeof(name)/sizeof(*name)) - 1, result, &length, NULL, 0) == -1) 
    {
        free(result);
        return 0;
    }

    for (i = 0, ptr = result; (i < (length/sizeof(kinfo_proc)); ++i, ++ptr) 
    { 
        // ptr->kp_proc.p_pid contains the pid 
        // ptr->kp_proc.p_comm contains the name 
        pid_t iCurrentPid = ptr->kp_proc.p_pid;
        if (strncmp(processName, ptr->kp_proc.p_comm, MAXCOMLEN) == 0)  
        {
            free(sProcesses);
            return iCurrentPid;
        }
    } 

    free(result);

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Moving on to the next suggested option, was to use a QDirIterator to simply
iterate through the "/proc" file system looking for the executable name or
cmd line which matches my application.

The problem I am having with the 2nd approach is that "/proc" is so heavily
nested and full of content that I blow up my stack as a result of the iteration.

I have something like the following code segment:

QDirIterator it("/proc", QDirIterator::Subdirectories)
while (it.hasNext())
{
	it.next();
	QFileInfo child = it.fileInfo();
 
	if (child.fileName() == ".." || child.fileName() == ".")	
		continue;
 
	...
}

QDirIterator it("/proc", QDirIterator::Subdirectories)
while (it.hasNext())
{
	it.next();
	QFileInfo child = it.fileInfo();

	if (child.fileName() == ".." || child.fileName() == ".")	
		continue;

	...
}

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I am out of ideas, anyone think of some other options or solutions.

Is there a way of scoping QDirIterator so that it only goes 1 level deep?

From what I can tell from inspecting "/proc" on my machine, there are
running daemons for which I know the process id using the task manager,
but inspecting the entries in "/proc" does not show anything for either
the "cmdLine" or "exe" entries, which makes me question if this technique
will work.