Re: Check if a process exists? (EXTENDING THE QUESTION)

Re: Check if a process exists? (EXTENDING THE QUESTION)

[lucianolnx]

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Today, what are the bests ways to know if a deamon is running without 
knowing its PID ? 

My old technique (used until now), is based on recovering the PID saved by 
the own process in a special and known location (like a file), almost all 
times persisted (PERSISTENCE IS A PROBLEM). 

Luciano 



On Tue, 1 Mar 2005, Hareesh Nagarajan wrote: 

> Hi, 
> 
> Can a process check if a given PID exists or not? In other words can a 
> process check if an unrelated process is alive? Is there any system 
> call that does this? 
> 
Use kill() with a second argument being zero. 

    if (kill(pid, 0) == -1) 
    { 
       /* Process is not there. */ 
    } 
    else 
    { 
       /* Process is alive. */ 
    } 

Holger 

Re: Check if a process exists? (EXTENDING THE QUESTION)

[M.Baris Demiray]

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lucianolnx wrote:
> Today, what are the bests ways to know if a deamon is running without 
> knowing its PID ? 

I'm not sure whether this is `the best way' but you can parse some proc
file system entry. Especially /proc/$pid/cmdline and /proc/$pid/status
will be useful. And you will have to search all the /proc/$pid entries
since you don't know the pid..

For example, they provide following information for clamd.

[baris@rhinox]$ ps aux|grep clamd
clamav     424  0.0  3.1  11520  7856 ?        Ss   01:35   0:03 
/usr/sbin/clamd
clamav    1184  0.0  3.1  11520  7856 ?        S    09:38   0:00 
/usr/sbin/clamd
baris     1238  0.0  0.2   1688   712 pts/2    S+   09:58   0:00 grep clamd
[baris@rhinox]$ cat /proc/1184/cmdline
/usr/sbin/clamd
[baris@rhinox]$ cat /proc/1184/status
Name:   clamd
State:  S (sleeping)
Tgid:   1184
Pid:    1184
PPid:   424
....
....

I also should add that /proc filesystem is _optional_ in configuration.
Highly likely it will exist on a target system but a little possibility
of being it unselected still there.

> My old technique (used until now), is based on recovering the PID saved by 
> the own process in a special and known location (like a file), almost all 
> times persisted (PERSISTENCE IS A PROBLEM). 
> 
> Luciano 

-- 
"You have to understand, most of these people are not ready to be
unplugged. And many of them are no inert, so hopelessly dependent
on the system, that they will fight to protect it."
                                                         Morpheus

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Re: Check if a process exists? (EXTENDING THE QUESTION)

[Ron Michael Khu]

is the daemon/application name unique? maybe u can use a  script that 
makes use of the top-command.
or maybe u can make use of the pstat_getproc() c function.(but im not 
sure if there's a pstat_getproc
func in linux... im using hpux on itanium)

the code below relies on the fact that at any given moment, there is 
only one instance of the
application running...  the code is just a simple-search-and-print.
------------------------------------------------------
  struct pst_status * psa = NULL;
  struct pst_status * prc = NULL;
  struct pst_dynamic  psd;
  long                nproc = 0;
  long                i;

  if ( pstat_getdynamic(&psd, sizeof(psd), 1, 0) == -1 )
    (void)perror("pstat_getdynamic failed");

  nproc  = psd.psd_activeprocs;
  psa    = (struct pst_status *)malloc(nproc * sizeof(struct pst_status));

  if ( pstat_getproc(psa, sizeof(struct pst_status), nproc, 0) == -1 )
    (void)perror("pstat_getproc failed");

  // Report the process info as required
  prc = (struct pst_status *)psa;
  for (i=0; i < nproc; i++)
  {
    if ( strcmp( prc->pst_cmd, "APPLICATION NAME" ) == 0 )
    {
       (void)printf("PID IS %d \n", prc->pst_pid);
       break;
     }
     ++prc;
  }
------------------------------------------------------


lucianolnx wrote:

>Today, what are the bests ways to know if a deamon is running without 
>knowing its PID ? 
>
>My old technique (used until now), is based on recovering the PID saved by 
>the own process in a special and known location (like a file), almost all 
>times persisted (PERSISTENCE IS A PROBLEM). 
>
>Luciano 
>
>
>
>On Tue, 1 Mar 2005, Hareesh Nagarajan wrote: 
>
>  
>
>>Hi, 
>>
>>Can a process check if a given PID exists or not? In other words can a 
>>process check if an unrelated process is alive? Is there any system 
>>call that does this? 
>>
>>    
>>
>Use kill() with a second argument being zero. 
>
>    if (kill(pid, 0) == -1) 
>    { 
>       /* Process is not there. */ 
>    } 
>    else 
>    { 
>       /* Process is alive. */ 
>    } 
>
>Holger 
>  
>