Checking for process(es)

[Peteris Krumins]

Hello,

Some of the programs i am currently writing (one depends on another) write
their pids to file (create pid files).
Now i want to check if the process is still running by reading the
contents of the pid files and verifying if such pid process exists.

What is the best approach?
- I am thinking of checking if there exists a directory /proc/<pid> for
each pid i want to check if there exists a process.


P.Krumins

[Morris Dovey]

Peteris Krumins wrote:

> Hello,
>
> Some of the programs i am currently writing (one depends on another) write
> their pids to file (create pid files).
> Now i want to check if the process is still running by reading the
> contents of the pid files and verifying if such pid process exists.
>
> What is the best approach?
> - I am thinking of checking if there exists a directory /proc/<pid> for
> each pid i want to check if there exists a process.

Peteris...

I used that approach in my (Linux) code to see if a named
application was running. See [url]http://www.iedu.com/mrd/c/pidof.c[/url]

--
Morris Dovey
West Des Moines, Iowa USA
C links at [url]http://www.iedu.com/c[/url]

[Chuck Dillon]

Peteris Krumins wrote:

> Hello,
>
> Some of the programs i am currently writing (one depends on another) write
> their pids to file (create pid files).
> Now i want to check if the process is still running by reading the
> contents of the pid files and verifying if such pid process exists.
>
> What is the best approach?
> - I am thinking of checking if there exists a directory /proc/<pid> for
> each pid i want to check if there exists a process.
>

First, this approach won't work on all flavors of *NIX systems. You
can do kill(pid,0) to see if the process exists.

However, that doesn't tell you whether the process that exists is in
fact the process you think it is. On some systems and conditions a pid
can be reused quickly so it becomes possible that your pid is referring
to some other process unrelated to what you think it is.

I suggest that you have each process create and lock (man lockf) a file
on a local filesystem. When you want to know if the process exists try
to lock its file. If you can't get the lock the process is still running.

-- ced




--
Chuck Dillon
Senior Software Engineer
NimbleGen Systems Inc.

[Lee]

Use ps command or others similar. Because pid can be reused, the
same pid may mean a totally different process. It is often needed to
gurantee one (only one) instance of your program is running, otherwise
restart it. A common practice is to use file lock. If you are really
dead sure about the pid, you can kill -0 to check its status.

Hope it helps.

Lee

> - I am thinking of checking if there exists a directory /proc/<pid> for
> each pid i want to check if there exists a process.
>
>
> P.Krumins

[Peteris Krumins]

Morris Dovey <mrdovey@iedu.com> wrote in news:3F1CAAA5.80303@iedu.com:

> Peteris Krumins wrote:

>> Hello,
>>
>> Some of the programs i am currently writing (one depends on another)
>> write their pids to file (create pid files).
>> Now i want to check if the process is still running by reading the
>> contents of the pid files and verifying if such pid process exists.
>>
>> What is the best approach?
>> - I am thinking of checking if there exists a directory /proc/<pid>
>> for each pid i want to check if there exists a process.

>
> Peteris...
>
> I used that approach in my (Linux) code to see if a named
> application was running. See [url]http://www.iedu.com/mrd/c/pidof.c[/url]
>

Thanks, this was (and other) examples are very valuable.


P.Krumins