daemons

daemons

[ameer armaly]

Hi all.
What do I need to do to have a program invoke as a daemon; i.e sit and ait
for a particular event to happen, and then do something, all in the
background?
Thanks,



Ameer

Re: daemons

[Glynn Clements]

ameer armaly wrote:

> What do I need to do to have a program invoke as a daemon; i.e sit and ait
> for a particular event to happen, and then do something, all in the
> background?

The topic of daemon processes gets its own chapter in Stevens[1], but
the short version is:

1. Call fork(), and have the parent exit.

2. Call setsid() to create a new session and disconnect from the
   controlling terminal.

3. Call chdir() to change the current directory to the daemon's
   working directory, or the root directory if it doesn't have one.

4. Call umask(0) to reset the file permissions mask.

5. Close all unused file descriptors.

[1] Advanced Programming in the Unix(R) Environment
    W Richard Stevens
    Addison-Wesley

Depending upon what the daemon does, other useful steps may include:

6. Reset the environment to a fixed set of values.

7. Set up descriptors 0, 1 and 2 (use /dev/null if nothing else is
   appropriate).

8. Reset other aspects of the process' environment which will have
   been inherited, e.g. resource limits.

-- 
Glynn Clements <glynn.clements@virgin.net>

Re: daemons

[Alphex K.]

On Sat, 14 Feb 2004 23:14:45 -0500 (EST)
ameer armaly <ameer@charter.net> wrote:

So, You can do it =)
You must call the fork(),close all enviroment and so all =)
some like this

//closing the enviroment
int pid;
if((pid=fork())==0)
{
for(;;)
{
// something useful
}
}

so, it's all
---===---
Alphex Kaanoken
Senior developer of Crew IT research labs
web: http://crew.org.ru
mailto:Alphex@Crew.Org.RU