daemonization

daemonization

[xlp]

Hi, I want to understand How can a executale object in Unix can become a "daemon" ? How can it deal with stdout, and ttys it's connected to? What are the C library function I should read man?.


bye

Re: daemonization

[Jan-Benedict Glaw]

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On Fri, 2002-06-28 15:49:13 -0500, xlp <xlp@emtel.net.co>
wrote in message <20020628154913.A377@nietzsche>:
> Hi, I want to understand How can a executale object in Unix can become a "daemon" ? How can it deal with stdout, and ttys it's connected to? What are the C library function I should read man?.

- chdir() to "/"

Most important are these:

- become session leader: setsid()
- fork() and let parent exit(0)
- close() stdin, stdout and stderr and re-open() them with /dev/null
- maybe do a chroot()
- maybe open any IP ports to listen on them
- Drop root privileges: setuid(), setgid()
- Ready (TM)
- Afterwards: At any file you open, don't forget O_NOCTTY!

MfG, JBG
PS: And ___always___ check the return values of those library calls!!!

-- 
Jan-Benedict Glaw   .   jbglaw@lug-owl.de   .   +49-172-7608481
	 -- New APT-Proxy written in shell script --
	   http://lug-owl.de/~jbglaw/software/ap2/

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Re: daemonization

[Glynn Clements]

xlp wrote:

> Hi, I want to understand How can a executale object in Unix can
> become a "daemon" ? How can it deal with stdout, and ttys it's
> connected to? What are the C library function I should read man?.

Daemonisation isn't covered in any particular manual page. However, it
gets its own chapter in Stevens[1].

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

This book is highly recommended, but not cheap (I paid UKP42,
~= EUR60).

However, it doesn't cover sockets; there is another book on network
programming by the same author but, IIRC, it covers both sockets and
TLI, and you're unlikely to need to use TLI.

Jan-Benedict Glaw wrote:

> - chdir() to "/"
> 
> Most important are these:
> 
> - become session leader: setsid()
> - fork() and let parent exit(0)

The fork() comes first; everything else should be done in the child.

> - close() stdin, stdout and stderr and re-open() them with /dev/null

And try to close() all other descriptors.

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