Daemons in llinux

[amityadav]

Can anybody help me to clarify what daemons do in linux

[teenytinylinuxgrl]

A Daemon is the captain of a Ferengi ship isn't it?

LOL, sorry... I love puns. Seriously now:

A daemon is an application that runs in the background like an automatic ClamAv updater or scanner, a bluetooth enabler, network manager, etc.

Amy

[Cabhan]

Moving to a more appropriate forum.

Daemons also frequently are run by the root user at system startup, and their parent is the init process (the very first process run on a Linux system). This allows them to run silently in the background. You cannot generally communicate directly with one, but it is sometimes possible.

Other examples of daemons are sshd (allows you to receive SSH connections), crond (enables the crontab), and cupsd (allows you to print).

[Shutdown]

You cannot generally communicate directly with one, but it is sometimes possible.

I have a question about this comment. Can you go into a little further detail in what you mean by communicate directly? I just want to get the terms right.

For example: sshd

I can stop/start this deamon via:

service sshd stop
service sshd start


Is that what you mean by communicating directly?

Or opening up a terminal and SSHing into a box, would you say by doing so, you are communicating directly with SSHD?

Thanks!

[Kieren]

I can stop/start this deamon via:

service sshd stop
service sshd start


Is that what you mean by communicating directly?

You're not communicating with sshd directly here but communicating through the service application

When you ssh into a computer you are using the service rather than communicating with it. It's a very subtle difference

[Shutdown]

You're not communicating with sshd directly here but communicating through the service application

When you ssh into a computer you are using the service rather than communicating with it. It's a very subtle difference

Subtle indeed!

Ok what about if I did this instead of using the "service" application.



/etc/init.d/sshd stop
/etc/init.d/sshd start



Is that now considered communication with it directly?

[D-cat]

No, that's just starting and killing, which is an OS task. Communicating directly would be something along the lines of changing the daemon's configuration, through the daemon itself (not an application interface), while it was running.

This typically doesn't happen... to the point that I can't come up with an example where it does. (Yes, I know Cups and Privoxy can be reconfigured via the built-in web interfaces, which the closest I can come to an example, but those are still via an application interface). I'm wondering if maybe Samba is a genuine example?

[Shutdown]

No, that's just starting and killing, which is an OS task. Communicating directly would be something along the lines of changing the daemon's configuration, through the daemon itself (not an application interface), while it was running.

This typically doesn't happen... to the point that I can't come up with an example where it does. (Yes, I know Cups and Privoxy can be reconfigured via the built-in web interfaces, which the closest I can come to an example, but those are still via an application interface). I'm wondering if maybe Samba is a genuine example?

Ok, well I think I get the gist of it, the comment about communicating with the daemon directly kinda struck me by surprised....made me think a little bit, probably too much!!!

[Cabhan]

Hehe, what I meant is that the user does not give direct input to the program. One can indeed change the way it operates via configuration files or even theoretically a dbus application of some sort, but daemons are generally the "start and forget" sort of application.