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Full Discussion: How to write daemon?
Top Forums Programming How to write daemon? Post 90074 by Perderabo on Friday 18th of November 2005 01:33:34 AM
Old 11-18-2005
I guess that either technique presented in those links is good enough, but I have to say that there is some room for improvement. Both of these techniques are relying on the parent to not make strange mistakes prior to invoking the daemon. We can do a better job of protecting ourself from a insane or hostile parent. By using two forks separated by a setsid() we can create a process that is guaranteed to not have a controlling terminal or even have the ability to accidentally acquire one. I kinda like the idea of closing all possible fd's, but using gettablesize sabotages the idea. gettablesize is basicly a getrlimit(RLIMIT_NOFILE) and is returning the soft limit. You can open a file and then set the soft limit lower...the file won't close or anything. And if the total number of open file is low, you can still open new files. Using sysconf() can avoid that.

Here is a link that gets all of this right 1.7 How do I get my program to act like a daemon? This link is from the Usenet comp.unix.programmer FAQ. From the same FAQ, also see Daemon utility functions. In fact, see the entire FAQ. The whole thing is excellent, despite being a little dated.
 
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rpc.statd(8)						      System Manager's Manual						      rpc.statd(8)

NAME
rpc.statd, statd - Network status monitor daemon SYNOPSIS
/usr/sbin/rpc.statd [-c] OPTIONS
Available only on TruCluster Server systems. This option starts the clusterwide network status daemon, which helps provide highly available NFS service. Do not use -c directly. Highly available NFS service is configured by default and typically does not require intervention. If you do need to start the clusterwide network status daemon, use the CAA command, caa_start cluster_lockd. For more information, see the TruCluster Server Administration manual. DESCRIPTION
The rpc.statd daemon monitors the status of the client and server sites in response to a request made by the local rpc.lockd daemon. When a site failure is detected, the rpc.statd daemon notifies the local rpc.lockd daemon, which then processes the recovery of the locked files or file regions. RESTRICTIONS
The crash of a site is only detected on its recovery. FILES
A directory created by the statd daemon. Each file name in the directory is the host name of a client or server that the statd daemon will notify upon its recovery. A backup directory created by the statd daemon. A file created by the statd daemon to store its state number. SEE ALSO
Daemons: rpc.lockd(8) Files: statmon(4) rpc.statd(8)

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