Unix people generally understand "daemon" to be a long-running process, disconnected from any TTY, perhaps with signal management configured in a particular way.  This corresponds closely to [services under Microsoft Windows NT].

[[... start ...]]










[Tom Poindexter] posted
[http://groups.google.com/groups?q=comp.lang.tcl+poindexter+daemon&hl=en&rnum=5&selm=981010735.778763%40irys.nyx.net]
this example implementation:


 package require Tclx
 proc shutdown {} {
   # whatever cleanup you need to do
   exit
 }

 proc dispatcher {} {
   # do your work here!  this sample just opens a log file and writes to it.
   while 1
     set fd [open /tmp/daemon2.log w]
     puts $fd "daemon2.tcl last ran at [clock format [clock seconds]]" 
     close $fd
     sleep 5
   }
 }
 proc daemonize {} {
   close stdin
   close stdout
   close stderr
   if {[fork]} {exit 0}
   id process group set
   if {[fork]} {exit 0}
   set fd [open /dev/null r]
   set fd [open /dev/null w]
   set fd [open /dev/null w]
   cd /
   umask 022
   return [id process]
 }
 daemonize
 signal ignore  SIGHUP
 signal unblock {QUIT TERM}
 signal trap    {QUIT TERM} shutdown
 dispatcher
Tom wrote this as a Tcl (or, more properly, [TclX]) translation of a
C-coded example which appeared in [W. Richard Stevens]' ''Unix Network
Programming''.  Tom notes that [Expect] also has enough of the POSIX API
"to dissociated from the tty, set umask, become a new process group leader, etc."  In fact,
[BOOK Exploring Expect] devotes an entire chapter to "Background Processing".

[[Explain the "open /dev/null ..."-s ...]]

[[Tom might work on setsid() access (by way of a patch) at some point.]]


TP - changed the 'after 5000' to 'sleep 5', which should work better. 
I noticed some problems with signals and after.  TclX's 'sleep' sets
a traditional Unix alarm(2) ssytem call.  [[Tom, are the problems
something the [after] maintainer should fix?]]










----
    nohup tclsh my_daemon .... &
Is generally useful for "putting a process in the background" while
suppressing SIGHUPs to my_daemon.

And it's even more useful if you redirect stderr/stdout to a file
that is named mnemonically...