NAME

tcllauncher - Tcl application launcher

SYNOPSIS

::tcllauncher::pidfile_open ?filename? ?mode?

::tcllauncher::pidfile_write

::tcllauncher::pidfile_mtime

::tcllauncher::pidfile_close

::tcllauncher::pidfile_remove

::tcllauncher::daemonize ?-noclose? ?-nochdir?

::tcllauncher::require_user userName

::tcllauncher::require_group groupName

::tcllauncher::require_user_and_group userName groupName

DESCRIPTION

tcllauncher is a way to have Tcl programs run out of /usr/local/bin under their own name, be installed in one place with their support files, and provides commands to facilitate server-oriented application execution.

Now you might think, why bother? I'll just put my script in there and do a #! thing to invoke Tcl.

Well, OK, but this has certain problems:

All your Tcl programs will show in "ps" as tclsh
All your Tcl programs will show in "top" as tclsh
if there are any files you want to pull in that aren't in a package, you have to invent your own place to install and locate them.

You'd like to be able to have stuff show up as its script name.

You could just copy or even link tclsh to the name of your program. Say, for instance, trackserver.

But then you have to invoke trackserver with arguments and do stuff to prep it, like:

    cd ...somewhere...
    /usr/local/bin/trackserver main.tcl

That's the original purpose for tcllauncher, just to make that reasonable.

    cp /usr/local/bin/tcllauncher /usr/local/bin/trackserver
    trackserver

How does it find its files? It cd's to the corresponding lib directory and a directory underneath that of the same name as the application, and sources "main.tcl" with tcl_interactive set to 0.

So when "tcllauncher" is installed as "trackserver" and you run trackserver, what happens "/usr/local/bin/trackserver" starts up like the Tcl shell, except that it sources in "/usr/local/lib/trackserver/main.tcl". Also, a global variable called launchdir is set containing the "launch directory," i.e. the directory where main.tcl was loaded from. ( In the above example, "/usr/local/lib/trackserver.")

WHAT DIRECTORY

Tcllauncher doesn't change your directory behind your back, so wherever you are at when you run it, you're still in that directory.

But a lot of times you want to go to your application directory, so you can just

	cd $::launchdir

Then you can source in all of your various files and stuff like that.

PROCESS GROUP

If you are going to fork off children, exec them, or whatever, you should probably become your own process group so hopefully your children might inherit your signals and Do The Right Thing.

    id process group set

The id command is from the TclX extension.

PID FILE

Lots of apps write a file with the server's process ID in it. Upon relaunch, the program can come along and look in its own pid file to see if it's already alive or not, and also to potentially kill it.

Our pidfile support is a studied Tcl-based copy of BSD's pidfile C library.

::tcllauncher::pidfile_open ?filename? ?mode?

Given an optional path to a pid filename and optional permissions, pidfile_open opens (or creates) a file specified by the path and locks it with TclX's interface to the flock system call.

If the file cannot be locked, the PID of an already running daemon is returned. Otherwise zero is returned and you've got the lock. You can now call pidfile_write to get your pid into the lock file.

This function does not write your process' PID into the file, so it can be used before forking if needed.

If path is not specified (empty string), "/var/run/$::argv0.pid" is used, and if mode is not specified, 0600 is used.

::tcllauncher::pidfile_write

Writes your pid into the pid file previously opened by pidfile_open.

::tcllauncher::pidfile_mtime

Return the mtime of the pidfile.

Can be used after a successful or unsuccessful call to pidfile_open. Considered useful after pidfile_open fails due to another process holding the lock to examine when the owner process got the lock.

::tcllauncher::pidfile_close

Close a pidfile. It should be used after your daemon forks to start a child process.

::tcllauncher::pidfile_remove

Close and remove a pidfile.

EXAMPLE

    set pid [::tcllauncher::pidfile_open "/var/run/daemon.pid" 0600]
    if {$pid > 0} {
	puts stderr "pid $pid already has the lock"
	exit 1
    }
    ::tcllauncher::daemonize
    ::tcllauncher::pidfile_write
    ...do work...
    ::tcllauncher::pidfile_remove
    exit

DAEMONIZE

Sometimes you want your program to spawn itself off into the background in a way that when you logout it doesn't kill the process, etc. To daemonize a tcllauncher app,

::tcllauncher::daemonize ?-noclose? ?-nochdir?

By default this forks off a child and exits the parent. In the child, it changes the current directory to "/", and redirects stdin, stdout and stderr to/from "/dev/null".

Specifying -noclose prevents the closing and redirecting of stdin, stdout and stderr, while -nochdir prevents the changing of the working dir to "/"

This is a rough copy of BSD 4.4's daemon library routine.

USER AND GROUP ID MANAGEMENT

If a program needs to be run as a certain use, it can invoke

::tcllauncher::require_user userName

This requires the program to either be run as fred or as root or something like that, by a user that has permissions to become fred.

If the program is running as user fred or can change the user id (suid) to fred, it continues, else it aborts.

This means if the superuser invokes the program, it will change user to the correct user. If the correct user invokes the program, it will correctly do nothing and proceed. Handy.

::tcllauncher::require_group groupName

does for groups what require_user does for users.

::tcllauncher::require_user_and_group userName groupName

combines changing the group and user into a single procedure.

Note that if you require user first then require group, the process may have lost the privileges necessary to change groups after changing users. Either require the group ID first or use ::tcllauncher::require_user_and_group to do both.

KEYWORDS

background, daemon, daemonize, tcllauncher

COPYRIGHT

Copyright (c) 2007-2014 FlightAware LLC (BSD Liscense)