unix/vncserver

#!/usr/bin/env perl
#
#  Copyright (C) 2009-2010 D. R. Commander.  All Rights Reserved.
#  Copyright (C) 2005-2006 Sun Microsystems, Inc.  All Rights Reserved.
#  Copyright (C) 2002-2003 Constantin Kaplinsky.  All Rights Reserved.
#  Copyright (C) 2002-2005 RealVNC Ltd.
#  Copyright (C) 1999 AT&T Laboratories Cambridge.  All Rights Reserved.
#
#  This is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 2 of the License, or
#  (at your option) any later version.
#
#  This software is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this software; if not, write to the Free Software
#  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307,
#  USA.
#

#
# vncserver - wrapper script to start an X VNC server.
#

#
# First make sure we're operating in a sane environment.
#

$exedir = "";
$slashndx = rindex($0, "/");
if($slashndx>=0) {
    $exedir = substr($0, 0, $slashndx+1);
}

$vncClasses = "";

&SanityCheck();

#
# Global variables.  You may want to configure some of these for your site.
#

$geometry = "1024x768";
#$depth = 16;
$vncJavaFiles = (((-d "$vncClasses") && "$vncClasses") ||
                 ((-d "/usr/share/vnc/classes") && "/usr/share/vnc/classes") ||
                 ((-d "/usr/local/vnc/classes") && "/usr/local/vnc/classes"));
                 
$vncUserDir = "$ENV{HOME}/.vnc";
$skipxstartup = 0;
$xauthorityFile = "$ENV{XAUTHORITY}" || "$ENV{HOME}/.Xauthority";

$xstartup = $vncUserDir . "/xstartup";
$defaultXStartup
    = ("#!/bin/sh\n\n".
       "unset SESSION_MANAGER\n".
       "unset DBUS_SESSION_BUS_ADDRESS\n".
       "OS=`uname -s`\n".
       "if [ \$OS = 'Linux' ]; then\n".
       "  case \"\$WINDOWMANAGER\" in\n".
       "    \*gnome\*)\n".
       "      if [ -e /etc/SuSE-release ]; then\n".
       "        PATH=\$PATH:/opt/gnome/bin\n".
       "        export PATH\n".
       "      fi\n".
       "      ;;\n".
       "  esac\n".
       "fi\n".
       "if [ -x /etc/X11/xinit/xinitrc ]; then\n".
       "  exec /etc/X11/xinit/xinitrc\n".
       "fi\n".
       "if [ -f /etc/X11/xinit/xinitrc ]; then\n".
       "  exec sh /etc/X11/xinit/xinitrc\n".
       "fi\n".
       "[ -r \$HOME/.Xresources ] && xrdb \$HOME/.Xresources\n".
       "xsetroot -solid grey\n".
       "xterm -geometry 80x24+10+10 -ls -title \"\$VNCDESKTOP Desktop\" &\n".
       "twm &\n");

$defaultConfig
    = ("## Supported server options to pass to vncserver upon invocation can be listed\n".
       "## in this file. See the following manpages for more: vncserver(1) Xvnc(1).\n".
       "## Several common ones are shown below. Uncomment and modify to your liking.\n".
       "##\n".
       "# securitytypes=vncauth,tlsvnc\n".
       "# desktop=sandbox\n".
       "# geometry=2000x1200\n".
       "# localhost\n".
       "# alwaysshared\n");

chop($host = `uname -n`);

if (-d "/etc/X11/fontpath.d") {
    $fontPath = "catalogue:/etc/X11/fontpath.d";
}

@fontpaths = ('/usr/share/X11/fonts', '/usr/share/fonts', '/usr/share/fonts/X11/');
if (! -l "/usr/lib/X11") {push(@fontpaths, '/usr/lib/X11/fonts');}
if (! -l "/usr/X11") {push(@fontpaths, '/usr/X11/lib/X11/fonts');}
if (! -l "/usr/X11R6") {push(@fontpaths, '/usr/X11R6/lib/X11/fonts');}
push(@fontpaths, '/usr/share/fonts/default');

@fonttypes = ('misc',
             '75dpi',
             '100dpi',
             'Speedo',
             'Type1');

foreach $_fpath (@fontpaths) {
    foreach $_ftype (@fonttypes) {
        if (-f "$_fpath/$_ftype/fonts.dir") {
            if (! -l "$_fpath/$_ftype") {
                $defFontPath .= "$_fpath/$_ftype,";
            }
        }
    }
}

if ($defFontPath) {
    if (substr($defFontPath, -1, 1) == ',') {
        chop $defFontPath;
    }
}

if ($fontPath eq "") {
    $fontPath = $defFontPath;
}

# Check command line options

&ParseOptions("-geometry",1,"-depth",1,"-pixelformat",1,"-name",1,"-kill",1,
	      "-help",0,"-h",0,"--help",0,"-fp",1,"-list",0,"-fg",0,"-autokill",0,"-noxstartup",0,"-xstartup",1);

&Usage() if ($opt{'-help'} || $opt{'-h'} || $opt{'--help'});

&Kill() if ($opt{'-kill'});

&List() if ($opt{'-list'});

# Uncomment this line if you want default geometry, depth and pixelformat
# to match the current X display:
# &GetXDisplayDefaults();

if ($opt{'-geometry'}) {
    $geometry = $opt{'-geometry'};
}
if ($opt{'-depth'}) {
    $depth = $opt{'-depth'};
    $pixelformat = "";
}
if ($opt{'-pixelformat'}) {
    $pixelformat = $opt{'-pixelformat'};
}
if ($opt{'-noxstartup'}) {
    $skipxstartup = 1;
}
if ($opt{'-xstartup'}) {
    $xstartup = $opt{'-xstartup'};
}
if ($opt{'-fp'}) {
    $fontPath = $opt{'-fp'};
    $fpArgSpecified = 1;
}

&CheckGeometryAndDepth();


# Create the user's vnc directory if necessary.

if (!(-e $vncUserDir)) {
    if (!mkdir($vncUserDir,0755)) {
	die "$prog: Could not create $vncUserDir.\n";
    }
}
    
# Check whether VNC authentication is enabled, and if so, prompt the user to
# create a VNC password if they don't already have one.

$securityTypeArgSpecified = 0;
$vncAuthEnabled = 0;
$passwordArgSpecified = 0;

for ($i = 0; $i < @ARGV; ++$i) {
    # -SecurityTypes can be followed by a space or "="
    my @splitargs = split('=', $ARGV[$i]);
    if (@splitargs <= 1 && $i < @ARGV - 1) {
        push(@splitargs, $ARGV[$i + 1]);
    }
    if (lc(@splitargs[0]) eq "-securitytypes") {
        if (@splitargs > 1) {
            $securityTypeArgSpecified = 1;
        }
        foreach $arg2 (split(',', @splitargs[1])) {
            if (lc($arg2) eq "vncauth" || lc($arg2) eq "tlsvnc"
             || lc($arg2) eq "x509vnc") {
                $vncAuthEnabled = 1;
            }
        }
    }
    if ((lc(@splitargs[0]) eq "-password")
     || (lc(@splitargs[0]) eq "-passwordfile"
     || (lc(@splitargs[0]) eq "-rfbauth"))) {
        $passwordArgSpecified = 1;
    }
}

if ((!$securityTypeArgSpecified || $vncAuthEnabled) && !$passwordArgSpecified) {
    ($z,$z,$mode) = stat("$vncUserDir/passwd");
    if (!(-e "$vncUserDir/passwd") || ($mode & 077)) {
        warn "\nYou will require a password to access your desktops.\n\n";
        system($exedir."vncpasswd -q $vncUserDir/passwd");
        if (($? >> 8) != 0) {
            exit 1;
        }
    }
}
 
# Find display number.

if ((@ARGV > 0) && ($ARGV[0] =~ /^:(\d+)$/)) {
    $displayNumber = $1;
    shift(@ARGV);
    if (!&CheckDisplayNumber($displayNumber)) {
	die "A VNC server is already running as :$displayNumber\n";
    }
} elsif ((@ARGV > 0) && ($ARGV[0] !~ /^-/) && ($ARGV[0] !~ /^\+/)) {
    &Usage();
} else {
    $displayNumber = &GetDisplayNumber();
}

$vncPort = 5900 + $displayNumber;

$desktopLog = "$vncUserDir/$host:$displayNumber.log";
unlink($desktopLog);

# Make an X server cookie - use /dev/urandom on systems that have it,
# otherwise use perl's random number generator, seeded with the sum
# of the current time, our PID and part of the encrypted form of the password.

my $cookie = "";
if (open(URANDOM, '<', '/dev/urandom')) {
  my $randata;
  if (sysread(URANDOM, $randata, 16) == 16) {
    $cookie = unpack 'h*', $randata;
  }
  close(URANDOM);
}
if ($cookie eq "") {
  srand(time+$$+unpack("L",`cat $vncUserDir/passwd`));
  for (1..16) {
    $cookie .= sprintf("%02x", int(rand(256)) % 256);
  }
}

system("xauth -f $xauthorityFile add $host:$displayNumber . $cookie");
system("xauth -f $xauthorityFile add $host/unix:$displayNumber . $cookie"); 

if ($opt{'-name'}) {
    $desktopName = $opt{'-name'};
} else {
    $desktopName = "$host:$displayNumber ($ENV{USER})";
}

# Now start the X VNC Server

$cmd = $exedir."Xvnc :$displayNumber";

my %default_opts;
my %config;

$default_opts{desktop} = &quotedString($desktopName);
$default_opts{httpd} = $vncJavaFiles if ($vncJavaFiles);
$default_opts{auth} = $xauthorityFile;
$default_opts{geometry} = $geometry if ($geometry);
$default_opts{depth} = $depth if ($depth);
$default_opts{pixelformat} = $pixelformat if ($pixelformat);
$default_opts{rfbwait} = 30000;
$default_opts{rfbauth} = "$vncUserDir/passwd";
$default_opts{rfbport} = $vncPort;
$default_opts{fp} = $fontPath if ($fontPath);
$default_opts{pn} = "";

# if a user configuration file already exists
if(stat("$vncUserDir/config")) {

  # loads and parses configuration file
  if(open(IN, "$vncUserDir/config")) {
    while(<IN>) {
      next if /^#/;
      if(my ($k, $v) = /^\s*(\w+)\s*=\s*(.+)$/) {
        $config{$k} = $v;
      } elsif ($_ =~ m/^\s*(\S+)/) {
        $config{$1} = $k;
      }
    }
    close(IN);
  }
}

foreach my $k (sort keys %config) {
  $cmd .= " -$k $config{$k}";
  # user's option takes precedence
  delete $default_opts{$k};
}

foreach my $k (sort keys %default_opts) {
  $cmd .= " -$k $default_opts{$k}";
}

# Add color database stuff here, e.g.:
#
# $cmd .= " -co /usr/lib/X11/rgb";
#

foreach $arg (@ARGV) {
    $cmd .= " " . &quotedString($arg);
}
$cmd .= " >> " . &quotedString($desktopLog) . " 2>&1";

# Run $cmd and record the process ID.

$pidFile = "$vncUserDir/$host:$displayNumber.pid";
system("$cmd & echo \$! >$pidFile");

# Give Xvnc a chance to start up

sleep(3); 
if ($fontPath ne $defFontPath) {
    unless (kill 0, `cat $pidFile`) {
        if ($fpArgSpecified) {
	    warn "\nWARNING: The first attempt to start Xvnc failed, probably because the font\n";
	    warn "path you specified using the -fp argument is incorrect.  Attempting to\n";
	    warn "determine an appropriate font path for this system and restart Xvnc using\n";
	    warn "that font path ...\n";
        } else {
	    warn "\nWARNING: The first attempt to start Xvnc failed, possibly because the font\n";
	    warn "catalog is not properly configured.  Attempting to determine an appropriate\n";
	    warn "font path for this system and restart Xvnc using that font path ...\n";
        }
	$cmd =~ s@-fp [^ ]+@@;
	$cmd .= " -fp $defFontPath" if ($defFontPath);
	system("$cmd & echo \$! >$pidFile");
	sleep(3);
    }
}
unless (kill 0, `cat $pidFile`) {
    warn "Could not start Xvnc.\n\n";
    unlink $pidFile;
    open(LOG, "<$desktopLog");
    while (<LOG>) { print; }
    close(LOG);
    die "\n";
}

warn "\nNew '$desktopName' desktop is $host:$displayNumber\n\n";

# Create the user's xstartup script if necessary.

if (! $skipxstartup) {
    if (!(-e "$xstartup")) {
	warn "Creating default startup script $xstartup\n";
	open(XSTARTUP, ">$xstartup");
        print XSTARTUP $defaultXStartup;
        close(XSTARTUP);
        chmod 0755, "$xstartup";
    }
}

# Create the user's config file if necessary.

if (!(-e "$vncUserDir/config")) {
    warn "Creating default config $vncUserDir/config\n";
    open(XSTARTUP, ">$vncUserDir/config");
    print XSTARTUP $defaultConfig;
    close(XSTARTUP);
    chmod 0644, "$vncUserDir/config";
}

# Run the X startup script.

if (! $skipxstartup) {
    warn "Starting applications specified in $xstartup\n";
}
warn "Log file is $desktopLog\n\n";

# If the unix domain socket exists then use that (DISPLAY=:n) otherwise use
# TCP (DISPLAY=host:n)

if (-e "/tmp/.X11-unix/X$displayNumber" ||
    -e "/usr/spool/sockets/X11/$displayNumber")
{
    $ENV{DISPLAY}= ":$displayNumber";
} else {
    $ENV{DISPLAY}= "$host:$displayNumber";
}
$ENV{VNCDESKTOP}= $desktopName;

system($exedir."vncconfig -nowin >> " . &quotedString($desktopLog) . " 2>&1 &");

if ($opt{'-fg'}) {
    if (! $skipxstartup) {
        system("$xstartup >> " . &quotedString($desktopLog) . " 2>&1");
    }
    if (kill 0, `cat $pidFile`) {
        $opt{'-kill'} = ':'.$displayNumber;
        &Kill();
    }
} else {
    if ($opt{'-autokill'}) {
    	if (! $skipxstartup) {
            system("($xstartup; $0 -kill :$displayNumber) >> "
	     . &quotedString($desktopLog) . " 2>&1 &");
    	}
    } else {
    	if (! $skipxstartup) {
            system("$xstartup >> " . &quotedString($desktopLog)
	     . " 2>&1 &");
    	}
    }
}

exit;


###############################################################################
#
# CheckGeometryAndDepth simply makes sure that the geometry and depth values
# are sensible.
#

sub CheckGeometryAndDepth
{
    if ($geometry =~ /^(\d+)x(\d+)$/) {
	$width = $1; $height = $2;

	if (($width<1) || ($height<1)) {
	    die "$prog: geometry $geometry is invalid\n";
	}

	$geometry = "${width}x$height";
    } else {
	die "$prog: geometry $geometry is invalid\n";
    }

    if ($depth && (($depth < 8) || ($depth > 32))) {
	die "Depth must be between 8 and 32\n";
    }
}


#
# GetDisplayNumber gets the lowest available display number.  A display number
# n is taken if something is listening on the VNC server port (5900+n) or the
# X server port (6000+n).
#

sub GetDisplayNumber
{
    foreach $n (1..99) {
	if (&CheckDisplayNumber($n)) {
	    return $n+0; # Bruce Mah's workaround for bug in perl 5.005_02
	}
    }
    
    die "$prog: no free display number on $host.\n";
}


#
# CheckDisplayNumber checks if the given display number is available.  A
# display number n is taken if something is listening on the VNC server port
# (5900+n) or the X server port (6000+n).
#

sub CheckDisplayNumber
{
    local ($n) = @_;

    socket(S, $AF_INET, $SOCK_STREAM, 0) || die "$prog: socket failed: $!\n";
    eval 'setsockopt(S, &SOL_SOCKET, &SO_REUSEADDR, pack("l", 1))';
    if (!bind(S, pack('S n x12', $AF_INET, 6000 + $n))) {
	close(S);
	return 0;
    }
    close(S);

    socket(S, $AF_INET, $SOCK_STREAM, 0) || die "$prog: socket failed: $!\n";
    eval 'setsockopt(S, &SOL_SOCKET, &SO_REUSEADDR, pack("l", 1))';
    if (!bind(S, pack('S n x12', $AF_INET, 5900 + $n))) {
	close(S);
	return 0;
    }
    close(S);

    if (-e "/tmp/.X$n-lock") {
	warn "\nWarning: $host:$n is taken because of /tmp/.X$n-lock\n";
	warn "Remove this file if there is no X server $host:$n\n";
	return 0;
    }

    if (-e "/tmp/.X11-unix/X$n") {
	warn "\nWarning: $host:$n is taken because of /tmp/.X11-unix/X$n\n";
	warn "Remove this file if there is no X server $host:$n\n";
	return 0;
    }

    if (-e "/usr/spool/sockets/X11/$n") {
	warn("\nWarning: $host:$n is taken because of ".
             "/usr/spool/sockets/X11/$n\n");
	warn "Remove this file if there is no X server $host:$n\n";
	return 0;
    }

    return 1;
}


#
# GetXDisplayDefaults uses xdpyinfo to find out the geometry, depth and pixel
# format of the current X display being used.  If successful, it sets the
# options as appropriate so that the X VNC server will use the same settings
# (minus an allowance for window manager decorations on the geometry).  Using
# the same depth and pixel format means that the VNC server won't have to
# translate pixels when the desktop is being viewed on this X display (for
# TrueColor displays anyway).
#

sub GetXDisplayDefaults
{
    local (@lines, @matchlines, $width, $height, $defaultVisualId, $i,
	   $red, $green, $blue);

    $wmDecorationWidth = 4;	# a guess at typical size for window manager
    $wmDecorationHeight = 24;	# decoration size

    return if (!defined($ENV{DISPLAY}));

    @lines = `xdpyinfo 2>/dev/null`;

    return if ($? != 0);

    @matchlines = grep(/dimensions/, @lines);
    if (@matchlines) {
	($width, $height) = ($matchlines[0] =~ /(\d+)x(\d+) pixels/);

	$width -= $wmDecorationWidth;
	$height -= $wmDecorationHeight;

	$geometry = "${width}x$height";
    }

    @matchlines = grep(/default visual id/, @lines);
    if (@matchlines) {
	($defaultVisualId) = ($matchlines[0] =~ /id:\s+(\S+)/);

	for ($i = 0; $i < @lines; $i++) {
	    if ($lines[$i] =~ /^\s*visual id:\s+$defaultVisualId$/) {
		if (($lines[$i+1] !~ /TrueColor/) ||
		    ($lines[$i+2] !~ /depth/) ||
		    ($lines[$i+4] !~ /red, green, blue masks/))
		{
		    return;
		}
		last;
	    }
	}

	return if ($i >= @lines);

	($depth) = ($lines[$i+2] =~ /depth:\s+(\d+)/);
	($red,$green,$blue)
	    = ($lines[$i+4]
	       =~ /masks:\s+0x([0-9a-f]+), 0x([0-9a-f]+), 0x([0-9a-f]+)/);

	$red = hex($red);
	$green = hex($green);
	$blue = hex($blue);

	if ($red > $blue) {
	    $red = int(log($red) / log(2)) - int(log($green) / log(2));
	    $green = int(log($green) / log(2)) - int(log($blue) / log(2));
	    $blue = int(log($blue) / log(2)) + 1;
	    $pixelformat = "rgb$red$green$blue";
	} else {
	    $blue = int(log($blue) / log(2)) - int(log($green) / log(2));
	    $green = int(log($green) / log(2)) - int(log($red) / log(2));
	    $red = int(log($red) / log(2)) + 1;
	    $pixelformat = "bgr$blue$green$red";
	}
    }
}


#
# quotedString returns a string which yields the original string when parsed
# by a shell.
#

sub quotedString
{
    local ($in) = @_;

    $in =~ s/\'/\'\"\'\"\'/g;

    return "'$in'";
}


#
# removeSlashes turns slashes into underscores for use as a file name.
#

sub removeSlashes
{
    local ($in) = @_;

    $in =~ s|/|_|g;

    return "$in";
}


#
# Usage
#

sub Usage
{
    die("\nusage: $prog [:<number>] [-name <desktop-name>] [-depth <depth>]\n".
	"                 [-geometry <width>x<height>]\n".
	"                 [-pixelformat rgbNNN|bgrNNN]\n".
	"                 [-fp <font-path>]\n".
	"                 [-fg]\n".
	"                 [-autokill]\n".
	"                 [-noxstartup]\n".
	"                 [-xstartup <file>]\n".
	"                 <Xvnc-options>...\n\n".
	"       $prog -kill <X-display>\n\n".
	"       $prog -list\n\n");
}


#
# List
#

sub List
{
    opendir(dir, $vncUserDir);
    my @filelist = readdir(dir);
    closedir(dir);
    print "\nTigerVNC server sessions:\n\n";
    print "X DISPLAY #\tPROCESS ID\n";
    foreach my $file (@filelist) {
	if ($file =~ /$host:(\d+)$\.pid/) {
	    chop($tmp_pid = `cat $vncUserDir/$file`);
	    if (kill 0, $tmp_pid) {
		print ":".$1."\t\t".`cat $vncUserDir/$file`;
	    } else {
		unlink ($vncUserDir . "/" . $file);
	    }
	}
    }
    exit 1;
}


#
# Kill
#

sub Kill
{
    $opt{'-kill'} =~ s/(:\d+)\.\d+$/$1/; # e.g. turn :1.0 into :1

    if ($opt{'-kill'} =~ /^:\d+$/) {
	$pidFile = "$vncUserDir/$host$opt{'-kill'}.pid";
    } else {
	if ($opt{'-kill'} !~ /^$host:/) {
	    die "\nCan't tell if $opt{'-kill'} is on $host\n".
		"Use -kill :<number> instead\n\n";
	}
	$pidFile = "$vncUserDir/$opt{'-kill'}.pid";
    }

    if (! -r $pidFile) {
	die "\nCan't find file $pidFile\n".
	    "You'll have to kill the Xvnc process manually\n\n";
    }

    $SIG{'HUP'} = 'IGNORE';
    chop($pid = `cat $pidFile`);
    warn "Killing Xvnc process ID $pid\n";

    if (kill 0, $pid) {
	system("kill $pid");
	sleep(1);
	if (kill 0, $pid) {
	    print "Xvnc seems to be deadlocked.  Kill the process manually and then re-run\n";
	    print "    ".$0." -kill ".$opt{'-kill'}."\n";
	    print "to clean up the socket files.\n";
	    exit
	}

    } else {
	warn "Xvnc process ID $pid already killed\n";
	$opt{'-kill'} =~ s/://;
    
	if (-e "/tmp/.X11-unix/X$opt{'-kill'}") {
	    print "Xvnc did not appear to shut down cleanly.";
	    print " Removing /tmp/.X11-unix/X$opt{'-kill'}\n";
	    unlink "/tmp/.X11-unix/X$opt{'-kill'}";
	}
	if (-e "/tmp/.X$opt{'-kill'}-lock") {
	    print "Xvnc did not appear to shut down cleanly.";
	    print " Removing /tmp/.X$opt{'-kill'}-lock\n";
	    unlink "/tmp/.X$opt{'-kill'}-lock";
	}
    }

    unlink $pidFile;
    exit;
}


#
# ParseOptions takes a list of possible options and a boolean indicating
# whether the option has a value following, and sets up an associative array
# %opt of the values of the options given on the command line. It removes all
# the arguments it uses from @ARGV and returns them in @optArgs.
#

sub ParseOptions
{
    local (@optval) = @_;
    local ($opt, @opts, %valFollows, @newargs);

    while (@optval) {
	$opt = shift(@optval);
	push(@opts,$opt);
	$valFollows{$opt} = shift(@optval);
    }

    @optArgs = ();
    %opt = ();

    arg: while (defined($arg = shift(@ARGV))) {
	foreach $opt (@opts) {
	    if ($arg eq $opt) {
		push(@optArgs, $arg);
		if ($valFollows{$opt}) {
		    if (@ARGV == 0) {
			&Usage();
		    }
		    $opt{$opt} = shift(@ARGV);
		    push(@optArgs, $opt{$opt});
		} else {
		    $opt{$opt} = 1;
		}
		next arg;
	    }
	}
	push(@newargs,$arg);
    }

    @ARGV = @newargs;
}


#
# Routine to make sure we're operating in a sane environment.
#

sub SanityCheck
{
    local ($cmd);

    #
    # Get the program name
    #

    ($prog) = ($0 =~ m|([^/]+)$|);

    #
    # Check we have all the commands we'll need on the path.
    #

 cmd:
    foreach $cmd ("uname","xauth") {
	for (split(/:/,$ENV{PATH})) {
	    if (-x "$_/$cmd") {
		next cmd;
	    }
	}
	die "$prog: couldn't find \"$cmd\" on your PATH.\n";
    }

    if($exedir eq "") {
      cmd2:
	foreach $cmd ("Xvnc","vncpasswd") {
	    for (split(/:/,$ENV{PATH})) {
		if (-x "$_/$cmd") {
		    $vncClasses = "$_/../vnc/classes";
		    next cmd2;
		}
	    }
	    die "$prog: couldn't find \"$cmd\" on your PATH.\n";
	}
    }
    else {
      cmd3:
	foreach $cmd ($exedir."Xvnc",$exedir."vncpasswd") {
	    for (split(/:/,$ENV{PATH})) {
		if (-x "$cmd") {
		    $vncClasses = $exedir."../vnc/classes";
		    next cmd3;
		}
	    }
	    die "$prog: couldn't find \"$cmd\".\n";
	}
    }

    #
    # Check the HOME environment variable is set
    #

    if (!defined($ENV{HOME})) {
	die "$prog: The HOME environment variable is not set.\n";
    }
#    chdir($ENV{HOME});

    #
    # Find socket constants. 'use Socket' is a perl5-ism, so we wrap it in an
    # eval, and if it fails we try 'require "sys/socket.ph"'.  If this fails,
    # we just guess at the values.  If you find perl moaning here, just
    # hard-code the values of AF_INET and SOCK_STREAM.  You can find these out
    # for your platform by looking in /usr/include/sys/socket.h and related
    # files.
    #

    chop($os = `uname`);
    chop($osrev = `uname -r`);

    eval 'use Socket';
    if ($@) {
	eval 'require "sys/socket.ph"';
	if ($@) {
	    if (($os eq "SunOS") && ($osrev !~ /^4/)) {
		$AF_INET = 2;
		$SOCK_STREAM = 2;
	    } else {
		$AF_INET = 2;
		$SOCK_STREAM = 1;
	    }
	} else {
	    $AF_INET = &AF_INET;
	    $SOCK_STREAM = &SOCK_STREAM;
	}
    } else {
	$AF_INET = &AF_INET;
	$SOCK_STREAM = &SOCK_STREAM;
    }
}