Matt [Danger]

Recently I wanted to configure some of our lab computers to automatically configure printers when a user logged on. While reading Apple’s documentation to find a solution I learned about the possible ways to script login procedures in Mac OS X 10.5.

Login Hooks

The first method of scripting a login action is the use of a Login Hook. A Login Hook is a script that is executed immediately after the user logs on but before other login processes are performed. The script runs as root and needs to be chmod’d +x to be made executable. This feature has existed in OS X for some time and is handy for some account specific tasks.

To configure OS X to run your script run the following command as root in Terminal:

defaults write com.apple.loginwindow LoginHook /path/to/script 

This modifies root’s login window properties in /var/root/Library/Preferences/. In Leopard login hooks do not work in any other user or system-wide com.apple.loginwindow preference file. I’m not sure if they did in previous versions.

More information about LoginHooks can be found on Apple’s developer site.

System Login Items (Deprecated)

One of the classrooms I maintain is comprised of 2.4Ghz iMacs (MB323LL/A) that are dual booted with Windows XP and Mac OS X. Sometimes when the workstations are restarted from XP to OS X the display brightness gets changed to its dim power saver setting. This requires the user manually increase the display brightness by pressing the F2 key, which is inconvenient. I haven’t been able to determine the cause of this issue so I wanted to create a login hook to increases the brightness as a temporary fix.

OS X doesn’t ship with a command line utility that let’s you change display brightness. Fortunately, Nicholas Riley has written a utility that uses OS X frameworks to accomplish this quickly and easily. Here’s the code:

#include <stdio.h>
#include <unistd.h>
#include <IOKit/graphics/IOGraphicsLib.h>
#include <ApplicationServices/ApplicationServices.h>
 
const int kMaxDisplays = 16;
const CFStringRef kDisplayBrightness = CFSTR(kIODisplayBrightnessKey);
const char *APP_NAME;
 
void errexit(const char *fmt, ...) {
  va_list ap;
  va_start(ap, fmt);
  fprintf(stderr, "%s: ", APP_NAME);
  vfprintf(stderr, fmt, ap);
  fprintf(stderr, "\n");
  exit(1);
}
 
void usage() {
  fprintf(stderr, "usage: %s [-m|-d display] [-v] <brightness>\n", APP_NAME);
  fprintf(stderr, "   or: %s -l [-v]\n", APP_NAME);
  exit(1);
}
 
int main(int argc, char * const argv[]) {
  APP_NAME = argv[0];
  if (argc == 1)
    usage();
 
  int verbose = 0;
  unsigned long displayToSet = 0;
  enum { ACTION_LIST, ACTION_SET_ALL, ACTION_SET_ONE } action = ACTION_SET_ALL;
  extern char *optarg;
  extern int optind;
  int ch;
 
  while ( (ch = getopt(argc, argv, "lmvd:")) != -1) {
    switch (ch) {
    case 'l':
      if (action == ACTION_SET_ONE) usage();
      action = ACTION_LIST;
      break;
    case 'v':
      verbose = 1;
      break;
    case 'm':
      if (action != ACTION_SET_ALL) usage();
      action = ACTION_SET_ONE;
      displayToSet = (unsigned long)CGMainDisplayID();
      break;
    case 'd':
      if (action != ACTION_SET_ALL) usage();
      action = ACTION_SET_ONE;
      errno = 0;
      displayToSet = strtoul(optarg, NULL, 0);
      if (errno == EINVAL || errno == ERANGE)
	errexit("display must be an integer index (0) or a hexadecimal ID (0x4270a80)");
      break;
    default: usage();
    }
  }
 
  argc -= optind;
  argv += optind;
 
  float brightness;
  if (action == ACTION_LIST) {
    if (argc > 0) usage();
  } else {
    if (argc != 1) usage();
 
    errno = 0;
    brightness = strtof(argv[0], NULL);
    if (errno == ERANGE)
      usage();
    if (brightness < 0 || brightness > 1)
      errexit("brightness must be between 0 and 1");
  }
 
  CGDirectDisplayID display[kMaxDisplays];
  CGDisplayCount numDisplays;
  CGDisplayErr err;
  err = CGGetActiveDisplayList(kMaxDisplays, display, &numDisplays);
  if (err != CGDisplayNoErr)
    errexit("cannot get list of displays (error %d)\n", err);
 
  CFWriteStreamRef stdoutStream = NULL;
  if (verbose) {
    CFURLRef devStdout =
      CFURLCreateWithFileSystemPath(NULL, CFSTR("/dev/stdout"),
				    kCFURLPOSIXPathStyle, false);
    stdoutStream = CFWriteStreamCreateWithFile(NULL, devStdout);
    if (stdoutStream == NULL)
      errexit("cannot create CFWriteStream for /dev/stdout");
    if (!CFWriteStreamOpen(stdoutStream))
      errexit("cannot open CFWriteStream for /dev/stdout");
  }								  
 
  for (CGDisplayCount i = 0; i < numDisplays; ++i) {
    CGDirectDisplayID dspy = display[i];
    CFDictionaryRef originalMode = CGDisplayCurrentMode(dspy);
    if (originalMode == NULL)
      continue;
 
    if (action == ACTION_LIST) {
      printf("display %d: ", i);
      if (CGMainDisplayID() == dspy)
	printf("main display, ");
      printf("ID 0x%x\n", (unsigned int)dspy);
      if (verbose) {
	CFStringRef error = NULL;
	CFPropertyListWriteToStream(originalMode, stdoutStream,
				    kCFPropertyListXMLFormat_v1_0, &error);
	if (error != NULL)
	  errexit("failed to write display info (%s)",
		  CFStringGetCStringPtr(error,
					CFStringGetFastestEncoding(error)));
      }
    }
 
    io_service_t service = CGDisplayIOServicePort(dspy);
    switch (action) {
    case ACTION_SET_ONE:
      if ((CGDirectDisplayID)displayToSet != dspy && displayToSet != i)
	continue;
    case ACTION_SET_ALL:
      err = IODisplaySetFloatParameter(service, kNilOptions, kDisplayBrightness,
				       brightness);
      if (err != kIOReturnSuccess) {
	fprintf(stderr,
		"%s: failed to set brightness of display 0x%x (error %d)",
		APP_NAME, (unsigned int)dspy, err);
	continue;
      }
      if (!verbose) continue;
    case ACTION_LIST:
      err = IODisplayGetFloatParameter(service, kNilOptions, kDisplayBrightness,
				       &brightness);
      if (err != kIOReturnSuccess) {
	fprintf(stderr,
		"%s: failed to get brightness of display 0x%x (error %d)",
		APP_NAME, (unsigned int)dspy, err);
	continue;
      }
      printf("display %d: brightness %f\n", i, brightness);
    }
  }
 
  return 0;
}

You can compile your own utility by saving this code to a file named brightness.c and doing:

gcc -std=c99 -o brightness brightness.c -framework IOKit -framework ApplicationServices

You can also download the precompiled binary.

You can create a login hook to automatically increase the brightness by chmoding the downloaded ‘brightness’ file to 755 and running the following command as root in Terminal:

defaults write com.apple.loginwindow LoginHook "/path/to/brightness 1"

I’m a die hard Mac OS X user and also a lab administrator at a college. Over the years I’ve found several tweaks that help me configure both my personal computer and lab workstations to do different tasks.

Force the printer icon to auto quit after a print job completes. Right-click on the icon and select “Auto Quit” or do:
defaults write /Users/yourusername/Library/Preferences/com.apple.print.PrintingPrefs "Quit When Finished" -bool true

Disable disk checksum verification
defaults write com.apple.frameworks.diskimages skip-verify true

Gradient highlights for Stacks
defaults write com.apple.dock mouse-over-hilte-stack -boolean true

Add recent applications as a Stack on Dock
defaults write com.apple.dock persistent-others -array-add '{ "tile-data" = { "list-type" = 1; }; "tile-type" = "recents-tile"; }

Make extended print dialog show by default
defaults write -g PMPrintingExpandedStateForPrint -bool true

Change the current screenshot format
defaults write com.apple.screencapture type jpg

Disable iTunes store arrows
defaults write com.apple.iTunes show-store-arrow-links -bool false

Stop Safari “saved text” dialogs
defaults write com.apple.Safari DebugConfirmTossingUnsubmittedFormText NO

Force Safari to open all links in new tab
defaults write com.apple.Safari TargetedClicksCreateTabs -bool true

Disable application crash dialogs
defaults write com.apple.CrashReporter DialogType none

Make hidden Dock icons transparent
defaults write com.apple.Dock showhidden -bool true

Disable Dashboard
defaults write com.apple.dashboard mcx-disabled -boolean true

Stop disk image verification
defaults write com.apple.frameworks.diskimages skip-verify true

Enable Data Detectors in 10.5 iChat
defaults write com.apple.iChat EnableDataDetectors true

Modify Sheet Animation
defaults write NSGlobalDomain NSWindowResizeTime .001

Login window tweaks

The text underneath the “Mac OS X” title of the login window will change if you click on it. You can configure the login window to display any of these as default. Valid options are HostName, SystemVersion, SystemBuild, SerialNumber, IPAddress, DSStatus, or Time
defaults write /Library/Preferences/com.apple.loginwindow AdminHostInfo Time

You can add a message to the login window. This is useful in a lab environment when you need to give instructions to your users.
defaults read /Library/Preferences/com.apple.loginwindow LoginwindowText "Some custom message."