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Sat, Feb 14, 2015 11:19 pm

Determining image information from the command line on OS X using file

For a file that is an image, you can determine the type of image from a shell prompt, e.g., from a Terminal window, on an OS X system using the file command:

$ file menu_button
menu_button: PNG image data, 18 x 18, 8-bit/color RGB, non-interlaced

For PNG images, the command will also reveal the size of the image, e.g., for the example above the image is 18 pixels wide by 18 pixels high. The first number is the width and the second number is the height, though in this case the height equals the width.

The command can be useful if a file has a missing extension or if you need to verify that the file extension matches the actual image type.

The command determines the type of image stored in a file from a "magic number" stored near the beginning of the file. For PNG images, the PNG file header, which is the first 8 bytes of the file, will contain ASCII 89 P N G cr nl sub nl. CR represents a carriage return (octal 15, decimal 13, hexadecimal 0D) and NL represents a newline, aka line feed, character (decimal 10, octal 12, hexadecimal 0A). ASCII SUB is octal 032, decimal 26 and hexadecimal 1A. The first character before "PNG" is octal 211, which is decimal 137 and hexadecimal 89.

You can see the characters at the beginning of the file using the od utility, which is a filter which displays the specified files, or standard input if no files are specified, in a specified format. Supported formats include octal, decimal, hexadecimal, or ASCII. E.g, to display the first 8 bytes of a file in ASCII format, you can use the -a option to display the data in ASCII format and the -N option to display only the first 8 bytes.

$ od -a -N 8 menu_button 
0000000   89   P   N   G  cr  nl sub  nl                                

The 89 is the hexadecimal number for the first byte; that is 137 in decimal and 211 in octal. The first 8 bytes in octal format are shown below:

$ od -b -N 8 menu_button 
0000000   211 120 116 107 015 012 032 012                                

The hexdump command with the -C ("C" stands for "canonical") option can be used to display both hexadecimal and ASCII output at the same time.

$ hexdump -C -n 8 menu_button
00000000  89 50 4e 47 0d 0a 1a 0a                           |.PNG....|

For GIF files, file displays the size of the image with the first number, 165 in the example below, being the width and the second number, 57, being the height.

$ file home.gif
home.gif: GIF image data, version 89a, 165 x 57

File can determine that a file is a GIF file because for a GIF file the first 6 characters of the file will be ASCII GIF87a.

$ od -a -N 6 home.gif
0000000    G   I   F   8   9   a                                        

You can display both the hexadecimal and ASCII characters with the hexdump command using the -C option.

$ hexdump -C -n 6 home.gif
00000000  47 49 46 38 39 61                                 |GIF89a|

For JPG files, the file command won't display the image dimensions, but will display any comments stored within the image.

$ file A12.jpg
A12.jpg: JPEG image data, JFIF standard 1.01, comment: "Processed By eBay with ImageMag"

The first two bytes of a JPG file are hexadecimal FF D8 and the last two bytes in the file are hexadecimal FF D9

$ hexdump -n 2 A12.jpg
0000000 ff d8                                          
$ hexdump A12.jpg
<text snipped>
00047c0 17 b2 96 08 0b 42 70 10 38 01 33 45 d0 7f ff d9

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Sat, Feb 14, 2015 4:43 pm

Correcting "Windows Installer Service could not be accessed" Problem

When I tried to install Norton Ghost 7.5 on a Windows Small Business Server (SBS) 2003 server, I received the message below:
Windows Installer
The Windows Installer Service could not be accessed.
This can occur if you are running Windows in safe
mode, or if the Windows Installer is not correctly
installed. Contact your support personnel for assistance.

[ OK ]

I downloaded Windows Installer 3.1 Redistributable (v2) From Microsoft's Download Center and installed it, but I got the same results when I tried to reinstall Symantec Ghost 7.5.

Microsoft's article, "Error 1719: The Windows Installer service could not be accessed" error message when you try to add or remove a program states the behavior may occur if the following conditions are true:

I was starting the Symantec Gost 7.5 installation process from a CD with an autorun file, but I noticed there was a file, Symantec Ghost.msi in an Install directory on the CD. The installation process likely uses the .msi file for the installation.

Microsoft's article recommends steps to resolve the problem. You should first determine the location of the file msiexec.exe on your system. The file will be in the Windows system32 directory, which is usually either C:\Windows\system32 or C:\WINNT\system32 for versions of Windows after Windows 98. For Windows 98 the file is usually in C:\Windows\System. You can search for the file or you can determine the Windows directory by obtaining a command prompt and checking the value of the %WINDIR% environment variable with echo %WINDIR%, which will tell you which directory is the Windows directory on a system. You can then verify that msiexec.exe is in that directory.

C:\>dir %WINDIR%\system32\msiexec.exe
 Volume in drive C has no label.
 Volume Serial Number is E88C-7773

 Directory of C:\Windows\system32

03/21/2005  02:00 PM            78,848 msiexec.exe
               1 File(s)         78,848 bytes

You then need to check the registry to make sure that HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSIServer\ImagePath has a value that corresponds to the actual location of the msiexec.exe file on the system. You can do so using the regedit command or using a reg query command from a command prompt.

C:\>reg query HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSIServer

    Description    REG_SZ    Adds, modifies, and removes applications provided a
s a Windows Installer (*.msi) package. If this service is disabled, any services
 that explicitly depend on it will fail to start.
    Type    REG_DWORD    0x20
    Start    REG_DWORD    0x3
    ErrorControl    REG_DWORD    0x1
    ImagePath    REG_EXPAND_SZ    C:\Windows\system32\msiexec.exe /V
    DisplayName    REG_SZ    Windows Installer
    DependOnService    REG_MULTI_SZ    RpcSs
    DependOnGroup    REG_MULTI_SZ
    ObjectName    REG_SZ    LocalSystem


If the msiexec.exe file is in C:\Windows\System32, you should see C:\Windows\System32\Msiexec.exe /V as the value in the key. In the case of the system I was working on, the file location matched the registry value.

If the values don't match, you will need to enter the correct path in the registry or put the file in the directory listed in the registry. Once the values match, you will need to reregister the msiexec.exe file. To do so, restart the computer in Safe Mode (hit F8 to get the menu of boot options before Windows starts when you reboot).

Once you've logged into an administrator account on the system in Safe Mode, you will need to use the following procedure:

Click Start, click Run, type the following line, and then click OK:

msiexec /regserver

Note: For 64-bit operating systems, you also need to reregister the 64-bit MSI installer. To do this, click Start, click Run, type the following line, and then click OK:

Drive:\Windows\Syswow64\Msiexec /regserver

On 64-bit editions of a Windows operating system, 32-bit binaries are located in %systemroot%\SysWow64 folder. 64-bit binaries are located in the %systemroot%\System32 folder.

Once you have reregistered the msiexec.exe file, you will need to reboot into standard mode. Then try the installation process again that failed previously. If that fails, Microsoft does offer another alternative for dealing with the problem. See "Method 2" at "Error 1719: The Windows Installer service could not be accessed" error message when you try to add or remove a program.

In my case, I was then able to successfully reinstall Symantec Ghost 7.5 on the system, though I did receive another error at the end of the process that was not associated with the previous installer problem. The error I received at the end is shown below.

Symantec Ghost Configuration Server
08001 [Sybase[[ODBC driver][Adaptive Server Anywhere]Unable to connect to
database server: Database server not running

[ OK ]


  1. Windows Installer 3.1 Redistributable (v2)
    Date Published: September 2, 2005
    Microsoft Download Center
  2. "Error 1719: The Windows Installer service could not be accessed" error message when you try to add or remove a program
    Article ID : 315346
    Last Review : March 1, 2007
    Microsoft Help and Support
  3. File Extension Details for .MSI

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