Verify a checksum in OS X

Edited by Rich, Eng, Anonymous

The OS X operating system offers two built in methods to verify the checksum of a downloaded file. A checksum is a sequence of numbers and letters which is derived from a newly created file. The checksum of a download can be compared to that of the original file to determine if data is missing. Missing data corrupts files, any corrupt file will not run correctly. Checking the checksum before working with large downloaded files can reduce the time spent troubleshooting.

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Instructions

  1. 1
    Find the checksum.
    Return to the web page you downloaded the file from. The site will list the SHA-1 or MD5 value of the file. Copy this value to a blank text document.
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  2. 2
    MD5.
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    1. Open Terminal.  
      1. Shortcut. Hold the command key down and press space to open Spotlight.
      2. Search for terminal in spotlight
    2. Type openssl md5 in terminal. Do not press enter yet.
    3. Enter file path. At this point you can drag and drop the file into the terminal to add the file path automatically. Otherwise, you need to type the entire path to the file manually.
    4. Interpreting output. The openssl md5 command will output the following: MD5(filename)= value.
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  3. 3
    SHA-1.
     
    1. Open Terminal. Follow the instructions above to open the terminal window.
    2. Type openssl sha1 in the terminal window. Do not press enter yet.
    3. Enter the file path. Drag and drop the file into the terminal window to copy the file path into the command. This will save you an immense amount of time.
    4. Interpreting the output. Output will read: SHA1(filename)= value.
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  4. 4
    Comparing checksum.
    After either operation, copy the checksum into the same text document as the first step. Copy the value directly underneath the initial value. Compare the two values; If they are the same then the file downloaded correctly.
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Tips Tricks & Warnings

  • Apple Official Downloads. Official downloads from Apple are automatically checked for SHA-1 verification by the system. No need to perform the check yourself.
  • If you have problems with any of these steps, ask a question for more help, or post in the comments section below.

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Article Info

Categories : Operating System

Recent edits by: Eng, Rich

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