Unix chmod Command

This page lists the permissions, references and operators that can be used with the chmod Command. *Note that below are not all the possible combinations of the command.

          chmod (or change mode) is a very useful tool that can be used to edit what users can do with a specific file. Although chmod can be dangerous if it is not used correctly, below are the options that you can use with chmod.
Permission Mode Binary Value
Read privileges r 100
Write privileges w 010
Execute privileges x 001
          This table cotains the references (how to set user/group specific permissions) that will be used with chmod
Reference Class Description
u user Allows only the owner of the file to have certain permissions.
g group Allows only users who are members of the file's group to have certain permissions.
o others Allows users who are not the owner of the file or members of the group to have specific permissions.
a all Encompasses all three of the above.
          These are chmod operators that allow the user (owner of the file) to add or take away permissions.
Operator Description
+ Adds the specified mode to a file or directory
- Takes away the specified mode to a file or directory.
Code Output

chmod a+rwx

         This gives all users and groups read, write and execute privileges.

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chmod a-rwx

         This takes away all read, write, and execute privileges for all users

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chmod +r

         This will give all users the ability to read the file. Using chomod a+r will do the same thing, and is considered to be the "correct" way to do it. With this said, both ways work. It is best to use a if you want to change the permission for all of the users.

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chmod a+x

         This gives all users the ability to execute the file.

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chomod u-x

         This will only give the root or super user the ability to execute the file.

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