chmod Quick Reference Summary

The general form of the chmod command: 

   chmod options file

The options are constructed by choosing one from each of these columns, with no blank between them:

WhoOperationPermission
A combination of:
    u user (file owner)
    g group
    o others
    a all (same as ugo) 		Permissions are:
    = assigned
    + added
    - subtracted 		A combination of:
    r read
    w write
    x execute
or one of the following
to copy permissions:
    u user
    g group
    o other
or, to set user id:
    s

Note: Set User ID is usually used only with programs. You may set the s permission for the user or group; people who run the program will then “adopt” the identity of that user or group for the duration of the program.

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