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Many new users make mistakes (or have misunderstanding) while applying chmod on files or directories, because of a lack of informative knowledge of:

  • Symbolic notation for ugo and rwx
  • Use of octal numbers

So, in this answer I have provided some useful information that can help to understand correct symbolic notation and using octal numbers.

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  • Maybe you meant that chmod +x [file name] works like chmod 111 [file name] – user579722 Aug 9 '16 at 7:52
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Informative knowledge is provided with the help of The Linux Command-line as refrence/source.

  • First of all it is very essential to know about ugo and rwx manner:

    enter image description here

  • Understanding of attribute which can be out put by ls-l:

    enter image description here

  • Applying Permission:

    enter image description here enter image description here

  • Using Octal number:

    enter image description here

Hence Following work same like:

chmod +rwx [file_name]
chmod 777 [file_name]

And 

chmod 775 [file_name]
chmod ug+rwx,o=rx [file_name]

Hope this helps new users to understand and get knowledge about Symbolic Notation & using Octal number for chmod.

you can download pdf version of linux-command-line book from sourceforge-project

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  • Would it be accurate to say that example chmod ug+rwx,o=rx [file_name] could be chmod a=rwx,o-w [file_name]? Would that be a bad practice? – GaTechThomas Jun 22 '19 at 16:53

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