Take the 2-minute tour ×
Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

I am using Linux. What is the meaning of chmod 666?

share|improve this question
11  
aka, the Satan command. –  Moab Jun 10 '11 at 21:29
4  
If that bothers you (or if you can't be bothered to remember those numbers) you can also write it as chmod a=rw. –  starblue Jun 11 '11 at 6:48

5 Answers 5

Chmod change attributes from a file/folder

  • chmod 666 means that all users can read and write but cannot execute
  • chmod 777 allows all actions for all users
  • chmod 744 allows only owner to do all actions; group and other users are allowed only to read

    permission to:  owner      group      other     
                    /¯¯¯\      /¯¯¯\      /¯¯¯\
    octal:            6          6          6
    binary:         1 1 0      1 1 0      1 1 0
    what to permit: r w x      r w x      r w x
    
    binary         - 1: enabled, 0: disabled
    
    what to permit - r: read, w: write, x: execute
    
    permission to  - owner: the user that create the file/folder
                     group: the users from group that owner is member
                     other: all other users
    
share|improve this answer
11  
+1 awesome diagram –  Earlz Jun 10 '11 at 21:12
3  
Only it's "octal", not "decimal". +1 anyway. –  Ben Voigt Jun 11 '11 at 14:15
    
oh, sorry, octal! i'll fix this, thanks :) –  kokbira Jun 11 '11 at 23:02
1  
The third point mentioned in the first post is incorrect - chmod 711 allows only owner to do all actions, group and other are allowed only to read ![enter image description here][1] This is the table for rwx for octal rwx 000 001 010 011 100 101 110 111 Octal 001, or 1 denotes execute permission Octal 7, 111 denotes read write and execute permission hence 711 denotes, rwx for owner, and x for groups and others. –  user155250 Aug 29 '12 at 16:04
1  
It only goes to 7 anyway, so there's no difference between octal and decimal in this case. :/ –  Rob Aug 29 '12 at 16:49

In really plain speak: it makes a file read- and write-able by the file owner, the file owner's group and every one else using the machine (all). Applied against a directory it lets everyone read (get file contents lists) of a directory and write (create, edit files in the directory) but not execute files from the directory.

For more detailed information how chmod works check out this handy tutorial.

share|improve this answer
2  
...Don't you mean lets everyone read/write files but not execute, and let's everyone read/write files in a directory, but not list all of the files? –  Earlz Jun 10 '11 at 20:44
2  
what @earlz says, plus write on a dir does not mean you can edit files there (write perms on a file does) but solely means you can create new entries (dirs, files, symlinks, etc.). Also, its nice of you to mention dirs for completeness, but 666 doesn't make sense for a dir; you'd never eliminate x for owner. –  Rich Homolka Jun 10 '11 at 21:01
1  
@Earlz: thanks for that. I always forget what 666 does for dirs because, well, I never set rw- for a user on a dir. :) –  Ian C. Jun 10 '11 at 21:04

As mentioned in other answers, chmod means change mode. It affects the read, write and executable permissions for the owner, group and other categories of users. The numbers that follow the command (in this case 666), indicate how those permissions are modified for the file the command is run on (for 666, it means that owner, group and other have read and write permissions, but no executable permissions).

By changing the numbers to different values you effectively change the permissions for the file. The link I've referenced above has a little tool for figuring out what values you need to put in to get the permissions scheme you're after. It also goes over the switch options available for the command and some examples to help you understand better how it works.

share|improve this answer
1  
That is a great site. It's going in my bookmarks. Thanks! –  Kirk Jun 10 '11 at 21:12

The chmod command (abbreviated from change mode) is a Unix command that lets an operator tell the system how much (or little) access it should permit to a file. Command chmod 666 means that all users will have read and write permissions.

share|improve this answer

If your questions is more about the 666 part than the chmod part, I would refer you to The Linux Documentation Project where is a decent explanation of how file permissions work in Linux.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.