Unix permissions (chmod)

Three ways of writing the same permissions: boxes, a number (755) and letters (rwxr-xr-x, as in ls -l). Change any of them, the others follow, with the chmod command and what it allows.

Permissions
read rwrite wexecute x
Owner
Group
Others

Command

As ls -l shows it:

With the number

    
With letters (same result, easier to reread)

    

    
What it allows

    
    

  


  

    

      umask
      
The umask removes permissions from new files and directories. Type yours (the umask command shows it) to see what you get.

      
      

      

        
New file

        
New directory

      

    

  


  

    
Transparency

    
Everything is computed in your browser, by the scripts listed below. Nothing you type leaves this page.

    

      
Enforced by your browser

      
This page's Content Security Policy allows a single destination, the site's audience measurement (connect-src https://stats.r-no.fr, see below), and forbids any form submission (form-action 'none'), so even a bug could not send what you type anywhere. You can read the policy at the top of the page source.
Audience measurement
Like every page of the site, this one counts its visit with Umami, installed on R-no’s own server (stats.r-no.fr). It receives the address of the page, without parameters or anchor, the site you came from (its domain only), your browser, system, language and screen size, and the country, region and city deduced from your IP address, which is not kept. It never receives what you type, nor the result of the tool. No cookie, nothing stored in your browser; if your browser asks not to be tracked (Do Not Track), nothing is measured. The data is erased after 25 months.
  • /commun/mesure.js: the filter applied before each sending, written for R-no Toolbox. 1.4 kB
    SHA-256 225eec74fd12623d82fc05ee7d222be629ce454d081c129e8d1e249ed37ee716
  • https://stats.r-no.fr/m.js: Umami’s tracker, open source (MIT), served by the measurement server. Its fingerprint is not shown here: it changes with each version of Umami, and you cannot check from your browser that it is the published code. For that part, you have to trust R-no.


      
What is stored

      
No cookie, and nothing in the address. What you type is never stored: it disappears when you reload or close the page. Your language is given by the address itself (/en/ or /fr/): nothing is stored to remember it. Like any website, the server records the download of the page and its files in its access logs (IP address, date and time, address requested, browser name). It never receives what you type.


      
Code that runs here

      

        
    
          
  • app.js: the conversions, explanations and warnings, written for R-no Toolbox. Not minified, no third-party library. 14.4 kB
    SHA-256 cc489f1953da4454ccd6d40e1da11d8c125420a6a8073db7387ab9613113053f
    • 
          
  • textes.js: the French messages of the tool, shown by its script (the rest of the French page is written into its HTML when the site is built). It only defines texts, with no logic. 9.0 kB
    SHA-256 5a5eecceb23b9245491d5fb68f21733332299434be36754becc083f881567e86
    • 
          
  • /commun/langue.js: the language helper, the same on every page of the site. It reads the language of the page and gives the tool its messages in that language. It stores nothing. 1.6 kB
    SHA-256 80f76f69773ef628d36d09bf8387cfedebda4529210d7120649b6f5603310631
    • 
        

      


      
Before you paste

      
This page only writes text: it runs nothing, neither here nor on your machine. What you paste into a terminal or a configuration file runs with your rights, so read it first. The code it writes downloads nothing and calls no outside service.


      
How it was checked

      
On a Linux machine, for 586 of the 4,096 possible modes (every seventh one): both commands were run, stat read back the exact mode, and ls -l printed the same letters as the tool, which reads them back to the same mode.


      
Check it yourself

      
Download a script and compare its fingerprint with the one above:
curl -s https://r-no.fr/linux/chmod/app.js | shasum -a 256


      
Limits

      
Classic Unix permissions only: ACLs (setfacl, the + after the letters), SELinux contexts and macOS extended attributes can allow or forbid more. chmod needs to be run by the owner or root. On a directory, GNU chmod keeps an existing setgid bit when given 3 digits; write 5 digits (00755) to remove it.