chmod Calculator NZ
This calculator translates Unix and Linux file permissions between their octal form, such as 755, and their symbolic form, such as rwxr-xr-x, and explains what each part means. File permissions control who can read, write and run a file, and they are a constant source of confusion because they are written two different ways. The octal form is three digits, one each for the owner, the group and everyone else, where each digit is the sum of 4 for read, 2 for write and 1 for execute. The symbolic form spells out the same thing as nine letters, r, w and x or dashes, in three groups. Setting permissions with the chmod command means knowing the number you want, and reading a directory listing means decoding the letters, so being able to convert between them quickly is genuinely useful. This tool does it. You enter a three-digit octal permission, and the calculator shows the symbolic form, then breaks it down into what the owner, the group and others can each do. The result updates as you type. Use it to work out the chmod number for the permissions you want, to understand a permission string from a file listing, or to learn how Unix permissions work. Each octal digit from 0 to 7 maps to a combination of read, write and execute: 7 is read, write and execute, 5 is read and execute, 4 is read only, and so on. The common 755 means the owner can do everything while the group and others can read and run but not change the file, which is typical for programs and directories. 644 means the owner can read and write while others can only read, typical for ordinary files. Knowing these patterns makes managing permissions much easier.
Each octal digit = 4 (read) + 2 (write) + 1 (execute), for owner, group and others. 755 = rwxr-xr-x; 644 = rw-r--r--. Enter a 3-digit octal value.
How it works
Each of the three octal digits, for the owner, group and others, is read as a sum of 4 for read, 2 for write and 1 for execute. The calculator turns each digit into its three permission letters, r, w and x, or dashes where the permission is absent, building the nine-character symbolic string and spelling out what each class of user can do.
Worked example
The octal permission 755 breaks into 7, 5 and 5. The 7 is 4 plus 2 plus 1, so the owner has read, write and execute, shown as rwx. Each 5 is 4 plus 1, so the group and others have read and execute, shown as r-x. Together that is the symbolic permission rwxr-xr-x.
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