chmod Calculator – Unix File Permission Calculator

chmod 644 gives the owner read and write permissions while group members and everyone else can only read the file. In symbolic notation this is rw-r--r--. This is the standard permission for regular files like configuration files, HTML files, and documents that should be readable by everyone but only editable by the owner. It is the most commonly used permission set for web server files.

chmod 755 gives the owner full read, write and execute permissions while group members and everyone else can read and execute the file but not write to it. In symbolic notation this is rwxr-xr-x. This is the standard permission for executable files and directories that should be publicly accessible but only modifiable by the owner. Web server directories typically use 755.

Each permission digit represents three binary bits for read, write and execute. Read is worth 4, write is worth 2, and execute is worth 1. You add these values together for each group. So 7 means all three permissions, 6 means read and write, 5 means read and execute, and 4 means read only. A chmod calculator makes this instant by letting you tick checkboxes and showing the number automatically.

chmod stands for change mode. It is a Linux and Unix command used to change the access permissions of files and directories. Every file on a Linux system has permissions controlling who can read it, write to it, or execute it. You specify permissions either as an octal number like 755 or as symbolic notation like rwxr-xr-x.

The execute permission on a file means the system is allowed to run it as a program or script. On a directory, execute permission means the user is allowed to enter the directory and access its contents. Without execute permission on a directory you cannot cd into it even if you can see it listed with ls.

chmod 777 gives every user on the system full read, write and execute permissions. This is almost never appropriate on a production server because it allows any user or process to modify or execute the file. It is occasionally useful for temporary debugging but should never be left on sensitive files or directories in a live environment.