What chmod 777 does, why it is risky, and the safer 755 or 644 to use instead
Runs in your browser. Nothing you type is sent anywhere. Updated on 24 Oct 2026.Chmod 777 gives the owner, the group and every other user on the system read, write and execute: rwxrwxrwx. Any account or compromised process can then change or replace the file, so it is almost never the right fix for a permission error. Give the file to the right owner instead, and use 755 for scripts and directories or 644 for ordinary files. Shared folders such as /tmp use 1777, with the sticky bit.
Open the page with 777 already set: rwxrwxrwx.
Read the warning under the breakdown: anyone on the system can change or replace the file.
Untick Write for Group and Others to get 755, or type 644 for a plain file.
Type the file name in File or directory and press Copy for the safer chmod command.
This chmod calculator converts Unix and Linux file permissions between the octal number, such as 755, and the symbolic letters that ls -l prints, such as rwxr-xr-x. Tick the read, write and execute boxes for the owner, the group and everyone else, type a number, or paste the permission column from ls -l, including the leading file type letter; all three stay in step.
The command line underneath is ready to copy, in numeric form (chmod 755 file) or symbolic form (chmod u=rwx,g=rx,o=rx file), with -R for a whole directory tree and your file name quoted for the shell if it contains spaces. Warnings appear for modes that are usually a mistake, such as a world-writable file.
The umask box shows what a umask does to new files, which start from 666, and new directories, which start from 777. A umask of 022 gives 644 and 755; 077 gives 600 and 700.
The rest of the article, and all 6 questions about Chmod Calculator, are on the Chmod Calculator page.
The owner gets 7, which is read (4) plus write (2) plus execute (1). The group and everyone else get 5, read plus execute. So anyone can run the program or open the directory, but only the owner can change it. In ls -l it appears as rwxr-xr-x.
Both let only the owner write. 755 adds execute for everyone, which a script, a program or a directory needs; 644 leaves execute off, which suits ordinary files such as web pages, images and configuration. Giving a plain file 755 is harmless but unnecessary.
Mode 777 lets every user on the machine change, replace or delete the file, and run it. On a web server that means any compromised process can rewrite your code. Directories that really must be shared should use 1777, which adds the sticky bit so people can delete only their own files.
Programs normally create files with 666 and directories with 777, and every bit set in the umask is removed. With umask 022, files come out as 644 and directories as 755. With 077 they are 600 and 700, private to the owner. A umask never adds permissions.
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