chmod 644-rw-r--r--
chmod 644 lets the owner read and write a file while everyone else can only read it — the standard default for regular, non-executable files.
Owner
You, the file's creator
Group
Everyone in the file's group
Public
Everyone else on the system
Special permissions(advanced, rarely needed)
Common presets
On a file, 644 means the owner can view and edit it, and everyone else can view it but not change it or run it as a program. This is the default permission for HTML, CSS, JavaScript, images, and most configuration or text files that need to be publicly readable.
644 is almost never appropriate for a directory. Without the execute bit, nobody — not even the owner in practice — can enter the directory or reach a file inside it by path, even though the directory listing itself might technically be readable. If you need a directory with the same read/write intent, use 755 (public) or 750 (group-restricted) instead.
When to use chmod 644
Use 644 for the everyday files a website or application serves: source files, assets, and config that need to be readable by the web server and by other users on the box, but shouldn't be edited by anyone except their owner.
Security notes
644 is a safe default for public files. Never use it for anything containing secrets — API keys, credentials, or private config — since it makes the file readable by every local user. Use 600 for those instead.