chmod 755-rwxr-xr-x
chmod 755 gives the owner full read, write, and execute access, while the group and everyone else can read and execute but not modify.
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, 755 means the owner can edit and run it, while everyone else can read it and run it — but not change it. This is the standard mode for scripts, compiled binaries, and CGI programs that need to be executable by anyone using the system but should only be editable by whoever owns them.
On a directory, the execute bit controls whether a user can enter it and access files inside by name. 755 lets the owner create, rename, and delete anything inside, while the group and everyone else can enter the directory and list its contents, but can't add, remove, or rename files there themselves.
When to use chmod 755
755 is the default you reach for on a web server's document root, a script or binaries directory, or almost any project folder that doesn't hold secrets — content the public should be able to read and, for scripts, execute, but that only the owning user should be able to change.
Security notes
This is safe for genuinely public content, since no one outside the owner can write to it. It's a poor fit for anything sensitive, though: 755 on a directory means anyone on the system can browse its contents, so pair it with correct file-level permissions if some files inside shouldn't be world-readable.