What chmod 755 grants
The first digit belongs to the owner. A 7 combines read (4), write (2), and execute (1), so the owner receives rwx. The second and third digits are both 5, combining read (4) and execute (1) for the group and all other users. The complete permission string is rwxr-xr-x: only the owner can modify the item.
Execute means different things for files and directories. On a file, it allows the operating system to run the file as a program or script. On a directory, it allows a user to enter the directory and reach items inside it. Directory read permission controls whether names can be listed, so read and execute are commonly granted together on public directory trees.
Typical directory and web server uses
755 is common for directories that serve public application code, static assets, or documentation. A deployment account can update the directory, while a web server process can traverse it and read its contents without receiving write access. The same mode also fits scripts and binaries that users need to run but should not edit.
Do not assume that an entire website should be recursively set to 755. Regular HTML, CSS, JavaScript, image, and configuration files usually do not need execute permission. Upload or cache directories may need carefully scoped write access for a service account, but that is better solved with correct ownership or group permissions than by making the whole web root writable.
755 compared with 644
A familiar web layout uses 755 for directories and chmod 644 for ordinary files. Both modes let other users read content, but 755 adds execute permission. That execute bit is necessary for directory traversal and executable programs; it is unnecessary on a normal document. Setting a directory to 644 often breaks access because users can see names but cannot traverse the directory reliably.
For private material, neither 755 nor 644 is appropriate because both expose content to other users. Credentials and private keys generally need chmod 600 or a similarly restrictive mode.
Security checks before using 755
755 is safer than chmod 777 because group members and other users cannot write. It is not private, however: other users may read a file or traverse a directory. Confirm that the content is intended to be visible, verify who owns it, and avoid applying permissions recursively until you know which entries are files and which are directories.
Use the chmod calculator to test a narrower combination when an application needs something different. Start with the least access that allows the process to work, then add a specific group permission rather than opening access to everyone.