What chmod 644 means
The owner digit is 6, which combines read (4) and write (2). The group digit and other-users digit are both 4, granting read permission only. In symbolic form, 644 is rw-r--r--. The owner can open and edit the file, while everyone else can open it but cannot modify or execute it.
That lack of execute permission is intentional. Text files, images, style sheets, JSON documents, and most configuration files are data rather than programs. Giving them execute permission does not make them easier to read and can make the intended role of the file less clear during audits.
Why websites and configuration files use 644
Static web content commonly uses 644 because the deployment owner needs to update it and the web server only needs to read it. The same pattern works for many system configuration files: root or an administrator owns the file, services can read the settings, and unprivileged users cannot alter them. This keeps routine content available without giving the serving process unnecessary write access.
The mode is appropriate only when world-readable content is acceptable. A public website asset fits that description. A configuration file containing an API token, database password, signing key, or private endpoint may not. Also remember that 644 is usually wrong for directories, because directories need execute permission for traversal; public directories more often use chmod 755.
644 compared with 600
The practical difference between 644 and chmod 600 is who can read the file. Both let the owner read and write, but 600 removes all group and other-user access. Choose 644 when a service or ordinary user legitimately needs to read non-secret content. Choose 600 when disclosure itself is a risk, as with SSH private keys, credential files, personal backups, or token-bearing dotfiles.
File ownership remains important. If the wrong account owns a 644 file, the intended administrator may not be able to update it, while the actual owner still can. Fix the owner or group instead of granting write permission to everyone.
Security and maintenance notes
World-readable does not mean harmless. Before using 644, inspect the file for secrets, internal paths, customer data, or debugging output. Shared teams that genuinely need write access may prefer 664 with a controlled group, but that decision should follow group membership and ownership checks rather than convenience.
Use the chmod calculator to compare 644 with a stricter or group-writable mode. Avoid chmod 777 as a shortcut for a write error: it adds execute and write permissions far beyond what a normal file needs.