chmod 640 — what rw-r----- means
640
rw-r-----
The owner can read and write; the group can read only; others get nothing.
Permission breakdown
When to use 640
Config or log files that a service group needs to read but the public must not. Common for files owned by you and shared with a daemon's group, like /var/log entries or app config read by a worker group.
Set it with chmod
Apply this permission to a file:
chmod 640 filenameOr apply it recursively to a directory and everything inside it:
chmod -R 640 directory/Other common permissions
Or build any permission with the interactive chmod calculator.