What does the 'umask' command do?

The 'umask' command is used to set default file permissions for newly created files and directories in a Unix-like operating system, including Linux. When a new file or directory is created, the file system applies the umask value to determine the permissions that will be set by default. This is particularly important for managing security, as it allows users to specify whether newly created files should have read, write, or execute permissions for the owner, group, or others.

By default, the system provides a set of maximum permissions when a file or directory is created, and the umask value subtracts permissions from this maximum. For instance, if the default permission is 666 for files (read and write for everyone) and the umask is set to 022, the resulting permission for new files would be 644 (read and write for the owner and read-only for the group and others).

This capability is essential for maintaining the integrity and privacy of files and directories on a multi-user system, ensuring that sensitive data is not accessible to unauthorized users.