'chmod' (change mode) is a Unix/Linux command used to change the access permissions of files and directories. In web hosting, it determines who can read, write, or execute a file. Permissions are crucial for security and functionality: setting them correctly ensures that files and scripts run as intended, while protecting sensitive data from unauthorized access. The command uses numeric or symbolic notation to specify permissions for the file owner, group, and others. Proper use of 'chmod' is essential for server management and security.
