Which of the following configuration files should be modified to disable the ctrl-alt-delete key combination?

'/etc/keys' is not a standard Linux configuration file and plays no role in key combination handling by init.

'/proc/keys' is a read-only kernel keyring information file that exposes key metadata - it cannot be edited to change key combination behavior.

/etc/inittab is the configuration file read by the SysV init process that defines actions for various runlevel and special events. The line with the 'ctrlaltdel' action keyword tells init what to do when the key combination is pressed - commenting it out or removing it disables the reboot behavior. On systemd systems the equivalent is masking ctrl-alt-del.target, but on traditional SysV systems /etc/inittab is the correct location.

'/proc/inittab' does not exist - the /proc filesystem exposes kernel and process data but does not contain an inittab file.

'/etc/reboot' is not a real configuration file on Linux systems and has no effect on the Ctrl+Alt+Delete key combination.