Question

POSIX 2008 says:

A program that uses these functions should be written to catch all
signals and take other appropriate actions to ensure that when the
program terminates, whether planned or not, the terminal device’s
state is restored to its original state.

about using tcgetattr() and tcsetattr() to change the terminal device’s state. In general, which signals need to be handled and what “other appropriate actions” must be taken? If this cannot be answered in general, which signals/actions are appropriate when using tcgetattr() and tcsetattr() to turn off terminal echo?

Answer 1

The point of the comment is that tcsetattr will change the properties of the enclosing terminal. Thus, if you write a program that disables terminal echo and that program exits without resetting the value, then it will be disabled for the duration of the session (unless another program explicitly re-enables it).

The appropriate thing to do is, if you are going to change an attribute, save all of the old values before you change them (and then roll back the changes before exiting). This can be done in a signal handler, which is what the recommendation focuses on.