/usr/share/zsh/help/ttyctl is in zsh-common 5.1.1-1ubuntu2.3.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | ttyctl [ -fu ]
The -f option freezes the tty (i.e. terminal or terminal emula-
tor), and -u unfreezes it. When the tty is frozen, no changes
made to the tty settings by external programs will be honored by
the shell, except for changes in the size of the screen; the
shell will simply reset the settings to their previous values as
soon as each command exits or is suspended. Thus, stty and sim-
ilar programs have no effect when the tty is frozen. Freezing
the tty does not cause the current state to be remembered:
instead, it causes future changes to the state to be blocked.
Without options it reports whether the terminal is frozen or
not.
Note that, regardless of whether the tty is frozen or not, the
shell needs to change the settings when the line editor starts,
so unfreezing the tty does not guarantee settings made on the
command line are preserved. Strings of commands run between
editing the command line will see a consistent tty state. See
also the shell variable STTY for a means of initialising the tty
before running external commands.
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