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A recursive login, as used to be possible in the good old days, no longer works; for most purposes [su](
https://manpages.ubuntu.com/manpages/plucky/man1/su.1.html)
is a satisfactory substitute. Indeed, for security reasons, login does a [vhangup](
https://manpages.ubuntu.com/manpages/plucky/man2/vhangup.2.html) system call to remove
any possible listening processes on the tty. This is to avoid password sniffing. If one uses the command
login, then the surrounding shell gets killed by [vhangup](
https://manpages.ubuntu.com/manpages/plucky/man2/vhangup.2.html) because it’s no longer the true owner of the
tty. This can be avoided by using exec login in a top-level shell or xterm.