os.getlogin() returns the user logged in on the controlling terminal. However
'crontab' only looks for the login name of the process' real user id which
pwd.getpwuid(os.getuid())[0] does provide.
While in most cases there is no difference, the former might fail under certain
circumstances (e.g. a lxc container connected by attachment without login),
throwing the error 'OSError: [Errno 25] Inappropriate ioctl for device'.
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