Clock changes of more than 3 hours are considered to be corrections to the clock, and the new time is used immediately.In Debian and Redhat cron treats the files in /etc/cron.d as extensions to the /etc/crontab file (they follow the special format of that file, i.e. The intended purpose of this feature is to allow packages that require finer control of their scheduling than the /etc/cron.directories allow to add a crontab file to /etc/cron.d.Such files should be named after the package that supplies them.Note that comments are not allowed on the same line as cron commands, since they will be taken to be part of the command.Similarly, comments are not allowed on the same line as environment variable settings.You should use absolute path names for commands like /bin/ls. Crontab is the program used to install, deinstall or list the tables used to drive the cron daemon in Vixie Cron.
The value string is not parsed for environmental substitutions, thus lines like: PATH = $HOME/bin:$PATH will not work as you might expect.If the time has moved forwards, those jobs which would have run in the time that was skipped will be run soon after the change.Conversely, if the time has moved backwards by less than 3 hours, those jobs that fall into the repeated time will not be re-run.Another note: the LOGNAME variable is sometimes called USER on BSD systems... In addition to LOGNAME, HOME, and SHELL, cron will look at MAILTO if it has any reason to send mail as a result of running commands in "this" crontab.If MAILTO is defined (and non-empty), mail is sent to the user so named.