at

at time

This takes commands and executes them later, at a given time. Users are only permitted to use this command if their name appears in the file /usr/lib/cron/ at.allow or does not appear in the file /usr/lib/cron.at.deny. If the latter is empty, any user can invoke the command. If neither file is present, only root is allowed to use the command. Its use is a little strange. The commands that are to be executed later are piped into the at command. The results are not immediately displayed on the screen, but are available by typing the mail command. This displays the standard output and error data from the at command.

$ echo "ls -alsi"  at now +1 minutejob 669444240.a at Wed Mar 20 04:44:00 1991$ dateWed Mar 20 04:47:03 GMT 1991$ mailFrom root Wed Mar 20 04:44 GMT 1991total 36204 1 drwxr-xr-x 2 root sys 2 Mar 20 04:18 .201 3 drwxr-xr-x 23 root sys 1440 Feb 5 04:23 ..577 1 -rw-r-r- 1bin bin 56 Apr 6 1989 .proto1532 0 prw-- 1 root root 0 Mar 20 04:43 FIFO578 1 -rw-r-r- 1 bin bin 18 Apr6 1989 at.allow579 1 -rw-r-r- 1 bin bin 18 Apr 6 1989 cron.h*********************************************Cron: The previous message is the standard output and standard error of one of your cron commands.

crontab

crontab [file]

crontab -d

crontab -l

crontab allows the user to execute commands automatically by scheduling their execution at a certain time and...