What's a simple way to run a command, say, 8 hours from now? I can think of this way:
nohup bash -c "sleep 28800 ; ./mycommand.sh" &
Is there a more "proper" way?
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You can use the
at command. The
at execute commands at a later time. The
at utility shall read commands from standard input and group them together as an at-job, to be executed at a later time.
at is installed by default in Ubuntu, but if your release doesn't include it, install via:
sudo apt-get install at
For more information, options, examples, and others, see the manpage in
man 1 at.
Example of a relative time specification (note the space between
+ and the duration):
at now + 8 hours -f ~/myscript.sh
You can also use convenient shorthands, like
noon, as in
echo "tweet fore" | at teatime
Note: This will run the command to the left of the pipe immediately - and its output (which is piped to
at) will be run by
at at the scheduled time. So, the above command schedules
tweet fore to be run at teatime.
The example also demonstrates how you can pipe actions into
at -c is the way you can examine scheduled actions, which you can conveniently list with their number, as with:
at -c 3
Use the Gnome-based GUI for
at, and the like:
The introduction of the CronHowto suggests using the
gnome-schedule gui, which is much nicer than typing all the garbage into the terminal (esp. for "average" Ubuntu users who are not "power" *nix/bsd users.)
Run it by using the Unity Dash (or other applications menu) to look for Scheduled Tasks or running
On Gnome-based Ubuntu systems Gnome Scheduled tasks tool (from the gnome-schedule package) in Applications --> System Tools provides a graphical interface with prompting for using Cron. The project website is at http://gnome-schedule.sourceforge.net/; the software is installable from the Software Center or by typing
sudo apt-get install gnome-schedule
in a terminal.
gnome-schedule, for a script in your home directory, a new "at" command would be set up using this type of window:
Yes, you can set a cron job.
For example if now the time is 14:39:00 and today is friday, 30 august, you can add the following cron job (to be executed after 8 hours) in your crontab file using
crontab -e command:
39 22 30 8 5 /path/to/mycommand.sh
I figured out a quick and dirty way to do this before I found out
at was a thing.
Say you want your script to run at noon:
until [[ "$(date)" =~ "12:00:" ]]; do sleep 10 done ./mycommand.sh
Say you want it to run tomorrow at noon (today is Nov 24 for me):
until [[ "$(date)" =~ "25 12:00:" ]]; do sleep 30 done ./mycommand.sh
Update: Slightly better method: only test the numbers you care about, using
until [[ $(date +%H:%M) == 21:06 ]]; do ...