do something else while waiting for an event, such as reboot

until (ssh root@ 2> /dev/null); do date; sleep 15; done
until (ssh root@ 2> /dev/null); do date; sleep 15; done In this case will execute "date" then "sleep 15" until we are able to ssh into server, such as after a reboot Could also be like: until ( ping 1> /dev/null); do echo "server is down"; sleep 15; done
Sample Output
admin01 00:34 ~/ $ until (ssh root@ 2> /dev/null); do date; sleep 15; done
Tue Mar  8 00:34:57 PST 2011
Tue Mar  8 00:35:12 PST 2011
root@'s password: 
Last login: Mon Mar  7 13:12:20 2011 from server001
[root@somehost ~]#

By: greggster
2011-03-08 08:42:12

What Others Think

Not that it makes any significant difference in this case, but those parentheses around the commands are not necessary. Also, that ping command will go on pinging forever unless you give it a count with the -c option, and as far as I'm aware, GNU ping only sets an error code if it also fails to transmit any packets. Which means, as long as ping's able to transmit its echo requests, 'echo "server is down"; sleep 15' won't run even if ping doesn't receive any responses.
eightmillion · 553 weeks and 4 days ago
yes the ping will need a -c arg - else it will as you say ping forever...
greggster · 476 weeks and 2 days ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

You must be signed in to comment.

What's this? is the place to record those command-line gems that you return to again and again. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.

Share Your Commands

Stay in the loop…

Follow the Tweets.

Every new command is wrapped in a tweet and posted to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning, there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.


Subscribe to the feeds.

Use your favourite RSS aggregator to stay in touch with the latest commands. There are feeds mirroring the 3 Twitter streams as well as for virtually every other subset (users, tags, functions,…):

Subscribe to the feed for: