Everyone knows and loves screen for running longtime scripts in the background without worrying that the ssh connection will drop and will have to run it again. Still, I have found myself many times in the situation where I started a process and needed to put it in the background and run something else on the console. Uff.. If only I started it with screen. But wait, there is hope. This quick tip will show how to put a process in the background and then start it back in foreground.

This works in bash and uses the ‘suspend‘ key (CTRL+Z) and the bg – background and fg – foreground commands. Let’s say we were running an intensive rsync command, and are wanted to check if we still have the available space on the disk without opening a new ssh session (yes, I know):
rsync -ar server:/source/ /destination/
^Z
Stopped

Let it run in the background:
bg
[1] rsync -ar server:/source/ /destination/ &

Now we can run some other commands like du:
du -h

We can see the background process with ps or jobs:
jobs
[1] Running rsync -ar server:/source/ /destination/

And finally we can bring it back to foreground with fg:
fg

Note: this works only on the running ssh/bash session and it will be closed once you exit. Logout should warn about open/running jobs and that they will be lost if exit.

Here is a quick bash tip that might be useful if you need to use inside a bash script a check to see if a wildcard expression of files/folders exists or not. For example:

if [ -e /tmp/*.cache ]
then
echo "Cache files exist: do something with them"
else
echo "No cache files..."
fi
This is using -e (existing file check) that is working fine on individual files. Also the above code might seem to work fine if the result of the expression if one file; but if you have more files returned by the expression this will fail with the following error:
line x: [: too many arguments

Read the rest of this entry »

This post will show how to deal with the issue I had on a newly installed debian lenny xen virtual machine. I used xen-tools to create the vm using the deboostrap method, and all was fine. I installed the bash-completion package, as probably most of you, I can’t live without bash completion, but quickly found out that it was broken. Any attempt to perform a filelist completion was failing with this error:
vm11:~# tail -f /va<TAB>-bash: /dev/fd/62: No such file or directory
-bash: /dev/fd/60: No such file or directory
and this basically makes the bash completion useless. On a quick look I could easily see that the /dev/fd link was not there and that was the main cause of the problem. Still on one older lenny vm I had for a couple of months this was not happening (from what I can tell because it had an older version of the /etc/bash_completion file). There are several ways to fix this starting with the obvious one to downgrade /etc/bash_completion but I didn’t like that, so I looked for some other ways. Read the rest of this entry »