How to ensure that only a SINGLE instance of a program runs at a given point of time?

[senzmail]

How do I ensure that only a SINGLE instance of a program runs at a given point of time? For example I want to restrict that only one instance of Firefox runs. System should not allow another instance of Firefox if it is already running.

I also want to know if it is possible to set such a restriction by sysadmin, even if that particular software does not have such an option.

[daverj]

if an application itself does not include a way to do this you could always write a shell wrapper for it which would check for a running instance of the application and either launch or fail based on whether or not it found a running instance. To do this you could use the output of a 'ps -ef | grep ' command. obviously, You would need to know what the ps -ef output is for the application. To make it transparent, you could give the wrapper the same name as the executable and put it in /usr/local/bin and then put /usr/local/bin ahead of the other executable directories in your path; usually /usr/bin.

the following might get you started for a wrapper for firefox. Mind you, it is untested.

cygnus:davidj tmp > cat firefox
#!/bin/bash

ps -ef | grep -v grep | grep firefox > /dev/null
if [ "$?" -eq "1" ]; then
    /usr/bin/firefox &
else
    echo "firefox is already running"
fi

make the script executable, put it in /usr/local/bin.

cygnus:davidj tmp > cd /usr/local/bin
cygnus:davidj bin > sudo chmod a+x firefox
cygnus:davidj bin > ls -l firefox
-rwxr-xr-x 1 root root 157 2007-12-29 12:09 firefox

also make sure /usr/local/bin is before /usr/bin in your path: something like this:

cygnus:davidj tmp > echo $PATH
/bin:/usr/local/bin:/usr/bin:/usr/bin/X11:/usr/games/bin:/usr/X11R6

then when people launch firefox, the script in /usr/local/bin will be found before the executable in /usr/bin.

hope this helps,
davidj

[lazlow]

I think the more important question is, what are you trying to prevent form occurring by doing this? Running multiple instances for Firefox should not be an issue. If it is other programs at issue there are probably easier ways to prevent those issues.