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Re: how can I make sure only one instance of gkrellm runs



On Thu, 2008-10-16 at 15:56 -0700, Antonio Olivares wrote:
> Dear fellow Fedoreans,
> 
> How can I make sure that only one instance of gkrellm runs.  When I start one of my machines run several instances of gkrellm.  I chose in the configuration run only one, but that does not work :(
> 
> [olivares localhost ~]$ whoami 
> olivares                       
> [olivares localhost ~]$ top
> top - 17:51:33 up  1:36,  4 users,  load average: 0.36, 0.50, 0.68
> Tasks: 130 total,   1 running, 129 sleeping,   0 stopped,   0 zombie
> Cpu(s):  4.7%us,  1.0%sy,  0.0%ni, 94.4%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
> Mem:    773348k total,   712732k used,    60616k free,    23792k buffers
> Swap:  3114416k total,       80k used,  3114336k free,   398188k cached
> 
>   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
>  2440 root      20   0  216m  63m 7200 S  3.3  8.4   6:00.98 Xorg
>  2986 olivares  20   0 23088 9832 6528 S  1.0  1.3   0:55.45 gkrellm
>  3008 olivares  20   0 23056 9868 6556 S  1.0  1.3   0:54.94 gkrellm
>  2944 olivares  20   0  103m  23m  15m S  0.7  3.1   0:18.71 plasma
>  2968 olivares  20   0 23088 9832 6528 S  0.7  1.3   0:55.39 gkrellm
>  2978 olivares  20   0 23088 9828 6528 S  0.7  1.3   0:55.75 gkrellm
>  2993 olivares  20   0 23088 9836 6528 S  0.7  1.3   0:55.34 gkrellm
>  3000 olivares  20   0 23088 9832 6528 S  0.7  1.3   0:55.55 gkrellm
>   554 root      15  -5     0    0    0 S  0.3  0.0   0:04.96 scsi_eh_1
>  2936 olivares  20   0 60492  16m  12m S  0.3  2.2   0:07.61 kwin
> 20164 olivares  20   0 73576  15m  11m S  0.3  2.0   0:00.27 konsole
>     1 root      20   0  2016  848  636 S  0.0  0.1   0:04.38 init
>     2 root      15  -5     0    0    0 S  0.0  0.0   0:00.00 kthreadd
> 
> As you can see there are several gkrellm's running :(  
> 
> Cameron shared a script with me:
> 
> #!/bin/bash
> #
> pidfile=$HOME/.grkrellm.pid
>   if [ -s "$pidfile" ] && pid=$(<"$pidfile") && kill -0 "$pid" 2>/dev/null
>   then
>     echo GKrellM already running, pid=$pid, not starting a new one.
>   else
>     gkrellm &           # start gkrellm
>     echo $! >"$pidfile" # save the pid
>   fi
> 
> 
> And it finds that gkrellm is already running so it quits. The script works, but I have to find a way to eliminate the extra gkrellm's.  
> How can I prevent the other gkrellm's and run only one?

1) You don't say how you run the script.
2) What does "kill -0" do? "man kill" doesn't mention this possibilty.
3) The script has an obvious race condition, (i.e. if run from several
places simultaneously, there is a non-zero probability of starting more
than one process). This is because running the process and creating the
pidfile are two separate actions.

poc


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