Shell Programming and Scripting

Code:

while sleep 1; do
pgrep Polo || {
                  kill `pidof Polo` >/dev/null 
    
    /var/bin/polo_start.sh start &
    echo `date` R >> /var/log/Check_Polo .log
    }
done
exit 0

well , i use that script as a watchdog in my box (with has just 32 mb memory) which check every second if Polo binary is not running , it would start it. this works functionally right here.
but the problem is , it always use memory for sleep 1 command (since my box has a few memory and this watchdog is always running so it's really important for me to save memory of them ) as in top command always shows:

Code:

Command                                %MEM  
sleep 1                                4.7% 
[pgrep]                                 5 %

i need expert advice , how to change or improvw my script (esp those command) to would not use memory for sleep 1, ... or on the other words use least memory resources. would really appreciate any helps.

P.s : Linux 2.6.23.17_stm23_A21 #1 PREEMPT sh4 GNU/Linux
and pgrep , ... comes from busybox.
Best Regards.

As an alternate to sleep, have you considered using ping? Read the man page appropriate to your OS and define it to ping the local host twice. This usually takes one second, but do check it. Various OS have different options, so you might have one of the following:-

Code:

ping -c2 localhost >/dev/null 2>&1
ping -n 2 localhost >/dev/null 2>&1
ping -c 2 -t 1 localhost  >/dev/null 2>&1

I'm not sure if that is lighter on memory, but it's worth a try.


I hope that this helps,
Robin
Liverpool/Blackburn

I have no experience with busybox (that I'm aware of) and haven't used linux very much during the past few years. That said, I think you may be overestimating the memory impact of running sleep.

All of sleep's code, the text segment of the executable, is already in ram since the shell running that script is the same exact binary. Since sleep, pgrep, pidof, date, echo, kill, sh, sleep, et al, are all instances of the busybox binary (only thing that differs is the name used to exec them), the kernel is able to run many instances of the binary using only a single copy of their code (the memory management subsystem maps that single copy of the text segment into each process' address space).

By the way, ping is also busybox, so that won't save anything (it will probably hurt a bit, as a ping is more complicated than a sleep).

Resorting to a non-busybox binary that isn't already in use will certainly be counterproductive. Its text segment is not shared with another extant process and so it will consume an amount of ram equal to its size (whereas a shared text segment consumes nearly nothing for each additional instance of that binary).

Are you certain you have a problem?

Regards,
Alister

Thanks both guys for reply.
alister , u are right , ping not save any memory even it use a bit more than sleep. (i tested it) .

Are you sure that 4.7% is right? Are you sure that percent doesn't count shared memory? That sounds inflated...

solved

Pooyair, rather than just leaving a cryptic message "solved", it would be nice to tell people how you solved the problem.