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I'm writing a wake on lan script for a set of our lab computers. We have sqlite db with a list of the computer hostnames, IPs, and MACs and currently I ping each of them with '-c1' so it doesn't run endlessly - but even that takes some waiting, is there a quicker way to get answer rather than ping? Using ping seems to slow the script quite a bit as it needs the ping answers to continue.
Thanks much for any suggestions!
Sending a single packet and waiting for a response is going to be one of the fastest possible ways, and ping is a fine way to do that. In fact, depending on your use case, I'd argue that it's too fast, since it doesn't really tell you if the system is actually doing anything useful, just that the kernel's network subsystem is alive and configured.
But assuming that's good enough, you can make some improvements. First, you could use -W1 to decrease the ping timeout to one second. Second, you could make your script ping the different hosts asynchronously (in a background thread), and check the results as needed rather than waiting.
Alternately, you can re-think the approach and have the remote systems check in somehow when they're up, and if a system hasn't checked in, you can assume it's down.
This is what fping was designed for. http://fping.sourceforge.net/
You need to parse the output afterwards instead of relying on a return code, but it is much faster than doing normal ping.
This would only work for one or two computers, but if you connect them directly to the computer responsible for checking their status, you can use ethtool to see if the link is active or not.
ethtool {network_interface} | grep "Link detected" | cut -f 3 -d ' ' will return yes if a machine is connected, and no if it is not.
Feb 21, 2011 at 17:04
What you could do it ping the broadcast address which should cause all the computers to ping back. Then you could cross check this list against what you have in SQLite to ensure all the computers are up.
Other then that a ping is probably the fastest way to ensure a computer is awake on a network. As mentioned by the other answer this doesn't provide any really useful data. If you have the ability to install scripts you can add a cronjob to ping a central server, run a task, or just echo out the process list to a central server which will log the request. Then simply checking that will tell you if you have any issues with no need to manually check every time.
Ganglia uses multicast traffic to monitor many hosts in a cluster, perhaps you could use something similar? This assumes that your networking hardware allows multicast traffic between all the hosts and your monitoring system.
I had the same problem and came up with the following (quick & dirty) script. This esentially issues all pings as separate jobs in parallel and will scan an an entire /24 subnet in 3 seconds; note that for some reason I did not bother to find out I could not use the ping result code here but grep -v did the job:
#!/bin/bash
case $# in
1)
case $1 in
[1-9]*)
echo
echo Systems active in subnet: $1
for (( K = 1 ; K < 255 ; K=$K+1 )); do
# grep -v delivers 0 on no matches
echo -ne "testing:" $1$K "... \r"
(if ping -c 1 -w 1 -n $1$K 2>&1 | grep -q '64 bytes' ; then
echo $1$K alive " "
fi) &
done
sleep 3
echo " "
exit 0
;;
esac;;
esac
In C,
/* count = 1, wait interval = 1 second, no name lookup, */
/* 10 data bytes, 1 second timeout, 200 millisecond wait time */
sprintf(command,"ping -c1 -i1 -n -s10 -t1 -W200 %u"
, connection[port].IPAddress);
err = system(command);
/* err == 0 means OK */
I've found fping -r0 ... to provide the fastest response.
The -r (retry) option seems faster than the similar -c (count). Using -r0 results in just one ping being sent and the output is much abbreviated compared to other options.
On my system...
fping -r0 PRINTER LX00 LX01 LX02 LX03 HA01 2>&1
Results in...
LX00 is alive
LX02 is alive
HA01 is alive
ICMP Host Unreachable from 192.168.1.5 for ICMP Echo sent to LX01
PRINTER is unreachable
LX01 is unreachable
LX03 is unreachable
A little massaging to get rid of the ICMP message(s) gives me...
fping -r0 PRINTER LX00 LX01 LX02 LX03 HA01 2>&1 | grep ' is ' | sort
HA01 is alive
LX00 is alive
LX01 is unreachable
LX02 is alive
LX03 is unreachable
PRINTER is unreachable
As for speed, the fping on this old 1.8GHz Intel Dual-Core with 4GB RAM is...
time fping -r0 PRINTER LX00 LX01 LX02 LX03 HA01 2>&1
LX00 is alive
LX02 is alive
HA01 is alive
PRINTER is unreachable
LX01 is unreachable
LX03 is unreachable
real 0m0.554s
user 0m0.000s
sys 0m0.000s
And the grep and sort seem to only add 0.001-0.004s to the time...
time fping -r0 PRINTER LX00 LX01 LX02 LX03 HA01 2>&1 | grep ' is ' | sort
HA01 is alive
LX00 is alive
LX01 is unreachable
LX02 is alive
LX03 is unreachable
PRINTER is unreachable
real 0m0.558s
user 0m0.000s
sys 0m0.000s
NOTES
ICMP message doesn't occur on every run.2>&1 is necessary to prevent the ICMP message from
showing up in the output as it is sent to stderr instead of stdout.