monitor host for slow ping times

When there is intermittent network latency to a host, it’s important to monitor a it for a pattern. Using ping can help narrow down what is causing the latency. VMWare load, bandwidth limitations, employee work patterns, backups, and many other sources could be the cause of the latency.

while true; do j=`ping <slowhost> -i1 -c1 2>&1 | grep icmp_req | awk '{print $7}' | cut -d = -f2 | cut -d . -f1`; if [ $j -gt 30 ]; then date | tr '\n' ' ';  echo $j; fi; sleep 1s; done;

This does a ping every second, and if it’s over a threshold (30ms in this case) it is considered unacceptable and logged with date.

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monitor host for connectivity

Sometimes, you want to be notified if a host goes up or down. Usually Nagios is perfect for this, but in this case I had an internet circuit, and all I cared about was knowing when the ISP deactivated it. Use ping in a loop, make 1 request every second, if ping doesn’t get a response, then send a text message (Verizon number) and stop the loop.

while true; do ping -nc 1 -W 1 5.6.7.8 | grep -q icmp; if [ "$?" == "1" ]; then echo "circuit is down" | mail <10-digit phone number no spaces>@vtext.com; break; fi; sleep 1s; done;

I also use the converse of this method when I want to know when a new circuit comes up.

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find fastest Ubuntu mirror with netselect

Using some internal metrics, netselect can tell you what mirror is “best” for you to use for downloading packages, or setting up your own mirror. netselect uses icmp to determine latency, and hop count between you and a mirror. It can take a list of many mirrors, tests them, and reports which one has the best (lowest) metric. If you want rsync or ftp as a preferred transport, you could change it to only look for one of those. Throw in a few verbose flags to get more output.

# netselect -s 20 `wget https://launchpad.net/ubuntu/+archivemirrors -q -O - | grep '>http' |cut -d / -f 3 | tr '\n' ' '`
    3 mirror.tcpdiag.net
   14 149.20.4.71
   17 nz.archive.ubuntu.com
   17 ftp.citylink.co.nz
   17 mirrors.easynews.com
   18 mirrors.nl.eu.kernel.org
   18 ubuntu.securedservers.com
   45 mirrors.cat.pdx.edu
   58 mirror.peer1.net
   67 mirror.pnl.gov
   77 76.73.4.58
   90 ubuntu.mirrors.tds.net
   95 mirror.steadfast.net
  100 ubuntu-archives.mirror.nexicom.net
  102 mirrors.gigenet.com
  105 mirrors.xmission.com
  109 ubuntu.mirror.constant.com
  115 mirror.cs.umn.edu
  117 ubuntu.bhs.mirrors.ovh.net
  120 mirrors.rit.edu

In this case it looks like mirror.tcpdiag.net is the best choice.

# ping -c 3 mirror.tcpdiag.net
PING mirror.tcpdiag.net (69.160.243.150) 56(84) bytes of data.
64 bytes from ip-69-160-243-150.static.atlanticmetro.net (69.160.243.150): icmp_req=1 ttl=59 time=3.11 ms
64 bytes from ip-69-160-243-150.static.atlanticmetro.net (69.160.243.150): icmp_req=2 ttl=59 time=2.85 ms
64 bytes from ip-69-160-243-150.static.atlanticmetro.net (69.160.243.150): icmp_req=3 ttl=59 time=3.27 ms

--- mirror.tcpdiag.net ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 2.852/3.081/3.275/0.185 ms

3ms is pretty close.

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