I am configuring a pgpool instance to get a HA of postgresql services. I am following this configuration.

I found a command and I ran it manually in my console:

arping_cmd = 'arping -U $_IP_$ -w 1'

But it doesn't work, then I want to find a similar behaviour because I am on ubuntu 12.04. How can I do that ?

The $_IP_$ variable is replaced by the ip value in the configuration. The main problem is the arping command.

  • Welcome to askubuntu. Why do you think it didn't work? did you get an error of some kind? by using -U you are guaranteeing you won't get a response. (source man arping)
    – Elder Geek
    Commented Sep 30, 2014 at 15:52

3 Answers 3


When running the arping command in the terminal, I get the following output:

$ arping -U -w -1
arping: device (option -I) is required.
Usage: arping [-fqbDUAV] [-c count] [-w timeout] [-I device] [-s source] destination
  -f : quit on first reply
  -q : be quiet
  -b : keep broadcasting, don't go unicast
  -D : duplicate address detection mode
  -U : Unsolicited ARP mode, update your neighbours
  -A : ARP answer mode, update your neighbours
  -V : print version and exit
  -c count : how many packets to send
  -w timeout : how long to wait for a reply
  -I device : which ethernet device to use
  -s source : source ip address
  destination : ask for what ip address

The solution is in the first line after running the command. Use -I and -s to fix your problem. -I specifies the interface to do the arping on and -s is to specify the source your are doing the arping from. It's crappy, I know, but update your command to look like the below:

arping_cmd = 'arping -U $_IP_$ -w 1 -I ethX -s SOURCE_IP'

where ethx is your ethernet and SOURCE_IP is the IP you are going to do the arping from.

Hope this helps, Cheers


I had a similar problem on Fedora:

$ arping
arping: Suitable device could not be determined. Please, use option -I.

My solution was:

$ arping $ip_addr -I $(ip route get $ip_addr |  cut -d\  -f 3 |xargs)

Where ip_addr would contain the IP to be pinged.

To brake it down:

ip route get

would return the route and interface used by kernel for the specified ip: dev eth1  src

then use:

cut -d\  -f 3

to split the string by delimiter '\ ' (escaped space) and return 3-th substring:


then use xargs to remove all whitespaces around interface.

Hope it will be helpfull.


I get the same error as the submitter, saying that "-U" is not a valid option:

root@pgpool-2:/var/log# arping -U -w -1
arping: invalid option -- 'U'
ARPing 2.11, by Thomas Habets <[email protected]>
usage: arping [ -0aAbdDeFpqrRuv ] [ -w <us> ] [ -S <host/ip> ]
              [ -T <host/ip ] [ -s <MAC> ] [ -t <MAC> ] [ -c <count> ]
              [ -i <interface> ] <host/ip/MAC | -B>
For complete usage info, use --help or check the manpage.

I'm on Ubuntu 14.04 and there is no mention of "-U" in the manpage:

root@pgpool-2:/var/log# man arping | grep '\-U'

I changed mine to this:

arping_cmd = 'arping -v $_IP_$ -w 1 -c 100'

So basically:

  • -U doesn't exist, so remove it
  • Add -v to get verbose output, which may be helpful
  • Add -c 100 so that it eventually finishes... otherwise it runs forever

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