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I’m running a Debian Squeeze web server. I’ve installed memcached on it, and configured memcached to listen on a Unix domain socket (at /tmp/memcached.sock), as it only needs to receive messages from the website, which lives on the same server.

It seems to be working fine, but I’d also like to communicate with memcached via the shell, to check that it’s doing what I think it’s doing.

memcached accepts messages via a simple ASCII protocol (if I understand correctly). If it was listening on TCP/IP, I could send messages to it via e.g. nc:

$ echo "stats settings" | nc localhost 11211

But I can’t figure out how to send that text to the domain socket instead.

On my laptop (which runs OS X Lion), both nc and telnet have options (-U and -u respectively) to use domain sockets. However, on my Debian Squeeze web server, these options aren’t present.

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up vote 15 down vote accepted

With netcat-openbsd, there is a -U option. If you don't have it, you probably have netcat-traditional installed instead; I'd suggest switching.

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With socat (a 'bidirectional data relay between two data channels') you can can connect to the unix domain socket like this:

$ socat - UNIX-CONNECT:/tmp/memcached.sock
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You can use socat on Debian. To install it:

# apt-get install socat
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That looks pretty good. I don’t appear to have socat installed on my server, but it’s certainly available: packages.debian.org/squeeze/socat – Paul D. Waite Dec 13 '11 at 22:30

netcat-openbsd supports connecting to UNIX-domain sockets. Using this you can connect to either a UNIX-domain stream socket or a UNIX-domain datagram socket, and therefore you have to tell the socket's type to netcat.

for example, /dev/log file in Linux is a UNIX-domain datagram socket socket, thus nc -U /dev/log won't work. Instead use nc -uU /dev/log. Using -u along with -U tells netcat that it is a UNIX-domain datagram socket.

nc -U /tmp/socket  #Connect to UNIX-domain stream socket
nc -uU /tmp/socket #Connect to UNIX-domain datagram socket

Similarly, while using socat, use UNIX-CLIENT option. Using this option you can connect to both UNIX-domain stream and UNIX-domain datagram sockets. From its man page (man socat), "It first tries to connect and, if that fails, assumes it is a datagram socket, thus supporting both types".

socat - UNIX-CLIENT:/dev/socket #connect to UNIX-domain socket, irrespective of its type
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