What's this?

commandlinefu.com is the place to record those command-line gems that you return to again and again.

Delete that bloated snippets file you've been using and share your personal repository with the world. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.

If you have a new feature suggestion or find a bug, please get in touch via http://commandlinefu.uservoice.com/

Get involved!

You can sign-in using OpenID credentials, or register a traditional username and password.

First-time OpenID users will be automatically assigned a username which can be changed after signing in.

Universal configuration monitoring and system of record for IT.

Stay in the loop…

Follow the Tweets.

Every new command is wrapped in a tweet and posted to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning, there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.

» http://twitter.com/commandlinefu
» http://twitter.com/commandlinefu3
» http://twitter.com/commandlinefu10

Subscribe to the feeds.

Use your favourite RSS aggregator to stay in touch with the latest commands. There are feeds mirroring the 3 Twitter streams as well as for virtually every other subset (users, tags, functions,…):

Subscribe to the feed for:



May 19, 2015 - A Look At The New Commandlinefu
I've put together a short writeup on what kind of newness you can expect from the next iteration of clfu. Check it out here.
March 2, 2015 - New Management
I'm Jon, I'll be maintaining and improving clfu. Thanks to David for building such a great resource!

Top Tags





Commands tagged icmp from sorted by
Terminal - Commands tagged icmp - 5 results
echo foo | ncat [ip address] [port]
2012-10-26 10:53:47
User: dragonauta
Functions: echo

you can use a pair of commands to test firewalls.

1st launch this command at destination machine

ncat -l [-u] [port] | cat

then use this command at source machine to test remote port

echo foo | ncat [-u] [ip address] [port]

First command will listen at specified port.

It will listen TCP. If you use -u option will listen UDP.

Second command will send "foo" through ncat and will reach defined IP and port.

nmap -sT -PN -vv <target ip>
2011-07-22 02:37:19
User: Richie086

Change the IP address from to the target machines ip address. Even if the target has ICMP (ping) blocked, it will show you what ports are open on the target. Very handy for situations where you know the target is up and online but wont respond to pings.

sudo -s "echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_all"
2010-06-22 19:16:43
User: sliceoflinux
Functions: sudo
Tags: ping icmp

It really disables all ICMP responses not only the ping one.

If you want to enable it you can use:

sudo -s "echo 0 > /proc/sys/net/ipv4/icmp_echo_ignore_all"
echo foo | netcat 25
2009-09-13 01:33:02
User: pykler
Functions: echo

Using netcat, usuallly installed on debian/ubuntu.

Also to test against a sample server the following two commands may help

echo got milk? | netcat -l -p 25

python -c "import SocketServer; SocketServer.BaseRequestHandler.handle = lambda self: self.request.send('got milk?\n'); SocketServer.TCPServer(('', 25), SocketServer.BaseRequestHandler).serve_forever()"

echo "foo" > /dev/tcp/
2009-09-12 16:48:05
User: mobidyc
Functions: echo

this command will send a message to the socket 25 on host in tcp.

works on udp and icmp

understand only IP address, not hostname.

on the other side (, you can listen to this socket and test if you receive the message.

easy to diagnose a firewall problem or not.