When we want to check whether a host is reachable (at all), we can use the ping command:
It sends ICMP Echo Requests to the given host and reports how many packages are received and responded to. The option -c can be used to set how many requests are sent.
Checking specific endpoints
A disadvantage of ping is that we cannot configure a specific endpoint (= host + port) to ping. More advanced tools offer alternatives. The following command pings the FTP port of www.roland-kluge.de:
nping -p 21 www.roland-kluge.de
nping belongs to the nmap package. On Ubuntu, nmap can be installed as follows: sudo apt-get install nmap .
Another tool is Netcat. The advantage of nc is that the error code indicates whether the endpoint was pinged successfully, making it useful for checking endpoint availability in scripts.
nc -w 1 www.roland-kluge.de 21 echo $? # returns 0 nc -w 1 www.roland-kluge.de 1 echo $? # returns 1
On Ubuntu, Netcat can be installed as follows: sudo apt-get install netcat .