Saturday, July 28, 2007

Finding out all processes associated with open sockets

Normally I've only used the 'netstat' command to find out what are the sockets opened in the operating system by using '-a' flag, but the new thing I've discovered recently is that netstat even allows me to track the processes that are opening them, via the '-p' flag. A simple dump of the command on my system gives the following output:
# netstat -ap       
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 *:http *:* LISTEN 6695/apache2
tcp 0 0 *:ssh *:* LISTEN 6604/sshd
udp 0 0 *:bootpc *:* 5294/dhcpcd
Active UNIX domain sockets (servers and established)
Proto RefCnt Flags Type State I-Node PID/Program name Path
unix 2 [ ACC ] STREAM LISTENING 10287 6696/apache2 /var/run/cgisock
unix 2 [ ACC ] STREAM LISTENING 9767 6324/gdm /tmp/.gdm_socket

... remaining output truncated.
The '-p' flag allows us to track applications that are holding onto open sockets, which is a good way to understand why certain sockets may have to be open, like bootpc in my example, which is necessary for the DHCP daemon to function.

Knowing this information will allow you to close down any unnecessary services that you do not need, reducing the amount of attack vectors that your machine is exposed to.

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