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Keep an Eye on Your Linux Systems with Netstat |
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Source: enterprisenetworkingplanet.com - Posted by Vincenzo Ciaglia
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Two of the fundamental aspects of Linux system security and troubleshooting are knowing what services are running, and what connections and services are available. We're all familiar with ps for viewing active services. netstat goes a couple of steps further, and displays all available connections, services, and their status. . . .
Two of the fundamental aspects of Linux system security and troubleshooting are knowing what services are running, and what connections and services are available. We're all familiar with ps for viewing active services. netstat goes a couple of steps further, and displays all available connections, services, and their status. It shows one type of service that ps does not: services run from inetd or xinetd, because inetd/xinetd start them up on demand. If the service is available but not active, such as telnet, all you see in ps is either inetd or xinetd:
$ ps ax | grep -E 'telnet|inetd'
520 ? Ss 0:00 /usr/sbin/inetd
But netstat shows telnet sitting idly, waiting for a connection:
$ netstat --inet -a | grep telnet
tcp 0 0 *:telnet *:* LISTEN
This netstat invocation shows all activity:
$ netstat -a
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 *:telnet *:* LISTEN
tcp 0 0 *:ipp *:* LISTEN
tcp 0 0 *:smtp *:* LISTEN
tcp 0 0 192.168.1.5:32851 nest.anthill.echid:ircd
ESTABLISHED
udp 0 0 *:ipp *:*
Active UNIX domain sockets (servers and established)
Proto RefCnt Flags Type State I-Node Path
unix 2 [ ACC ] STREAM LISTENING 1065 /tmp/ksocket-carla/klaunchertDCh2b.slave-socket
unix 2 [ ACC ] STREAM LISTENING 1002 /tmp/ssh-OoMGfFm666/agent.666
unix 2 [ ACC ] STREAM LISTENING 819 private/smtp
Your total output will probably run to a couple hundred lines. (A fun and quick way to count lines of output is netstat -a | wc -l.) You can ignore everything under "Active UNIX domain sockets." Those are local inter-process communications, not network connections. To avoid displaying them at all, do this:
Read this full article at enterprisenetworkingplanet.com
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