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Using the nstat network statistics command in Linux

Discover nstat, a tool for monitoring kernel SNMP and network interface stats and a part of the iproute2 package in Linux.
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nstat command overview

Photo by Lukas from Pexels

To continue the statistics theme of my writing over the last several weeks, I wanted to look at another powerful tool that we can use as Linux admins. You don't need to memorize every one of these tools. However, it is prudent to know each of the commands and have a basic understanding of them so you can choose the best command for your use case. Let's dive into nstat.

What is nstat?

The purpose of nstat is to pull network metrics from the kernel and display them to the user, focusing on SNMP.

Most command-line users are familiar with the netstat command from the net-tools package. The net-tools package was almost entirely deprecated in favor of the ip command suite, and you may have guessed that nstat belongs to the new package. 

Although netstat has a more user-friendly output, the nstat command holds its own and even has a few modern tricks up its sleeve.

Syntax

The command syntax is as follows:

nstat [OPTION] [ PATTERN [ PATTERN ] ]

You can view syntax information as well as options by running the -h help option. 

nstat -h

or

nstat --help

Now that we have the basic syntax down let's take a look at the output of the command.

Breakdown of output

When running nstat with no additional options, you get the following results:

[tcarrigan@rhel ~]$ nstat
#kernel
IpInReceives                    12057              0.0
IpInAddrErrors                  1                  0.0
IpInDelivers                    12000              0.0
IpOutRequests                   11060              0.0
IpOutNoRoutes                   252                0.0
TcpActiveOpens                  36                 0.0
TcpEstabResets                  3                  0.0
TcpInSegs                       11804              0.0
TcpOutSegs                      10960              0.0
TcpRetransSegs                  3                  0.0
TcpOutRsts                      29                 0.0
UdpInDatagrams                  196                0.0
UdpOutDatagrams                 246                0.0
Ip6InReceives                   18                 0.0
Ip6OutRequests                  31                 0.0
Ip6OutNoRoutes                  248                0.0
Ip6InMcastPkts                  18                 0.0
Ip6OutMcastPkts                 31                 0.0
Ip6InOctets                     1715               0.0
Ip6OutOctets                    2791               0.0
Ip6InMcastOctets                1715               0.0
Ip6OutMcastOctets               2791               0.0
Ip6InNoECTPkts                  18                 0.0
Icmp6OutMsgs                    13                 0.0
Icmp6OutRouterSolicits          3                  0.0
Icmp6OutNeighborSolicits        2                  0.0
Icmp6OutMLDv2Reports            8                  0.0
Icmp6OutType133                 3                  0.0
Icmp6OutType135                 2                  0.0
Icmp6OutType143                 8                  0.0
Udp6OutDatagrams                18                 0.0
TcpExtTW                        19                 0.0
TcpExtDelayedACKs               37                 0.0
TcpExtTCPHPHits                 10981              0.0
TcpExtTCPPureAcks               142                0.0
TcpExtTCPHPAcks                 267                0.0
TcpExtTCPLossUndo               3                  0.0
TcpExtTCPTimeouts               3                  0.0
TcpExtTCPAbortOnClose           3                  0.0
TcpExtTCPRcvCoalesce            327                0.0
TcpExtTCPAutoCorking            5                  0.0
TcpExtTCPSynRetrans             3                  0.0
TcpExtTCPOrigDataSent           390                0.0
TcpExtTCPHystartTrainDetect     1                  0.0
TcpExtTCPHystartTrainCwnd       17                 0.0
TcpExtTCPWinProbe               1                  0.0
TcpExtTCPDelivered              424                0.0
IpExtInMcastPkts                41                 0.0
IpExtOutMcastPkts               47                 0.0
IpExtInOctets                   54131913           0.0
IpExtOutOctets                  829632             0.0
IpExtInMcastOctets              3902               0.0
IpExtOutMcastOctets             4142               0.0
IpExtInNoECTPkts                48401              0.0

Notice that while this is a longer output, almost all of this information is useful, given the right circumstance. You can use a variety of options to change the output to include or exclude specific fields as well as change the formatting of the output altogether.

As much of this output is RAW, it can be difficult to understand these values and what they mean to you. I found this resource on the web that does a great job of explaining the various data fields. . 

Options to know

-a, --ignore - Dump absolute values of counters. (The default calculates the increments since the previous run)

[tcarrigan@rhel ~]$ nstat -a
#kernel
IpInReceives                    12064              0.0
IpInAddrErrors                  1                  0.0
IpInDelivers                    12007              0.0
IpOutRequests                   11069              0.0
IpOutNoRoutes                   252                0.0
TcpActiveOpens                  36                 0.0
TcpEstabResets                  3                  0.0
TcpInSegs                       11804              0.0
TcpOutSegs                      10960              0.0
TcpRetransSegs                  3                  0.0
TcpOutRsts                      29                 0.0
UdpInDatagrams                  203                0.0
UdpOutDatagrams                 255                0.0
Ip6InReceives                   18                 0.0
Ip6OutRequests                  31                 0.0
Ip6OutNoRoutes                  248                0.0
Ip6InMcastPkts                  18                 0.0
Ip6OutMcastPkts                 31                 0.0
Ip6InOctets                     1715               0.0
Ip6OutOctets                    2791               0.0
Ip6InMcastOctets                1715               0.0
Ip6OutMcastOctets               2791               0.0
Ip6InNoECTPkts                  18                 0.0
Icmp6OutMsgs                    13                 0.0
Icmp6OutRouterSolicits          3                  0.0
Icmp6OutNeighborSolicits        2                  0.0
Icmp6OutMLDv2Reports            8                  0.0
Icmp6OutType133                 3                  0.0
Icmp6OutType135                 2                  0.0
Icmp6OutType143                 8                  0.0
Udp6OutDatagrams                18                 0.0
TcpExtTW                        19                 0.0
TcpExtDelayedACKs               37                 0.0
TcpExtTCPHPHits                 10981              0.0
TcpExtTCPPureAcks               142                0.0
TcpExtTCPHPAcks                 267                0.0
TcpExtTCPLossUndo               3                  0.0
TcpExtTCPTimeouts               3                  0.0
TcpExtTCPAbortOnClose           3                  0.0
TcpExtTCPRcvCoalesce            327                0.0
TcpExtTCPAutoCorking            5                  0.0
TcpExtTCPSynRetrans             3                  0.0
TcpExtTCPOrigDataSent           390                0.0
TcpExtTCPHystartTrainDetect     1                  0.0
TcpExtTCPHystartTrainCwnd       17                 0.0
TcpExtTCPWinProbe               1                  0.0
TcpExtTCPDelivered              424                0.0
IpExtInMcastPkts                41                 0.0
IpExtOutMcastPkts               47                 0.0
IpExtInOctets                   54132445           0.0
IpExtOutOctets                  830316             0.0
IpExtInMcastOctets              3902               0.0
IpExtOutMcastOctets             4142               0.0
IpExtInNoECTPkts                48408              0.0

-z, --zeroes - Dumps all zeroes counters. These are ignored by default.

*Note this output is shortened for display*

[tcarrigan@rhel ~]$ nstat -z
#kernel
IpInReceives                    4                  0.0
IpInHdrErrors                   0                  0.0
IpInAddrErrors                  0                  0.0
IpForwDatagrams                 0                  0.0
IpInUnknownProtos               0                  0.0
IpInDiscards                    0                  0.0
IpInDelivers                    4                  0.0
IpOutRequests                   4                  0.0
IpOutDiscards                   0                  0.0
IpOutNoRoutes                   0                  0.0
IpReasmTimeout                  0                  0.0
IpReasmReqds                    0                  0.0
IpReasmOKs                      0                  0.0
IpReasmFails                    0                  0.0
IpFragOKs                       0                  0.0
IpFragFails                     0                  0.0
IpFragCreates                   0                  0.0

-r, --reset - Resets the history, thus excluding averages since the last run.

[tcarrigan@rhel ~]$ nstat -r
#kernel
IpInReceives                    12069              0.0
IpInAddrErrors                  1                  0.0
IpInDelivers                    12012              0.0
IpOutRequests                   11074              0.0
IpOutNoRoutes                   252                0.0
TcpActiveOpens                  36                 0.0
TcpEstabResets                  3                  0.0
TcpInSegs                       11804              0.0
TcpOutSegs                      10960              0.0
TcpRetransSegs                  3                  0.0
TcpOutRsts                      29                 0.0
UdpInDatagrams                  208                0.0
UdpOutDatagrams                 260                0.0
Ip6InReceives                   18                 0.0
Ip6OutRequests                  31                 0.0
Ip6OutNoRoutes                  248                0.0
Ip6InMcastPkts                  18                 0.0
Ip6OutMcastPkts                 31                 0.0
Ip6InOctets                     1715               0.0
Ip6OutOctets                    2791               0.0
Ip6InMcastOctets                1715               0.0
Ip6OutMcastOctets               2791               0.0
Ip6InNoECTPkts                  18                 0.0
Icmp6OutMsgs                    13                 0.0
Icmp6OutRouterSolicits          3                  0.0
Icmp6OutNeighborSolicits        2                  0.0
Icmp6OutMLDv2Reports            8                  0.0
Icmp6OutType133                 3                  0.0
Icmp6OutType135                 2                  0.0
Icmp6OutType143                 8                  0.0
Udp6OutDatagrams                18                 0.0
TcpExtTW                        19                 0.0
TcpExtDelayedACKs               37                 0.0
TcpExtTCPHPHits                 10981              0.0
TcpExtTCPPureAcks               142                0.0
TcpExtTCPHPAcks                 267                0.0
TcpExtTCPLossUndo               3                  0.0
TcpExtTCPTimeouts               3                  0.0
TcpExtTCPAbortOnClose           3                  0.0
TcpExtTCPRcvCoalesce            327                0.0
TcpExtTCPAutoCorking            5                  0.0
TcpExtTCPSynRetrans             3                  0.0
TcpExtTCPOrigDataSent           390                0.0
TcpExtTCPHystartTrainDetect     1                  0.0
TcpExtTCPHystartTrainCwnd       17                 0.0
TcpExtTCPWinProbe               1                  0.0
TcpExtTCPDelivered              424                0.0
IpExtInMcastPkts                41                 0.0
IpExtOutMcastPkts               47                 0.0
IpExtInOctets                   54132825           0.0
IpExtOutOctets                  830696             0.0
IpExtInMcastOctets              3902               0.0
IpExtOutMcastOctets             4142               0.0
IpExtInNoECTPkts                48413              0.0

You can also use the following options to change the time intervals for reports: 

-d, --scan x - Run in daemon mode to collect statistics. x is an interval between measurements in seconds.

-t, --interval x : Where x is the interval to average rates. The default value is 60 seconds.

For more options, check out the man page for this command: man nstat

Wrap up

To summarize, we looked at the overall purpose of the nstat command. Knowing where we came from, with netstat, allows us to appreciate nstat and its goal of providing more useful data. We looked at the syntax of the command, as well as some of the various options that can be utilized. If more information is needed, be sure to check the man pages or your favorite search engine. If you have another command that you would like to see covered, send an email to the team at enable-sysadmin@redhat.com!

[ Want more for your network? Download a free ebook on network automation with Ansible. ]

Topics:   Networking  
Author’s photo

Tyler Carrigan

Tyler is a community manager at Enable Sysadmin, a submarine veteran, and an all-round tech enthusiast! He was first introduced to Red Hat in 2012 by way of a Red Hat Enterprise Linux-based combat system inside the USS Georgia Missile Control Center. More about me

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