Linux distributions grow, get updated, and more advanced. Most tools that you have grown accustomed to using remain, But a few have been replaced. Many reasons for the replacement of core tools. Most of these tools are removed because they are inefficient and replaced with better alternatives. Old networking tools like netstat and ifconfig work by accessing files in the /proc filesystem to aggregate their response. This behavior has been fine for years, especially on smaller systems. As systems grow and complexity increases the chances for inaccurate responses have increased. So what is the replacement for netstat?
The Linux networking subsystem has continued to evolve with the changing of the Linux Kernel, which has lead to new networking functions and processes. The new tools leverage Netlink Sockets to provide their information, which are much more efficient. For a full writeup on the reasons for the switch over I recommend this article on the real reasons of the Linux replacement for netstat.
Netstat is my goto tool for getting a list of open ports on a system and associated processes. Even with the changes in the works I have loaded the program from the net-tools package, until I couldn’t. Recently I was helping a client with a OpenSuse 15 system that didn’t have netstat, and it could not locate the package when I attempted to install it. I then tried the alternative to netstat, ss.
SS is the replacement for netstat
SS stands for “Socket Statistics” and operates in a manner similar to netstat. It formats things differently, leading to some required adjustments. Here is the basic help output for the ss command.
SS Usage
bdoga@webserver:~$ ss --help
Usage: ss [ OPTIONS ]
ss [ OPTIONS ] [ FILTER ]
-h, --help this message
-V, --version output version information
-n, --numeric don't resolve service names
-r, --resolve resolve host names
-a, --all display all sockets
-l, --listening display listening sockets
-o, --options show timer information
-e, --extended show detailed socket information
-m, --memory show socket memory usage
-p, --processes show process using socket
-i, --info show internal TCP information
-s, --summary show socket usage summary
-b, --bpf show bpf filter socket information
-E, --events continually display sockets as they are destroyed
-Z, --context display process SELinux security contexts
-z, --contexts display process and socket SELinux security contexts
-N, --net switch to the specified network namespace name
-4, --ipv4 display only IP version 4 sockets
-6, --ipv6 display only IP version 6 sockets
-0, --packet display PACKET sockets
-t, --tcp display only TCP sockets
-u, --udp display only UDP sockets
-d, --dccp display only DCCP sockets
-w, --raw display only RAW sockets
-x, --unix display only Unix domain sockets
-f, --family=FAMILY display sockets of type FAMILY
-A, --query=QUERY, --socket=QUERY
QUERY := {all|inet|tcp|udp|raw|unix|unix_dgram|unix_stream|unix_seqpacket|packet|netlink}[,QUERY]
-D, --diag=FILE Dump raw information about TCP sockets to FILE
-F, --filter=FILE read filter information from FILE
FILTER := [ state STATE-FILTER ] [ EXPRESSION ]
STATE-FILTER := {all|connected|synchronized|bucket|big|TCP-STATES}
TCP-STATES := {established|syn-sent|syn-recv|fin-wait-{1,2}|time-wait|closed|close-wait|last-ack|listen|closing}
connected := {established|syn-sent|syn-recv|fin-wait-{1,2}|time-wait|close-wait|last-ack|closing}
synchronized := {established|syn-recv|fin-wait-{1,2}|time-wait|close-wait|last-ack|closing}
bucket := {syn-recv|time-wait}
big := {established|syn-sent|fin-wait-{1,2}|closed|close-wait|last-ack|listen|closing}
So while it may not be netstat it appears to be a very robust tool. Ss allows the querying of specific information and then filter the results directly. It is useful to filter directly without relying on a tool like grep or awk. But there is nothing to stop you from piping the output into the tool of your choice.
SS Usage Examples
bdoga@webserver:~$ ss -lt State Recv-Q Send-Q Local Address:Port Peer Address:Port LISTEN 0 128 *:7080 *:* LISTEN 0 128 *:6032 *:* LISTEN 0 128 *:http *:* LISTEN 0 128 *:6033 *:* LISTEN 0 128 *:6033 *:* LISTEN 0 128 *:6033 *:* LISTEN 0 128 *:6033 *:* LISTEN 0 128 *:ssh *:* LISTEN 0 128 *:https *:* LISTEN 0 128 :::ssh :::*
Show all the tcp ports “-t” that the server is listening “-l” to.
bdoga@webserver:~$ sudo ss -ltp
State Recv-Q Send-Q Local Address:Port Peer Address:Port
LISTEN 0 128 *:7080 *:* users:(("litespeed",pid=21324,fd=11),("litespeed",pid=21321,fd=11))
LISTEN 0 128 *:6032 *:* users:(("proxysql_galera",pid=28271,fd=28),("proxysql",pid=3649,fd=28))
LISTEN 0 128 *:http *:* users:(("litespeed",pid=21324,fd=9),("litespeed",pid=21321,fd=9))
LISTEN 0 128 *:6033 *:* users:(("proxysql_galera",pid=28271,fd=22),("proxysql",pid=3649,fd=22))
LISTEN 0 128 *:6033 *:* users:(("proxysql_galera",pid=28271,fd=21),("proxysql",pid=3649,fd=21))
LISTEN 0 128 *:6033 *:* users:(("proxysql_galera",pid=28271,fd=20),("proxysql",pid=3649,fd=20))
LISTEN 0 128 *:6033 *:* users:(("proxysql_galera",pid=28271,fd=19),("proxysql",pid=3649,fd=19))
LISTEN 0 128 *:ssh *:* users:(("sshd",pid=950,fd=3))
LISTEN 0 128 *:https *:* users:(("litespeed",pid=21324,fd=10),("litespeed",pid=21321,fd=10))
LISTEN 0 128 :::ssh :::* users:(("sshd",pid=950,fd=4))
Show all the tcp ports “-t” that the server is listening “-l” on. What process “-p” are using those ports. The “-p” flag requires root/sudo access to properly display which processes are using those ports.
bdoga@webserver:~$ sudo ss -lup
State Recv-Q Send-Q Local Address:Port Peer Address:Port
UNCONN 0 0 *:59879 *:* users:(("rsyslogd",pid=556,fd=5))
UNCONN 0 0 192.168.28.34:ntp *:* users:(("ntpd",pid=9421,fd=21))
UNCONN 0 0 10.10.10.28:ntp *:* users:(("ntpd",pid=9421,fd=20))
UNCONN 0 0 209.33.221.34:ntp *:* users:(("ntpd",pid=9421,fd=19))
UNCONN 0 0 127.0.0.1:ntp *:* users:(("ntpd",pid=9421,fd=18))
UNCONN 0 0 *:ntp *:* users:(("ntpd",pid=9421,fd=17))
UNCONN 0 0 *:snmp *:* users:(("snmpd",pid=1045,fd=7))
UNCONN 0 0 *:https *:* users:(("litespeed",pid=21324,fd=18),("litespeed",pid=21321,fd=18))
UNCONN 0 0 127.0.0.1:8822 *:* users:(("Site24x7Agent",pid=1141,fd=19))
UNCONN 0 0 fe80::218:3eff:fe57:7bf2%eth1:ntp :::* users:(("ntpd",pid=9421,fd=24))
UNCONN 0 0 fe80::216:3cff:fe4e:8673%eth0:ntp :::* users:(("ntpd",pid=9421,fd=23))
UNCONN 0 0 ::1:ntp :::* users:(("ntpd",pid=9421,fd=22))
UNCONN 0 0 :::ntp :::* users:(("ntpd",pid=9421,fd=16))
Same as the previous example but listing udp ports “-u”.
bdoga@webserver:~$ sudo ss -at4p
State Recv-Q Send-Q Local Address:Port Peer Address:Port
LISTEN 0 128 *:7080 *:* users:(("litespeed",pid=21324,fd=11),("litespeed",pid=21321,fd=11))
LISTEN 0 128 *:6032 *:* users:(("mysql",pid=28336,fd=28),("timeout",pid=28335,fd=28),("proxysql_galera",pid=28333,fd=28),("proxysql_galera",pid=28332,fd=28),("proxysql_galera",pid=27839,fd=28),("proxysql",pid=3649,fd=28))
LISTEN 0 128 *:http *:* users:(("litespeed",pid=21324,fd=9),("litespeed",pid=21321,fd=9))
LISTEN 0 128 *:6033 *:* users:(("mysql",pid=28336,fd=22),("timeout",pid=28335,fd=22),("proxysql_galera",pid=28333,fd=22),("proxysql_galera",pid=28332,fd=22),("proxysql_galera",pid=27839,fd=22),("proxysql",pid=3649,fd=22))
LISTEN 0 128 *:6033 *:* users:(("mysql",pid=28336,fd=21),("timeout",pid=28335,fd=21),("proxysql_galera",pid=28333,fd=21),("proxysql_galera",pid=28332,fd=21),("proxysql_galera",pid=27839,fd=21),("proxysql",pid=3649,fd=21))
LISTEN 0 128 *:6033 *:* users:(("mysql",pid=28336,fd=20),("timeout",pid=28335,fd=20),("proxysql_galera",pid=28333,fd=20),("proxysql_galera",pid=28332,fd=20),("proxysql_galera",pid=27839,fd=20),("proxysql",pid=3649,fd=20))
LISTEN 0 128 *:6033 *:* users:(("mysql",pid=28336,fd=19),("timeout",pid=28335,fd=19),("proxysql_galera",pid=28333,fd=19),("proxysql_galera",pid=28332,fd=19),("proxysql_galera",pid=27839,fd=19),("proxysql",pid=3649,fd=19))
LISTEN 0 128 *:ssh *:* users:(("sshd",pid=950,fd=3))
LISTEN 0 128 *:https *:* users:(("litespeed",pid=21324,fd=10),("litespeed",pid=21321,fd=10))
TIME-WAIT 0 0 209.33.221.34:58184 209.33.221.83:mysql
TIME-WAIT 0 0 127.0.0.1:34804 127.0.0.1:6032
TIME-WAIT 0 0 127.0.0.1:34470 127.0.0.1:6032
TIME-WAIT 0 0 209.33.221.34:45368 209.33.221.36:mysql
ESTAB 0 0 209.33.221.34:37194 209.33.221.67:mysql users:(("mysql",pid=28336,fd=109),("timeout",pid=28335,fd=109),("proxysql_galera",pid=28333,fd=109),("proxysql_galera",pid=28332,fd=109),("proxysql_galera",pid=27839,fd=109),("proxysql",pid=3649,fd=109))
TIME-WAIT 0 0 127.0.0.1:33812 127.0.0.1:6032
To show all “-a” tcp “-t” but only IPv4 “-4” interfaces and their associated processes “-p”.
I will take a little while to fully make the switch since I have used netstat for decades. Although it appears the future is bright, and ss should be able to take care of me in the future. Hopefully this overview helps you make the switch as well.
Here are some of the resources that I used when researching this topic:
Want to learn how to Force Disconnect iscsi and Reconnect iscsi on centos6+, check out this post to find out how.