Manpage of ss says:

FILTER := [ state TCP-STATE ] [ EXPRESSION ]
Please take a look at the official documentation (Debian package iproute-doc) for details regarding filters.

What does that mean? I can’t find anything under /usr/share/doc/iproute2-doc/.

$ ls /usr/share/doc/iproute2-doc/ss.html
ls: cannot access '/usr/share/doc/iproute2-doc/ss.html': No such file or directory

$ ls /usr/share/doc/iproute2-doc/
actions  changelog.Debian.gz  copyright  examples  README  README.decnet  README.devel  README.distribution.gz  README.iproute2+tc  README.lnstat

Is the document also online somewhere for browsing?

Thanks.

Contents hide

Answers:

Method 1

Method 2

Method 3

Method 4

SS Utility: Quick Intro

Alexey Kuznetosv, [email protected]

1. Why?

2. Old news

3. Time to talk about new functionality.

3.1 Filtering by state.

3.2 Filtering by addresses and ports.

4. Examples

5. Returning to ground: real manual

5.1 Command arguments

OPTIONS

STATE-FILTER

ADDRESS_FILTER

5.2 Environment variables

5.3 Output format

6. Some numbers

Answers:

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Method 1

The documentation is available in the Debian 9 package but was removed in later releases because it was outdated. The manpage is supposed to be the complete documentation now. (But it doesn’t have much to say about the details of filters.)

Method 2

       FILTER := [ state STATE-FILTER ] [ EXPRESSION ]
              Please take a look at the official documentation for details regarding filters.

STATE-FILTER
       STATE-FILTER allows to construct arbitrary set of states to match. Its syntax is sequence of keywords state and  exclude  fol‐
       lowed by identifier of state.

       Available identifiers are:

              All  standard TCP states: established, syn-sent, syn-recv, fin-wait-1, fin-wait-2, time-wait, closed, close-wait, last-
              ack, listening and closing.

              all - for all the states

              connected - all the states except for listening and closed

              synchronized - all the connected states except for syn-sent

              bucket - states, which are maintained as minisockets, i.e.  time-wait and syn-recv

              big - opposite to bucket
...

   ss -o state established '( dport = :ssh or sport = :ssh )'
          Display all established ssh connections.

   ss -o state fin-wait-1 '( sport = :http or sport = :https )' dst 193.233.7/24
          List all the tcp sockets in state FIN-WAIT-1 for our apache to network 193.233.7/24 and look at their timers.

ss [options] [ FILTER ]

can be expanded to

ss [options] [ state STATE-FILTER ] [ EXPRESSION ]

where options are

[-hVHnraloempiKsZNb460tudwxS] [-f FAMILY] [-A QUERY] [-D FILE] [-D FILE]

STATE-FILTER is one of

established, syn-sent, syn-recv, fin-wait-1, fin-wait-2, time-wait, closed, close-wait, last-ack, listening, closing, all, connected, synchronized, bucket, big

and we can deduce from the examples that EXPRESSION is a list of ip-rule SELECTORs.

SELECTOR := [ not ] [ from PREFIX ] [ to PREFIX ] [ tos TOS ] [ fwmark FWMARK[/MASK] ] [ iif STRING ] [ oif STRING ] [ pref NUMBER ] [ l3mdev ] [ uidrange NUMBER-NUMBER ] [ ipproto PROTOCOL ] [ sport [ NUMBER | NUMBER-NUMBER ] ] [ dport [ NUMBER | NUMBER-NUMBER ] ] [ tun_id TUN_ID ]

Method 3

I was wondering this same thing and the other answers and comments providing a link to the source was incredibly helpful.

The overall FILTER syntax is still a bit confusing, but based on an example from Linode showing how to check for ports above the secure (root required) range and the source I was able to put together a “complex” filter to check for opened ports in a specific range.

All three of these examples are functionally equivalent:

ss -a -t '( dport geq :5900 and dport leq :5999 or sport geq :5900 and sport leq :5999 )'

ss -a -t '( dport >= :5900 and dport <= :5999 or sport >= :5900 and sport <= :5999 )'

ss -a -t '( dport >= :5900 & dport <= :5999 | sport >= :5900 & sport <= :5999 )'

In this case the port(s) I’m hunting for are related to VNC, because the Vagrant and Packer tools from Hashicorp (and the virtualization tools they interact with like Virtualbox/VMware/libvirt) will automatically allocate ports in this range for virtual machines launched “headless” so that you can interact with the VM console without just sending in raw keystrokes.

The part that tripped me up for a second was that in the source code it has GEQ and LEQ but the actual filter syntax requires them to be lowercase or the symbolic representation >= or <=, while in the source code you can see the eq is defined as lowercase.

The other sneaky/confusing thing is that = and eq and == all work for equality.

Method 4

This may helps

https://www.apt-browse.org/browse/ubuntu/trusty/main/all/iproute2-doc/3.12.0-2/file/usr/share/doc/iproute2-doc/ss.html

SS Utility: Quick Intro

Alexey Kuznetosv, `[email protected]`

some_negative_number, 20 Sep 2001

ss is one another utility to investigate sockets.
Functionally it is NOT better than netstat combined
with some perl/awk scripts and though it is surely faster
it is not enough to make it much better. 🙂
So, stop reading this now and do not waste your time.
Well, certainly, it proposes some functionality, which current
netstat is still not able to do, but surely will soon.

1. Why?

/proc interface is inadequate, unfortunately.
When amount of sockets is enough large, netstat or even
plain cat /proc/net/tcp/ cause nothing but pains and curses.
In linux-2.4 the desease became worse: even if amount
of sockets is small reading /proc/net/tcp/ is slow enough.

This utility presents a new approach, which is supposed to scale
well. I am not going to describe technical details here and
will concentrate on description of the command.
The only important thing to say is that it is not so bad idea
to load module tcp_diag, which can be found in directory
Modules of iproute2. If you do not make this ss
will work, but it falls back to /proc and becomes slow
like netstat, well, a bit faster yet (see section “Some numbers”).

2. Old news

In the simplest form ss is equivalent to netstat
with some small deviations.

ss -t -a dumps all TCP sockets

ss -u -a dumps all UDP sockets

ss -w -a dumps all RAW sockets

ss -x -a dumps all UNIX sockets

Option -o shows TCP timers state.
Option -e shows some extended information.
Etc. etc. etc. Seems, all the options of netstat related to sockets
are supported. Though not AX.25 and other bizarres. 🙂
If someone wants, he can make support for decnet and ipx.
Some rudimentary support for them is already present in iproute2 libutils,
and I will be glad to see these new members.

However, standard functionality is a bit different:

The first: without option -a sockets in states
TIME-WAIT and SYN-RECV are skipped too.
It is more reasonable default, I think.

The second: format of UNIX sockets is different. It coincides
with tcp/udp. Though standard kernel still does not allow to
see write/read queues and peer address of connected UNIX sockets,
the patch doing this exists.

The third: default is to dump only TCP sockets, rather than all of the types.

The next: by default it does not resolve numeric host addresses (like ip)!
Resolving is enabled with option -r. Service names, usually stored
in local files, are resolved by default. Also, if service database
does not contain references to a port, ss queries system
rpcbind. RPC services are prefixed with rpc.
Resolution of services may be suppressed with option -n.

It does not accept “long” options (I dislike them, sorry).
So, address family is given with family identifier following
option -f to be algined to iproute2 conventions.
Mostly, it is to allow option parser to parse
addresses correctly, but as side effect it really limits dumping
to sockets supporting only given family. Option -A followed
by list of socket tables to dump is also supported.
Logically, id of socket table is different of _address_ family, which is
another point of incompatibility. So, id is one of
all, tcp, udp,
raw, inet, unix, packet, netlink. See?
Well, inet is just abbreviation for tcp|udp|raw
and it is not difficult to guess that packet allows
to look at packet sockets. Actually, there are also some other abbreviations,
f.e. unix_dgram selects only datagram UNIX sockets.

The next: well, I still do not know. 🙂

3. Time to talk about new functionality.

It is builtin filtering of socket lists.

3.1 Filtering by state.

ss allows to filter socket states, using keywords
state and exclude, followed by some state
identifier.

State identifier are standard TCP state names (not listed,
they are useless for you if you already do not know them)
or abbreviations:

all – for all the states

bucket – for TCP minisockets (TIME-WAIT|SYN-RECV)

big – all except for minisockets

connected – not closed and not listening

synchronized – connected and not SYN-SENT

F.e. to dump all tcp sockets except SYN-RECV:



   ss exclude SYN-RECV

If neither state nor exclude directives
are present,
state filter defaults to all with option -a
or to all,
excluding listening, syn-recv, time-wait and closed sockets.

3.2 Filtering by addresses and ports.

Option list may contain address/port filter.
It is boolean expression which consists of boolean operation
or, and, not and predicates.
Actually, all the flavors of names for boolean operations are eaten:
&, &&, |, ||, !, but do not forget
about special sense given to these symbols by unix shells and escape
them correctly, when used from command line.

Predicates may be of the folowing kinds:

A. Address/port match, where address is checked against mask
and port is either wildcard or exact. It is one of:
```
        dst prefix:port

        src prefix:port

        src unix:STRING

        src link:protocol:ifindex

        src nl:channel:pid
```
Both prefix and port may be absent or replaced with *,
which means wildcard. UNIX socket use more powerful scheme
matching to socket names by shell wildcards. Also, prefixes
unix: and link: may be omitted, if address family is evident
from context (with option -x or with -f unix
or with unix keyword)

F.e.
```
        dst 10.0.0.1

        dst 10.0.0.1:

        dst 10.0.0.1/32:

        dst 10.0.0.1:*
```
are equivalent and mean socket connected to
any port on host 10.0.0.1
```
        dst 10.0.0.0/24:22
```
sockets connected to port 22 on network
10.0.0.0…255.

Note that port separated of address with colon, which creates
troubles with IPv6 addresses. Generally, we interpret the last
colon as splitting port. To allow to give IPv6 addresses,
trick like used in IPv6 HTTP URLs may be used:
```
      dst [::1]
```
are sockets connected to ::1 on any port

Another way is dst ::1128/. / helps to understand that
colon is part of IPv6 address.

Now we can add another alias for dst 10.0.0.1:
dst [10.0.0.1]. 🙂

Address may be a DNS name. In this case all the addresses are looked
up (in all the address families, if it is not limited by option -f
or special address prefix inet:, inet6) and resulting
expression is or over all of them.

B. Port expressions:
```
      dport >= :1024

      dport != :22

      sport < :32000
```
etc.

All the relations: <, >, =, >=, =, ==,
!=, eq, ge, lt, ne…
Use variant which you like more, but not forget to escape special
characters when typing them in command line. 🙂

Note that port number syntactically coincides to the case A!
You may even add an IP address, but it will not participate
incomparison, except for == and !=, which are equivalent
to corresponding predicates of type A. F.e.

dst 10.0.0.1:22
is equivalent to dport eq 10.0.0.1:22
and
not dst 10.0.0.1:22 is equivalent to
dport neq 10.0.0.1:22

C. Keyword autobound. It matches to sockets bound automatically
on local system.

4. Examples

1. List all the tcp sockets in state FIN-WAIT-1 for our apache
to network 193.233.7/24 and look at their timers:
```
   ss -o state fin-wait-1 ( sport = :http or sport = :https ) 

                          dst 193.233.7/24
```
Oops, forgot to say that missing logical operation is
equivalent to and.

2. Well, now look at the rest…
```
   ss -o excl fin-wait-1

   ss state fin-wait-1 ( sport neq :http and sport neq :https ) 

                       or not dst 193.233.7/24
```
Note that we have to do two calls of ss to do this.
State match is always anded to address/port match.
The reason for this is purely technical: ss does fast skip of
not matching states before parsing addresses and I consider the
ability to skip fastly gobs of time-wait and syn-recv sockets
as more important than logical generality.

3. So, let’s look at all our sockets using autobound ports:
```
   ss -a -A all autobound
```

4. And eventually find all the local processes connected
to local X servers:
```
   ss -xp dst “/tmp/.X11-unix/*”
```
Pardon, this does not work with current kernel, patching is required.
But we still can look at server side:
```
   ss -x src “/tmp/.X11-unix/*”
```

5. Returning to ground: real manual

5.1 Command arguments

General format of arguments to ss is:



       ss [ OPTIONS ] [ STATE-FILTER ] [ ADDRESS-FILTER ]

`OPTIONS`

OPTIONS is list of single letter options, using common unix
conventions.

-h – show help page

-? – the same, of course

-v, -V – print version of ss and exit

-s – print summary statistics. This option does not parse
socket lists obtaining summary from various sources. It is useful
when amount of sockets is so huge that parsing /proc/net/tcp
is painful.

-D FILE – do not display anything, just dump raw information
about TCP sockets to FILE after applying filters. If FILE is –
stdout is used.

-F FILE – read continuation of filter from FILE.
Each line of FILE is interpreted like single command line option.
If FILE is – stdin is used.

-r – try to resolve numeric address/ports

-n – do not try to resolve ports

-o – show some optional information, f.e. TCP timers

-i – show some infomration specific to TCP (RTO, congestion
window, slow start threshould etc.)

-e – show even more optional information

-m – show extended information on memory used by the socket.
It is available only with tcp_diag enabled.

-p – show list of processes owning the socket

-f FAMILY – default address family used for parsing addresses.
Also this option limits listing to sockets supporting
given address family. Currently the following families
are supported: unix, inet, inet6, link,
netlink.

-4 – alias for -f inet

-6 – alias for -f inet6

-0 – alias for -f link

-A LIST-OF-TABLES – list of socket tables to dump, separated
by commas. The following identifiers are understood:
all, inet, tcp, udp, raw,
unix, packet, netlink, unix_dgram,
unix_stream, packet_raw, packet_dgram.

-x – alias for -A unix

-t – alias for -A tcp

-u – alias for -A udp

-w – alias for -A raw

-a – show sockets of all the states. By default sockets
in states LISTEN, TIME-WAIT, SYN_RECV
and CLOSE are skipped.

-l – show only sockets in state LISTEN

`STATE-FILTER`

STATE-FILTER allows to construct arbitrary set of
states to match. Its syntax is sequence of keywords state
and exclude followed by identifier of state.
Available identifiers are:

All standard TCP states: established, syn-sent,
syn-recv, fin-wait-1, fin-wait-2, time-wait,
closed, close-wait, last-ack, listen and closing.

all – for all the states

connected – all the states except for listen and closed

synchronized – all the connected states except for
syn-sent

bucket – states, which are maintained as minisockets, i.e.
time-wait and syn-recv.

big – opposite to bucket

`ADDRESS_FILTER`

ADDRESS_FILTER is boolean expression with operations and, or
and not, which can be abbreviated in C style f.e. as &,
&&.

Predicates check socket addresses, both local and remote.
There are the following kinds of predicates:

dst ADDRESS_PATTERN – matches remote address and port

src ADDRESS_PATTERN – matches local address and port

dport RELOP PORT – compares remote port to a number

sport RELOP PORT – compares local port to a number

autobound – checks that socket is bound to an ephemeral
port

RELOP is some of <=, >=, == etc.
To make this more convinient for use in unix shell, alphabetic
FORTRAN-like notations le, gt etc. are accepted as well.

The format and semantics of ADDRESS_PATTERN depends on address
family.

inet – ADDRESS_PATTERN consists of IP prefix, optionally
followed by colon and port. If prefix or port part is absent or replaced
with *, this means wildcard match.

inet6 – The same as inet, only prefix refers to an IPv6
address. Unlike inet colon becomes ambiguous, so that ss allows
to use scheme, like used in URLs, where address is suppounded with
[ … ].

unix – ADDRESS_PATTERN is shell-style wildcard.

packet – format looks like inet, only interface index
stays instead of port and link layer protocol id instead of address.

netlink – format looks like inet, only socket pid
stays instead of port and netlink channel instead of address.

PORT is syntactically ADDRESS_PATTERN with wildcard
address part. Certainly, it is undefined for UNIX sockets.

5.2 Environment variables

ss allows to change source of information using various
environment variables:

PROC_SLABINFO to override /proc/slabinfo

PROC_NET_TCP to override /proc/net/tcp

PROC_NET_UDP to override /proc/net/udp

etc.

Variable PROC_ROOT allows to change root of all the /proc/
hierarchy.

Variable TCPDIAG_FILE prescribes to open a file instead of
requesting kernel to dump information about TCP sockets.

This option is used mainly to investigate bug reports,
when dumps of files usually found in /proc/ are recevied
by e-mail.

5.3 Output format

Six columns. The first is Netid, it denotes socket type and
transport protocol, when it is ambiguous: tcp, udp, raw,
u_str is abbreviation for unix_stream, u_dgr for UNIX
datagram sockets, nl for netlink, p_raw and p_dgr for
raw and datagram packet sockets. This column is optional, it will
be hidden, if filter selects an unique netid.

The second column is State. Socket state is displayed here.
The names are standard TCP names, except for UNCONN, which
cannot happen for TCP, but normal for not connected sockets
of another types. Again, this column can be hidden.

Then two columns (Recv-Q and Send-Q) showing amount of data
queued for receive and transmit.

And the last two columns display local address and port of the socket
and its peer address, if the socket is connected.

If options -o, -e or -p were given, options are
displayed not in fixed positions but separated by spaces pairs:
option:value. If value is not a single number, it is presented
as list of values, enclosed to ( … ) and separated with
commas. F.e.



   timer:(keepalive,111min,0)

is typical format for TCP timer (option -o).



   users:((X,113,3))

is typical for list of users (option -p).

6. Some numbers

Well, let us use pidentd and a tool ibench to measure
its performance. It is 30 requests per second here. Nothing to test,
it is too slow. OK, let us patch pidentd with patch from directory
Patches. After this it handles about 4300 requests per second
and becomes handy tool to pollute socket tables with lots of timewait
buckets.

So, each test starts from pollution tables with 30000 sockets
and then doing full dump of the table piped to wc and measuring
timings with time:

Results:

netstat -at – 15.6 seconds

ss -atr, but without tcp_diag – 5.4 seconds

ss -atr with tcp_diag – 0.47 seconds

No comments. Though one comment is necessary, most of time
without tcp_diag is wasted inside kernel with completely
blocked networking. More than 10 seconds, yes. tcp_diag
does the same work for 100 milliseconds of system time.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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