SS(8)
Investigate sockets. Static snapshot from Ubuntu 24.04.5 LTS.
SS(8) System Manager's Manual SS(8)
NAME
ss - another utility to investigate sockets
SYNOPSIS
ss [options] [ FILTER ]
DESCRIPTION
ss is used to dump socket statistics. It allows showing information similar to
netstat. It can display more TCP and state information than other tools.
OPTIONS
When no option is used ss displays a list of open non-listening sockets (e.g.
TCP/UNIX/UDP) that have established connection.
-h, --help
Show summary of options.
-V, --version
Output version information.
-H, --no-header
Suppress header line.
-O, --oneline
Print each socket's data on a single line.
-n, --numeric
Do not try to resolve service names. Show exact bandwidth values, in‐
stead of human-readable.
-r, --resolve
Try to resolve numeric address/ports.
-a, --all
Display both listening and non-listening (for TCP this means estab‐
lished connections) sockets.
-l, --listening
Display only listening sockets (these are omitted by default).
-o, --options
Show timer information. For TCP protocol, the output format is:
timer:(<timer_name>,<expire_time>,<retrans>)
<timer_name>
the name of the timer, there are five kind of timer names:
on : means one of these timers: TCP retrans timer, TCP early re‐
trans timer and tail loss probe timer
keepalive: tcp keep alive timer
timewait: timewait stage timer
persist: zero window probe timer
unknown: none of the above timers
<expire_time>
how long time the timer will expire
<retrans>
how many times the retransmission occurred
-e, --extended
Show detailed socket information. The output format is:
uid:<uid_number> ino:<inode_number> sk:<cookie>
<uid_number>
the user id the socket belongs to
<inode_number>
the socket's inode number in VFS
<cookie>
an uuid of the socket
-m, --memory
Show socket memory usage. The output format is:
skmem:(r<rmem_alloc>,rb<rcv_buf>,t<wmem_alloc>,tb<snd_buf>,
f<fwd_alloc>,w<wmem_queued>,o<opt_mem>,
bl<back_log>,d<sock_drop>)
<rmem_alloc>
the memory allocated for receiving packet
<rcv_buf>
the total memory can be allocated for receiving packet
<wmem_alloc>
the memory used for sending packet (which has been sent to layer
3)
<snd_buf>
the total memory can be allocated for sending packet
<fwd_alloc>
the memory allocated by the socket as cache, but not used for
receiving/sending packet yet. If need memory to send/receive
packet, the memory in this cache will be used before allocate
additional memory.
<wmem_queued>
The memory allocated for sending packet (which has not been sent
to layer 3)
<opt_mem>
The memory used for storing socket option, e.g., the key for TCP
MD5 signature
<back_log>
The memory used for the sk backlog queue. On a process context,
if the process is receiving packet, and a new packet is re‐
ceived, it will be put into the sk backlog queue, so it can be
received by the process immediately
<sock_drop>
the number of packets dropped before they are de-multiplexed
into the socket
-p, --processes
Show process using socket.
-T, --threads
Show thread using socket. Implies -p. -p.
-i, --info
Show internal TCP information. Below fields may appear:
ts show string "ts" if the timestamp option is set
sack show string "sack" if the sack option is set
ecn show string "ecn" if the explicit congestion notification option
is set
ecnseen
show string "ecnseen" if the saw ecn flag is found in received
packets
fastopen
show string "fastopen" if the fastopen option is set
cong_alg
the congestion algorithm name, the default congestion algorithm
is "cubic"
wscale:<snd_wscale>:<rcv_wscale>
if window scale option is used, this field shows the send scale
factor and receive scale factor
rto:<icsk_rto>
tcp re-transmission timeout value, the unit is millisecond
backoff:<icsk_backoff>
used for exponential backoff re-transmission, the actual re-
transmission timeout value is icsk_rto << icsk_backoff
rtt:<rtt>/<rttvar>
rtt is the average round trip time, rttvar is the mean deviation
of rtt, their units are millisecond
ato:<ato>
ack timeout, unit is millisecond, used for delay ack mode
mss:<mss>
max segment size
cwnd:<cwnd>
congestion window size
pmtu:<pmtu>
path MTU value
ssthresh:<ssthresh>
tcp congestion window slow start threshold
bytes_acked:<bytes_acked>
bytes acked
bytes_received:<bytes_received>
bytes received
segs_out:<segs_out>
segments sent out
segs_in:<segs_in>
segments received
send <send_bps>bps
egress bps
lastsnd:<lastsnd>
how long time since the last packet sent, the unit is millisec‐
ond
lastrcv:<lastrcv>
how long time since the last packet received, the unit is mil‐
lisecond
lastack:<lastack>
how long time since the last ack received, the unit is millisec‐
ond
pacing_rate <pacing_rate>bps/<max_pacing_rate>bps
the pacing rate and max pacing rate
rcv_space:<rcv_space>
a helper variable for TCP internal auto tuning socket receive
buffer
tcp-ulp-mptcp flags:[MmBbJjecv] token:<rem_token(rem_id)/loc_to‐
ken(loc_id)> seq:<sn> sfseq:<ssn> ssnoff:<off> maplen:<maplen>
MPTCP subflow information
--tos Show ToS and priority information. Below fields may appear:
tos IPv4 Type-of-Service byte
tclass IPv6 Traffic Class byte
class_id
Class id set by net_cls cgroup. If class is zero this shows pri‐
ority set by SO_PRIORITY.
--cgroup
Show cgroup information. Below fields may appear:
cgroup Cgroup v2 pathname. This pathname is relative to the mount point
of the hierarchy.
--tipcinfo
Show internal tipc socket information.
-K, --kill
Attempts to forcibly close sockets. This option displays sockets
that are successfully closed and silently skips sockets that the
kernel does not support closing. It supports IPv4 and IPv6 sock‐
ets only.
-s, --summary
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.
-E, --events
Continually display sockets as they are destroyed
-Z, --context
As the -p option but also shows process security context. If the
-T option is used, also shows thread security context.
For netlink(7) sockets the initiating process context is dis‐
played as follows:
1. If valid pid show the process context.
2. If destination is kernel (pid = 0) show kernel ini‐
tial context.
3. If a unique identifier has been allocated by the ker‐
nel or netlink user, show context as "unavailable".
This will generally indicate that a process has more
than one netlink socket active.
-z, --contexts
As the -Z option but also shows the socket context. The socket
context is taken from the associated inode and is not the actual
socket context held by the kernel. Sockets are typically labeled
with the context of the creating process, however the context
shown will reflect any policy role, type and/or range transition
rules applied, and is therefore a useful reference.
-N NSNAME, --net=NSNAME
Switch to the specified network namespace name.
-b, --bpf
Show socket classic BPF filters (only administrators are allowed
to get these information).
-4, --ipv4
Display only IP version 4 sockets (alias for -f inet).
-6, --ipv6
Display only IP version 6 sockets (alias for -f inet6).
-0, --packet
Display PACKET sockets (alias for -f link).
-t, --tcp
Display TCP sockets.
-u, --udp
Display UDP sockets.
-d, --dccp
Display DCCP sockets.
-w, --raw
Display RAW sockets.
-x, --unix
Display Unix domain sockets (alias for -f unix).
-S, --sctp
Display SCTP sockets.
--tipc Display tipc sockets (alias for -f tipc).
--vsock
Display vsock sockets (alias for -f vsock).
--xdp Display XDP sockets (alias for -f xdp).
-M, --mptcp
Display MPTCP sockets.
--inet-sockopt
Display inet socket options.
-f FAMILY, --family=FAMILY
Display sockets of type FAMILY. Currently the following fami‐
lies are supported: unix, inet, inet6, link, netlink, vsock,
tipc, xdp.
-A QUERY, --query=QUERY, --socket=QUERY
List of socket tables to dump, separated by commas. The follow‐
ing identifiers are understood: all, inet, tcp, udp, raw, unix,
packet, netlink, unix_dgram, unix_stream, unix_seqpacket,
packet_raw, packet_dgram, dccp, sctp, tipc, vsock_stream,
vsock_dgram, xdp, mptcp. Any item in the list may optionally be
prefixed by an exclamation mark (!) to exclude that socket ta‐
ble from being dumped.
-D FILE, --diag=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, --filter=FILE
Read filter information from FILE. Each line of FILE is inter‐
preted like single command line option. If FILE is - stdin is
used.
FILTER := [ state STATE-FILTER ] [ EXPRESSION ]
Please take a look at the official documentation for details re‐
garding filters.
STATE-FILTER
STATE-FILTER allows one 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, 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
EXPRESSION
EXPRESSION allows filtering based on specific criteria. EXPRESSION consists
of a series of predicates combined by boolean operators. The possible opera‐
tors in increasing order of precedence are or (or | or ||), and (or & or &&),
and not (or !). If no operator is between consecutive predicates, an implicit
and operator is assumed. Subexpressions can be grouped with "(" and ")".
The following predicates are supported:
{dst|src} [=] HOST
Test if the destination or source matches HOST. See HOST SYNTAX for de‐
tails.
{dport|sport} [OP] [FAMILY:]:PORT
Compare the destination or source port to PORT. OP can be any of "<",
"<=", "=", "!=", ">=" and ">". Following normal arithmetic rules. FAM‐
ILY and PORT are as described in HOST SYNTAX below.
dev [=|!=] DEVICE
Match based on the device the connection uses. DEVICE can either be a
device name or the index of the interface.
fwmark [=|!=] MASK
Matches based on the fwmark value for the connection. This can either
be a specific mark value or a mark value followed by a "/" and a bit‐
mask of which bits to use in the comparison. For example "fwmark =
0x01/0x03" would match if the two least significant bits of the fwmark
were 0x01.
cgroup [=|!=] PATH
Match if the connection is part of a cgroup at the given path.
autobound
Match if the port or path of the source address was automatically allo‐
cated (rather than explicitly specified).
Most operators have aliases. If no operator is supplied "=" is assumed. Each
of the following groups of operators are all equivalent:
• = == eq
• != ne neq
• > gt
• < lt
• >= ge geq
• <= le leq
• ! not
• | || or
• & && and
HOST SYNTAX
The general host syntax is [FAMILY:]ADDRESS[:PORT].
FAMILY must be one of the families supported by the -f option. If not given it
defaults to the family given with the -f option, and if that is also missing,
will assume either inet or inet6. Note that all host conditions in the expres‐
sion should either all be the same family or be only inet and inet6. If there
is some other mixture of families, the results will probably be unexpected.
The form of ADDRESS and PORT depends on the family used. "*" can be used as a
wildcard for either the address or port. The details for each family are as
follows:
unix ADDRESS is a glob pattern (see fnmatch(3)) that will be matched case-
insensitively against the unix socket's address. Both path and abstract
names are supported. Unix addresses do not support a port, and "*" can‐
not be used as a wildcard.
link ADDRESS is the case-insensitive name of an Ethernet protocol to match.
PORT is either a device name or a device index for the desired link de‐
vice, as seen in the output of ip link.
netlink
ADDRESS is a descriptor of the netlink family. Possible values come
from /etc/iproute2/nl_protos. PORT is the port id of the socket, which
is usually the same as the owning process id. The value "kernel" can be
used to represent the kernel (port id of 0).
vsock ADDRESS is an integer representing the CID address, and PORT is the
port.
inet and inet6
ADDRESS is an ip address (either v4 or v6 depending on the family) or a
DNS hostname that resolves to an ip address of the required version. An
ipv6 address must be enclosed in "[" and "]" to disambiguate the port
separator. The address may additionally have a prefix length given in
CIDR notation (a slash followed by the prefix length in bits). PORT is
either the numerical socket port, or the service name for the port to
match.
USAGE EXAMPLES
ss -t -a
Display all TCP sockets.
ss -t -a -Z
Display all TCP sockets with process SELinux security contexts.
ss -u -a
Display all UDP sockets.
ss -o state established '( dport = :ssh or sport = :ssh )'
Display all established ssh connections.
ss -x src /tmp/.X11-unix/*
Find all local processes connected to X server.
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 -a -A 'all,!tcp'
List sockets in all states from all socket tables but TCP.
SEE ALSO
ip(8),
RFC 793 - https://tools.ietf.org/rfc/rfc793.txt (TCP states)
AUTHOR
ss was written by Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>.
This manual page was written by Michael Prokop <mika@grml.org> for the Debian
project (but may be used by others).
SS(8)
Generated 2026-11-02 from the manual installed on node.spa-dev-dh.xyz. Original copyright and license terms apply.