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 val-
ues, instead of human-readable.
-r, --resolve
Try to resolve numeric address/ports.
-a, --all
Display both listening and non-listening (for TCP this means es-
tablished 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 retrans 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 occured
-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)
<ropt_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 received, 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-multi-
plexed into the socket
-p, --processes
Show process using socket.
-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 re-
ceived packets
fastopen
show string "fastopen" if the fastopen option is set
cong_alg
the congestion algorithm name, the default congestion al-
gorithm 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 millisec-
ond
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
millisecond
lastrcv:<lastrcv>
how long time since the last packet received, the unit is
millisecond
lastack:<lastack>
how long time since the last ack received, the unit is
millisecond
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 re-
ceive buffer
--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 priority set by SO_PRIORITY.
-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.
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 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.
--vsock
Display vsock sockets (alias for -f vsock).
--xdp Display XDP sockets (alias for -f xdp).
-f FAMILY, --family=FAMILY
Display sockets of type FAMILY. Currently the following fami-
lies are supported: unix, inet, inet6, link, netlink, vsock,
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, vsock_stream, vsock_dgram,
xdp Any item in the list may optionally be prefixed by an excla-
mation mark (!) to exclude that socket table 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 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
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)