SS(8) System Manager's Manual SS(8)
ss - another utility to investigate sockets
ss [options] [ FILTER ]
ss is used to dump socket statistics. It allows showing information
similar to netstat. It can display more TCP and state informations
than other tools.
When no option is used ss displays a list of open non-listening sockets
(e.g. TCP/UNIX/UDP) that have established connection.
Show summary of options.
Output version information.
Suppress header line.
Do not try to resolve service names.
Try to resolve numeric address/ports.
Display both listening and non-listening (for TCP this means
established connections) sockets.
Display only listening sockets (these are omitted by default).
Show timer information. For tcp protocol, the output format is:
the name of the timer, there are five kind of timer
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
how long time the timer will expire
how many times the retran occurs
Show detailed socket information. The output format is:
uid:<uid_number> ino:<inode_number> sk:<cookie>
the user id the socket belongs to
the socket's inode number in VFS
an uuid of the socket
Show socket memory usage. The output format is:
the memory allocated for receiving packet
the total memory can be allocated for receiving packet
the memory used for sending packet (which has been sent
to layer 3)
the total memory can be allocated for sending packet
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.
The memory allocated for sending packet (which has not
been sent to layer 3)
The memory used for storing socket option, e.g., the key
for TCP MD5 signature
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
Show process using socket.
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
show string "ecnseen" if the saw ecn flag is found in
show string "fastopen" if the fastopen option is set
the congestion algorithm name, the default congestion
algorithm is "cubic"
if window scale option is used, this field shows the send
scale factory and receive scale factory
tcp re-transmission timeout value, the unit is millisec-
used for exponential backoff re-transmission, the actual
re-transmission timeout value is icsk_rto << icsk_backoff
rtt is the average round trip time, rttvar is the mean
deviation of rtt, their units are millisecond
ack timeout, unit is millisecond, used for delay ack mode
max segment size
congestion window size
path MTU value
tcp congestion window slow start threshold
segments sent out
how long time since the last packet sent, the unit is
how long time since the last packet received, the unit is
how long time since the last ack received, the unit is
the pacing rate and max pacing rate
a helper variable for TCP internal auto tuning socket
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-
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
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-
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.
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.
Show socket BPF filters (only administrators are allowed to get
Display only IP version 4 sockets (alias for -f inet).
Display only IP version 6 sockets (alias for -f inet6).
Display PACKET sockets (alias for -f link).
Display TCP sockets.
Display UDP sockets.
Display DCCP sockets.
Display RAW sockets.
Display Unix domain sockets (alias for -f unix).
Display SCTP sockets.
Display vsock sockets (alias for -f vsock).
-f FAMILY, --family=FAMILY
Display sockets of type FAMILY. Currently the following fami-
lies are supported: unix, inet, inet6, link, netlink, vsock.
-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.
-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
-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
FILTER := [ state STATE-FILTER ] [ EXPRESSION ]
Please take a look at the official documentation for details
STATE-FILTER allows to construct arbitrary set of states to match. Its
syntax is sequence of keywords state and exclude followed by identifier
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 -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
List all the tcp sockets in state FIN-WAIT-1 for our apache to
network 193.233.7/24 and look at their timers.
RFC 793 - https://tools.ietf.org/rfc/rfc793.txt (TCP states)
ss was written by Alexey Kuznetsov, <email@example.com>.
This manual page was written by Michael Prokop <firstname.lastname@example.org> for the
Debian project (but may be used by others).
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