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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 informations 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.
-n, --numeric
Do not try to resolve service names.
-r, --resolve
Try to resolve numeric address/ports.
-a, --all
Display both listening and non-listening (for TCP this means established 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 retran occurs
-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>)
<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 received, it will be put into the sk backlog queue, so it can be received by the process immediately
-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 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 factory and receive scale factory
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
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 receive buffer
-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 sockets 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.
-Z, --context
As the -p option but also shows process security context.
 
For netlink(7) sockets the initiating process context is displayed as follows:
1.
If valid pid show the process context.
2.
If destination is kernel (pid = 0) show kernel initial context.
3.
If a unique identifier has been allocated by the kernel 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.
-f FAMILY, --family=FAMILY
Display sockets of type FAMILY. Currently the following families are supported: unix, inet, inet6, link, netlink.
-A QUERY, --query=QUERY, --socket=QUERY
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, unix_seqpacket, packet_raw, packet_dgram, dccp, sctp.
-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 interpreted like single command line option. If FILE is - stdin is used.
FILTER := [ state STATE-FILTER ] [ EXPRESSION ]
Please take a look at the official documentation (Debian package iproute-doc) 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 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.

SEE ALSO

ip(8), /usr/share/doc/iproute-doc/ss.html (package iproute­doc),
 
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).