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 information 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.

-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, instead of human-readable.
-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 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-multiplexed 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 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 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
--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 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.
-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 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.
--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 families 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 following 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 exclamation 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 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 for details regarding filters.

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

ip(8),
RFC 793 - https://tools.ietf.org/rfc/rfc793.txt (TCP states)

ss was written by Alexey Kuznetsov, <kuznet>.