How to determine the socket connection up time on Linux

You can try the following:

1. get the PID (say $pid) of the program by adding the -p option to netstat.

2. identify the proper line in the /proc/net/tcp file by looking at the local_address and/or rem_address fields (note that they are in hex format, specifically the IP address is expressed in little-endian byte order), also make sure that the st is 01 (for ESTABLISHED);

3. note the associated inode field (say $inode);

4. search for that inode among the file descriptors in /proc/$pid/fd and finally query the file access time of the symbolic link:

   find /proc/$pid/fd -lname "socket:\[$inode\]" -printf %t
   

---

That is a grunt work... here's a script (stub) to automatize the above points, it requires the remote address and it prints the socket uptime in seconds:

function suptime() {
    local addr=${1:?Specify the remote IPv4 address}
    local port=${2:?Specify the remote port number}
    # convert the provided address to hex format
    local hex_addr=$(python -c "import socket, struct; print(hex(struct.unpack('<L', socket.inet_aton('$addr'))[0])[2:10].upper().zfill(8))")
    local hex_port=$(python -c "print(hex($port)[2:].upper().zfill(4))")
    # get the PID of the owner process
    local pid=$(netstat -ntp 2>/dev/null | awk '$6 == "ESTABLISHED" && $5 == "'$addr:$port'"{sub("/.*", "", $7); print $7}')
    [ -z "$pid" ] && { echo 'Address does not match' 2>&1; return 1; }
    # get the inode of the socket
    local inode=$(awk '$4 == "01" && $3 == "'$hex_addr:$hex_port'" {print $10}' /proc/net/tcp)
    [ -z "$inode" ] && { echo 'Cannot lookup the socket' 2>&1; return 1; }
    # query the inode status change time
    local timestamp=$(find /proc/$pid/fd -lname "socket:\[$inode\]" -printf %T@)
    [ -z "$timestamp" ] && { echo 'Cannot fetch the timestamp' 2>&1; return 1; }
    # compute the time difference
    LANG=C printf '%s (%.2fs ago)\n' "$(date -d @$timestamp)" $(bc <<<"$(date +%s.%N) - $timestamp")
}

(Edit thanks to Alex for the fixes)

Example:

$ suptime 93.184.216.34 80
Thu Dec 24 16:22:58 CET 2015 (46.12s ago)

This questions was helpful to me, but I found using lsof instead of netstat let me avoid all the HEX stuff:

For a process ${APP} run by user ${USER}, the following returns all the open sockets to the IP address ${IP}:

PEEID=$(sudo pgrep -u ${USER} ${APP}) && for i in `sudo lsof -anP -i -u logstash | grep ${IP} | awk '{print $6}'` ; do echo "${device} time" ; sudo find /proc/${PEEID}/fd -lname "socket:\[${device}\]" -printf %t 2> /dev/null  ; echo  ;  done

The lsof contains the PID too, but I am not sure how to get it and the device number.

This was tested on Amazon Linux.

The script by cYrus worked for me but i had to fix it a bit (to get rid of a "L" in the hex address and to make port a 4 digit hex):

--- suptime.orig    2015-08-20 15:46:12.896652464 +0200
+++ suptime 2015-08-20 15:47:48.560074728 +0200
@@ -7,8 +7,8 @@
     hex_addr=$(python -c "
 import socket, struct;
 print hex(struct.unpack('<L',
-socket.inet_aton('$addr'))[0])[2:].upper().zfill(8)")
-    hex_port=$(python -c "print hex($port)[2:].upper()")
+socket.inet_aton('$addr'))[0])[2:10].upper().zfill(8)")
+    hex_port=$(python -c "print hex($port)[2:].upper().zfill(4)")
     inode=$(awk '$3 == "'$hex_addr:$hex_port'" {print $10}' /proc/net/tcp)
     time=$(find /proc/$pid/fd -lname "socket:\[$inode\]" -printf %A@)
     LANG=C printf '%.2fs' $(bc <<<"$(date +%s.%N) - $time")