A UNIX Command
$skill
Usage:   skill [signal to send] [options] process selection criteria
Example: skill -KILL -v pts/*

The default signal is TERM. Use -l or -L to list available signals.
Particularly useful signals include HUP, INT, KILL, STOP, CONT, and 0.
Alternate signals may be specified in three ways: -SIGKILL -KILL -9

General options:
-f  fast mode            This is not currently useful.
-i  interactive use      You will be asked to approve each action.
-v  verbose output       Display information about selected processes.
-w  warnings enabled     This is not currently useful.
-n  no action            This only displays the process ID.

Selection criteria can be: terminal, user, pid, command.
The options below may be used to ensure correct interpretation.
-t  The next argument is a terminal (tty or pty).
-u  The next argument is a username.
-p  The next argument is a process ID number.
-c  The next argument is a command name.
$skill -l
HUP INT QUIT ILL TRAP ABRT BUS FPE KILL USR1 SEGV USR2 PIPE ALRM TERM STKFLT
CHLD CONT STOP TSTP TTIN TTOU URG XCPU XFSZ VTALRM PROF WINCH POLL PWR SYS
$ps aux | grep xine
jeffrin   2844  2.9  1.4 661236 29460 pts/3    Sl   20:44   0:00 xine
jeffrin   2866  0.0  0.0 112944   816 pts/1    S+   20:44   0:00 grep xine
$skill 2844
$ps aux | grep xine
jeffrin   2869  0.0  0.0 112944   820 pts/1    S+   20:44   0:00 grep xine
$

UNIX Explanation
The default  signal for  skill is TERM.  Use -l or  -L to
list  available  signals.   Particularly  useful  signals
include  HUP, INT,  KILL, STOP,  CONT, and  0.  Alternate
signals  may  be specified  in  three  ways: -9  -SIGKILL
-KILL.

A UNIX Parameter
$cat /proc/sys/net/ipv4/tcp_retries1
3
$echo 4 > /proc/sys/net/ipv4/tcp_r

Parameter Definition
This value influences the  time, after which TCP decides,
that  something  is   wrong  due  to  unacknowledged  RTO
retransmissions,  and  reports   this  suspicion  to  the
network   layer.   RFC   1122  recommends   at   least  3
retransmissions, which is the default.

Parameter Code Internals


snippet 1
{
.procname = "tcp_retries1",
.data = &sysctl_tcp_retries1,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_minmax,
.extra2 = &tcp_retr1_max
},

snippet 2
if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
/* Black hole detection */
tcp_mtu_probing(icsk, sk);

dst_negative_advice(sk);
}


Related From Research Paper
In this paper we have investigated TCP behavior in a 802.11b wireless Infrastructure network by means of experiments in a wireless network testbed. We have compared results obtained with similar experiments done in NS2 simulator. We conclude that TCP ACK skipping indeed improves TCP performance in real-life wireless LANs. Although the original goal was to explore the simultaneous-send problem reported in [1], several other insights were also obtained. The NS2 simulations showed the simultaneous-send problem manifest when MAC retries were disabled. However we were unable to reproduce the NO MAC retries case. Unlike in the NS2 simulator, various status indicators cannot be tracked in real experimentation. Instead the simultaneous-send phenomenon was observed using standalone network sniffers.
source: Experimental Evaluation of the TCP Simultaneous-Send Problem in 802.11 Wireless Local Area Networks Sumathi Gopal WINLAB, Rutgers University 73, Brett Road Piscataway, NJ 08854-8048 001 609 720 1202 sumathi@winlab.rutgers.edu Dipankar Raychaudhuri WINLAB, Rutgers University 73, Brett Road Piscataway, NJ 08854-8048 001 732 445 0877 ray@winlab.rutgers.edu
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