#!/usr/bin/perl -wuse strict;#white listmy @ALLOW_USERS = qw{  test  root  lulu1};#the maximum number of ssh loginmy $LOGIN_TIMES = 1;sub main{  my @lines = `ps -eo user,pid,etime,cmd | grep sshd`;  my $users;  for my $line (@lines) {    if(my ($user, $pid, $etime, $cmd) = $line =~ /^([^/s]+)/s+(/d+)/s+([^/s]+)/s+(sshd:.+)$/) {      next if grep {$user eq $_} @ALLOW_USERS;      my $proc = {'pid', $pid, 'etime', $etime, 'cmd', $cmd};      push @{$users->{$user}}, $proc;    }  }  for my $key(keys(%$users)) {     my @sshs = sort {      my ($lb, $la) = (length($b->{'etime'}), length($a->{'etime'}));      if($lb == $la) {        $b->{'etime'} cmp $a->{'etime'};      } else {        $lb <=> $la;      }    } @{$users->{$key}};    $LOGIN_TIMES = 1 if $LOGIN_TIMES < 1;    for (1 .. $LOGIN_TIMES) { pop @sshs; };    for my $ssh (@sshs) {      kill 9, $ssh->{'pid'};    }  }}while(1) {  main;  sleep 3;}

echo "/root/limit.pl &" >> /etc/rc.d/rc.local （加入開機啟動）/root/limit.pl & （運行腳本）