linux + ssh 限制 + ssh 同时从多台机器到一台机器

Question

下面的脚本“testssh.ksh”证明当我们尝试同时从多台机器执行ssh时ssh有一些问题

实际上这个脚本的目标是验证Solaris服务器(10.10.18.6)中/var/tmp下的文件test_file，正如大家看到的一些ssh步骤我们无法验证test_file 的存在，因为 ssh 卡住或未从 expect 激活

背景 - 此脚本同时对 IP - 10.10.18.6 的 Solaris 服务器执行 15 次 ssh，以验证服务器中/var/tmp 下的 file_test

我的问题-如何改进ssh进程以避免以下问题

备注 - 在这种情况下 sleep 可以帮助我们 - 但我不想在 ssh 进程之前添加 sleep

  [root@linux /var/tmp]# more  testssh.ksh
  #!/bin/ksh



  expect=`cat << EOF
  set timeout -1
  spawn  ssh  10.10.18.6 
       expect {
                 ")?"   { send "yes\r"  ; exp_continue  }

                 word:  {send pass123\r}
              }
  expect >  {send "ls  /var/tmp/test_file\r"}
  expect >    {send exit\r}
  expect eof
  EOF`


  for i in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
  do
     ( expect -c  "$expect"  | grep "test_file"  | grep -v ls ) &
  done

示例 - 当我们运行脚本 testssh.ksh 时

     [root@linux /var/tmp]# /var/tmp/testssh.ksh
     /var/tmp/test_file
     /var/tmp/test_file
     /var/tmp/test_file
     /var/tmp/test_file
     /var/tmp/test_file
     expect: spawn id exp6 not open
     while executing
     "expect >  {send "ls  /var/tmp/test_file\r"}"
     expect: spawn id exp6 not open
     while executing
     "expect >  {send "ls  /var/tmp/test_file\r"}"
     expect: spawn id exp6 not open
     while executing
     "expect >  {send "ls  /var/tmp/test_file\r"}"
     expect: spawn id exp6 not open
     while executing
     "expect >  {send "ls  /var/tmp/test_file\r"}"
     /var/tmp/test_file
     /var/tmp/test_file
     /var/tmp/test_file
     /var/tmp/test_file
     /var/tmp/test_file
     /var/tmp/test_file

Answer 1

您是否在 sshd.conf(或等效文件)中设置了 MaxSession 和 MaxStartups？我相信 40 个并发 SSH 连接对于您的服务器来说应该不会太多。

来自 man sshd_config 页面:

 MaxSessions
         Specifies the maximum number of open sessions permitted per net‐
         work connection.  The default is 10.

 MaxStartups
         Specifies the maximum number of concurrent unauthenticated con‐
         nections to the SSH daemon.  Additional connections will be
         dropped until authentication succeeds or the LoginGraceTime
         expires for a connection.  The default is 10.

         Alternatively, random early drop can be enabled by specifying the
         three colon separated values “start:rate:full” (e.g. "10:30:60").
         sshd(8) will refuse connection attempts with a probability of
         “rate/100” (30%) if there are currently “start” (10) unauthenti‐
         cated connections.  The probability increases linearly and all
         connection attempts are refused if the number of unauthenticated
         connections reaches “full” (60).

如果您没有更改这些，您的服务器将不会同时处理超过 10 个连接。

Similar question (serverfault.com)。