Question

我在bash（RHEL 5.3版本3.2.25）上看到一个非常非常奇怪的行为。

我有一个'Launcher'脚本执行以下操作（作为前台进程，在一个始终保持打开的终端中运行）：

它在后台启动程序A，然后退出。
A，然后在后台启动程序B的两个（进程）实例（例如：B1，B2）;
A，还在后台启动一个程序C实例。

上面的想法主要是让A，C和两个B相互通信，直到它们被用户杀死。（他们继续使用while sleep DURATION; do ... ; done循环运行。）

问题：

完成上述3个步骤后，当我从另一个终端窗口重复发出ps -ef时，我有时会看到一些额外的虚假B实例（比如说B3，B4 .. 。）和/或有时会列出一个额外的，虚假的A实例！

这些额外的实例是短暂的 - 它们来自ps -ef列表。

此外，这些虚假实例恰好是有效（或期望）过程的子项 - 而不是兄弟姐妹。例如，B3和B4将分别列出B1和B2作为其父级;同样，假的A2会将A列为其父级！

现在，我 PRETTY DARNED DARNED SURE 我 NO WAY 从B中创建任何其他B实例，也不从A内部创建任何A实例。

那么，这里发生了什么？

非常感谢，提前。

PS：我已经看到了类似的问题（多个虚假实例），一段时间回到cron作业的上下文中，这些作业被设计为在首次启动时无限期地挂起。在这里，我会看到我的cron作业的多个实例，即使我有明确的逻辑来阻止crond启动任何其他实例（通过检查磁盘上是否存在锁定文件）。而且，即使在这里，我也无法弄清楚问题。

$ ps -ejfH 
UID        PID  PPID  PGID   SID  C STIME TTY          TIME CMD
root     28503     1 28474 11126  0 22:14 pts/1    00:00:31   /bin/bash A
root     28525 28503 28474 11126  0 22:14 pts/1    00:00:26     /bin/bash B 
root     16143 28525 28474 11126  0 23:14 pts/1    00:00:00       [B] <defunct>
root     16144 28525 28474 11126  0 23:14 pts/1    00:00:00       /bin/bash B 
root     28531 28503 28474 11126  0 22:14 pts/1    00:00:23     /bin/bash B 
root     28566 28503 28474 11126  0 22:14 pts/1    00:00:01     /bin/bash C

$ ps -ejfH 
UID        PID  PPID  PGID   SID  C STIME TTY          TIME CMD
root     28503     1 28474 11126  0 22:14 pts/1    00:00:31   /bin/bash A
root     28525 28503 28474 11126  0 22:14 pts/1    00:00:26     /bin/bash B 
root     28531 28503 28474 11126  0 22:14 pts/1    00:00:23     /bin/bash B 
root     28566 28503 28474 11126  0 22:14 pts/1    00:00:01     /bin/bash C
root     18579 28503 28474 11126  0 23:14 pts/1    00:00:00     /bin/bash A

$ ps -ejfH
UID        PID  PPID  PGID   SID  C STIME TTY          TIME CMD
root     28503     1 28474 11126  0 22:14 pts/1    00:00:31   /bin/bash A
root     28525 28503 28474 11126  0 22:14 pts/1    00:00:26     /bin/bash B 
root     22717 28525 28474 11126  0 23:14 pts/1    00:00:00       /bin/bash B 
root     22718 22717 28474 11126  0 23:14 pts/1    00:00:00         /bin/bash B 
root     28531 28503 28474 11126  0 22:14 pts/1    00:00:23     /bin/bash B 
root     28566 28503 28474 11126  0 22:14 pts/1    00:00:01     /bin/bash C

$ ps -ejfH
UID        PID  PPID  PGID   SID  C STIME TTY          TIME CMD
root     28503     1 28474 11126  0 22:14 pts/1    00:00:31   /bin/bash A
root     28525 28503 28474 11126  0 22:14 pts/1    00:00:26     /bin/bash B 
root     28531 28503 28474 11126  0 22:14 pts/1    00:00:23     /bin/bash B 
root     28566 28503 28474 11126  0 22:14 pts/1    00:00:01     /bin/bash C

$ ps -ejfH
UID        PID  PPID  PGID   SID  C STIME TTY          TIME CMD
root     28503     1 28474 11126  0 22:14 pts/1    00:00:32   /bin/bash A
root     28525 28503 28474 11126  0 22:14 pts/1    00:00:27     /bin/bash B 
root     28531 28503 28474 11126  0 22:14 pts/1    00:00:24     /bin/bash B 
root     32021 28531 28474 11126  0 23:15 pts/1    00:00:00       /bin/bash B 
root     32023 32021 28474 11126  0 23:15 pts/1    00:00:00         [B] <defunct>
root     28566 28503 28474 11126  0 22:14 pts/1    00:00:01     /bin/bash C
root     32013 28503 28474 11126  0 23:15 pts/1    00:00:00     /bin/bash A

$ ps -ejfH
UID        PID  PPID  PGID   SID  C STIME TTY          TIME CMD
root     28503     1 28474 11126  0 22:14 pts/1    00:00:32   /bin/bash A
root     28525 28503 28474 11126  0 22:14 pts/1    00:00:27     /bin/bash B 
root     28531 28503 28474 11126  0 22:14 pts/1    00:00:24     /bin/bash B 
root     28566 28503 28474 11126  0 22:14 pts/1    00:00:01     /bin/bash C
root      2310 28503 28474 11126  0 23:15 pts/1    00:00:00     /bin/bash A
root      2324  2310 28474 11126  0 23:15 pts/1    00:00:00       /bin/bash A

$ ps -ejfH
UID        PID  PPID  PGID   SID  C STIME TTY          TIME CMD
root     28503     1 28474 11126  0 22:14 pts/1    00:00:32   /bin/bash A
root     28525 28503 28474 11126  0 22:14 pts/1    00:00:27     /bin/bash B 
root     28531 28503 28474 11126  0 22:14 pts/1    00:00:24     /bin/bash B 
root      9219 28531 28474 11126  0 23:16 pts/1    00:00:00       [B] <defunct>
root     28566 28503 28474 11126  0 22:14 pts/1    00:00:02     /bin/bash C

$ ps -ejfH
UID        PID  PPID  PGID   SID  C STIME TTY          TIME CMD
root     28503     1 28474 11126  0 22:14 pts/1    00:00:32   /bin/bash A
root     28525 28503 28474 11126  0 22:14 pts/1    00:00:27     /bin/bash B 
root     28531 28503 28474 11126  0 22:14 pts/1    00:00:24     /bin/bash B 
root     28566 28503 28474 11126  0 22:14 pts/1    00:00:02     /bin/bash C
root      9692 28503 28474 11126  0 23:16 pts/1    00:00:00     /bin/bash A

$ ps -ejfH
UID        PID  PPID  PGID   SID  C STIME TTY          TIME CMD
root     28503     1 28474 11126  0 22:14 pts/1    00:00:33   /bin/bash A
root     28525 28503 28474 11126  0 22:14 pts/1    00:00:27     /bin/bash B 
root     28531 28503 28474 11126  0 22:14 pts/1    00:00:24     /bin/bash B 
root     28566 28503 28474 11126  0 22:14 pts/1    00:00:02     /bin/bash C
root     15686 28503 28474 11126  0 23:16 pts/1    00:00:00     /bin/bash A

Answer 1

有许多bash功能可以生成子shell来执行脚本的一部分。我的猜测是你的A和B脚本正在使用其中的一些功能。除了通过在( ... )中包含命令显式创建子shell之外，还将为在管道中运行的任何bash命令，命令替换（$( ... )或反引号）创建子shell，或者使用{{ 1}}。这是一个说明这些内容的脚本：

（注意：在$ cat a #!/bin/bash echo "Initial subshell count: $BASH_SUBSHELL" ps -opid,ppid,command | egrep "PID|bash ./a" echo "input" | while read line; do echo "Subshell count in pipeline: $BASH_SUBSHELL" ps -opid,ppid,command | egrep "PID|bash ./a" done output=$(echo "Subshell count in \$(): $BASH_SUBSHELL" ps -opid,ppid,command | egrep "PID|bash ./a" ) echo "$output" ( echo "Subshell count in (): $BASH_SUBSHELL" ps -opid,ppid,command | egrep "PID|bash ./a" ) { echo "Subshell count in backgrounded command: $BASH_SUBSHELL" ps -opid,ppid,command | egrep "PID|bash ./a" } & sleep 1 $ ./a Initial subshell count: 0 PID PPID COMMAND 1410 158 /bin/bash ./a 1412 1410 egrep PID|bash ./a Subshell count in pipeline: 1 PID PPID COMMAND 1410 158 /bin/bash ./a 1414 1410 /bin/bash ./a 1416 1414 egrep PID|bash ./a Subshell count in $(): 1 PID PPID COMMAND 1410 158 /bin/bash ./a 1417 1410 /bin/bash ./a 1419 1417 egrep PID|bash ./a Subshell count in (): 1 PID PPID COMMAND 1410 158 /bin/bash ./a 1420 1410 /bin/bash ./a 1422 1420 egrep PID|bash ./a Subshell count in backgrounded command: 1 PID PPID COMMAND 1410 158 /bin/bash ./a 1423 1410 /bin/bash ./a 1426 1423 egrep PID|bash ./a示例中，echo ... | while ...和while循环都在子shell中执行;但echo命令退出的速度太快，echo无法显示它。）

bash发布了额外的虚假后台进程

1 个答案: