我如何使用bash指定进程的顶级父PID？ [英] How do I find the top-level parent PID of a given process using bash?

问题描述

比方说，我跑 PS AXF ，我可以看到我的命令的进程树看起来是这样的：

Let's say I run ps axf and I can see that my command's process tree looks like this:

  800 ?        Ss     0:00 /usr/sbin/sshd
10186 ?        Ss     0:00  \_ sshd: yukondude [priv]
10251 ?        S      0:00      \_ sshd: yukondude@pts/0
10252 pts/0    Ss     0:00          \_ -bash
10778 pts/0    S      0:00              \_ su -
10785 pts/0    S      0:00                  \_ -su
11945 pts/0    R+     0:00                      \_ ps axf

我知道我可以检查 $ 当前shell的PID（10785）或 $ PPID 父PID（10778）。

I know I can check $$ for the current shell's PID (10785) or $PPID for the parent PID (10778).

但我只想顶级父PID，这将是在这个例子中800（SSH守护进程）。有没有办法做到这一点容易吗？

But I just want the top-level parent PID, which would be 800 (SSH daemon) in this example. Is there any way to do that easily?

我从<有学问href=\"http://stackoverflow.com/questions/1525605/linux-programmatically-get-parent-pid-of-another-process/1525673#1525673\">this SO回答，我可以递归查询在第4项的/ proc / PID / STAT 文件中查找每个进程的父PID：

I learned from this SO answer that I can recursively check the 4th entry in the /proc/PID/stat file to find each process's parent PID:

# cut -f4 -d' ' /proc/10785/stat
10778
# cut -f4 -d' ' /proc/10778/stat
10252
# cut -f4 -d' ' /proc/10252/stat
10251
# cut -f4 -d' ' /proc/10251/stat
10186
# cut -f4 -d' ' /proc/10186/stat
800
# cut -f4 -d' ' /proc/800/stat
1

（顶层父PID将是我到达之前一的init 的PID，即，1）

在我写一个小环（我甚至不知道是否可以使用在bash递归），要做到这一点，有没有我缺少一个更简单的方法是什么？也许只是一个在的/ proc 文件的参数？ A 的grep 通过这些文件并没有透露任何明显。

Before I write a little loop (I'm not even sure if you can use recursion in bash) to do this, is there a much more straightforward method that I'm missing? Maybe just another parameter of a file under /proc? A grep through those files didn't reveal anything obvious.

修改：当然，对于所有Linux进程顶级工艺/ sbin目录/初始化为1。PID我要的是家长之前只是的PID：倒数第二家长。

Edit: Of course, the top-level process for all Linux processes is /sbin/init with a PID of 1. What I want is the PID of the parent just before that: the penultimate parent.

推荐答案

失败一个更好的解决方案，这里有一个简单的（递归）脚本，让你给它的进程号的顶级父PID（或当前shell，如果你离开了PID参数）：

Failing a better solution, here's a simple (recursive) script to get the top-level parent PID of any process number you give it (or the current shell if you leave out the PID argument):

#!/bin/bash
# Look up the top-level parent Process ID (PID) of the given PID, or the current
# process if unspecified.

function top_level_parent_pid {
    # Look up the parent of the given PID.
    pid=${1:-$$}
    stat=($(</proc/${pid}/stat))
    ppid=${stat[3]}

    # /sbin/init always has a PID of 1, so if you reach that, the current PID is
    # the top-level parent. Otherwise, keep looking.
    if [[ ${ppid} -eq 1 ]] ; then
        echo ${pid}
    else
        top_level_parent_pid ${ppid}
    fi
}

只是源这个脚本，并调用 top_level_parent_pid 带或不带PID参数，如合适的。

Just source this script and call top_level_parent_pid with or without a PID argument, as appropriate.

感谢@Dennis威廉姆森为他如何紧凑，有效地写这个剧本的许多建议。

Thanks to @Dennis Williamson for his many suggestions on how to write this script compactly and efficiently.

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