Linux 上一个进程如何拦截另一个进程的 stdout 和 stderr？

发布于 2024-07-08 07:22:31 字数 370 浏览 20 评论 0原文

我有一些应该停止运行的脚本，但它们却永远存在。有什么方法可以让我以可读的方式弄清楚他们正在向 STDOUT 和 STDERR 写入什么内容？

例如，我尝试这样做：

$ tail -f /proc/(pid)/fd/1

但这并没有真正起作用。无论如何，这是一个远景。

还有其他想法吗？

strace 本身就非常冗长且不可读。

注意：我只对他们的输出感兴趣，对其他任何东西都不感兴趣。其他的事情我有能力自己解决；这个问题仅关注于启动正在运行的进程后获取其stdout 和stderr 的访问权限。

原文

I have some scripts that ought to have stopped running but hang around forever. Is there some way I can figure out what they're writing to STDOUT and STDERR in a readable way?

I tried, for example, to do:

$ tail -f /proc/(pid)/fd/1

but that doesn't really work. It was a long shot anyway.

Any other ideas?

strace on its own is quite verbose and unreadable for seeing this.

Note: I am only interested in their output, not in anything else. I'm capable of figuring out the other things on my own; this question is only focused on getting access to stdout and stderr of the running process after starting it.

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安静被遗忘 2024-07-15 07:22:31

由于我不允许编辑 Jauco 的答案，因此我将给出对我有用的完整答案（Russell 的页面依赖于无保证的行为，如果您关闭 STDOUT 的文件描述符 1，则下一个 creat 调用将打开 FD 1。

因此，运行一个简单的无尽脚本，如下所示：

import time

while True:
    print 'test'
    time.sleep(1)

将其保存到 test.py，运行

$ python test.py

Get the PID:

$ ps auxw | grep test.py

Now, Attach gdb:

$ gdb -p (pid)

并执行 fd 魔法：

(gdb) call creat("/tmp/stdout", 0600)
$1 = 3
(gdb) call dup2(3, 1)
$2 = 1

现在您可以 tail /tmp/stdout 并查看过去用于 STDOUT 的输出。

Since I'm not allowed to edit Jauco's answer, I'll give the full answer that worked for me (Russell's page relies on un-guaranteed behaviour that, if you close file descriptor 1 for STDOUT, the next creat call will open FD 1.

So, run a simple endless script like this:

import time

while True:
    print 'test'
    time.sleep(1)

Save it to test.py, run with

$ python test.py

Get the PID:

$ ps auxw | grep test.py

Now, attach gdb:

$ gdb -p (pid)

and do the fd magic:

(gdb) call creat("/tmp/stdout", 0600)
$1 = 3
(gdb) call dup2(3, 1)
$2 = 1

Now you can tail /tmp/stdout and see the output that used to go to STDOUT.

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硬不硬你别怂 2024-07-15 07:22:31

有几个新的实用程序封装了“gdb 方法”并添加了一些额外的内容。我现在使用的叫做“reptyr”（“Re-PTY-er”）。除了获取 STDERR/STDOUT 之外，它实际上还会更改进程的控制终端（即使它之前没有附加到终端）。

最好的用途是启动一个 screen 会话，并使用它将正在运行的进程重新附加到 screen 内的终端，以便您可以安全地与其分离并稍后返回。

它打包在流行的发行版上（例如：“apt-get install reptyr”）。

http://onethingwell.org/post/2924103615/reptyr

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夜未央樱花落 2024-07-15 07:22:31

GDB 方法似乎更好，但您也可以使用 strace 来完成此操作：

$ strace -p <PID> -e write=1 -s 1024 -o file

通过 strace 的手册页：

   -e write=set
               Perform a full hexadecimal and ASCII dump of all the
               data written to file descriptors listed in the spec-
               ified  set.  For example, to see all output activity
               on file descriptors 3 and 5 use -e write=3,5.   Note
               that  this is independent from the normal tracing of
               the write(2) system call which is controlled by  the
               option -e trace=write.

这会打印出比您需要的更多的内容（十六进制部分），但你可以通过 sed 轻松解决这个问题。

GDB method seems better, but you can do this with strace, too:

$ strace -p <PID> -e write=1 -s 1024 -o file

Via the man page for strace:

   -e write=set
               Perform a full hexadecimal and ASCII dump of all the
               data written to file descriptors listed in the spec-
               ified  set.  For example, to see all output activity
               on file descriptors 3 and 5 use -e write=3,5.   Note
               that  this is independent from the normal tracing of
               the write(2) system call which is controlled by  the
               option -e trace=write.

This prints out somewhat more than you need (the hexadecimal part), but you can sed that out easily.

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流年已逝 2024-07-15 07:22:31

我不确定它是否适合您，但我不久前读过一页描述使用 gdb 的方法

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猥︴琐丶欲为 2024-07-15 07:22:31

我使用 strace 并将十六进制输出解码为明文：

PID=some_process_id
sudo strace -f -e trace=write -e verbose=none -e write=1,2 -q -p $PID -o "| grep '^ |' | cut -c11-60 | sed -e 's/ //g' | xxd -r -p"

我将此命令与其他答案结合起来。

I used strace and de-coded the hex output to clear text:

PID=some_process_id
sudo strace -f -e trace=write -e verbose=none -e write=1,2 -q -p $PID -o "| grep '^ |' | cut -c11-60 | sed -e 's/ //g' | xxd -r -p"

I combined this command from other answers.

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烟燃烟灭 2024-07-15 07:22:31

仅使用 -ewrite（而不是 =1 后缀），strace 的输出要少得多。而且它比 GDB 方法简单一点，IMO。

我用它来查看现有 MythTV 编码作业的进度（sudo 因为我不拥有编码过程）：

$ ps -aef | grep -i handbrake
mythtv   25089 25085 99 16:01 ?        00:53:43 /usr/bin/HandBrakeCLI -i /var/lib/mythtv/recordings/1061_20111230122900.mpg -o /var/lib/mythtv/recordings/1061_20111230122900.mp4 -e x264 -b 1500 -E faac -B 256 -R 48 -w 720
jward    25293 20229  0 16:30 pts/1    00:00:00 grep --color=auto -i handbr

$ sudo strace -ewrite -p 25089
Process 25089 attached - interrupt to quit
write(1, "\rEncoding: task 1 of 1, 70.75 % "..., 73) = 73
write(1, "\rEncoding: task 1 of 1, 70.76 % "..., 73) = 73
write(1, "\rEncoding: task 1 of 1, 70.77 % "..., 73) = 73
write(1, "\rEncoding: task 1 of 1, 70.78 % "..., 73) = 73^C

strace outputs a lot less with just -ewrite (and not the =1 suffix). And it's a bit simpler than the GDB method, IMO.

I used it to see the progress of an existing MythTV encoding job (sudo because I don't own the encoding process):

$ ps -aef | grep -i handbrake
mythtv   25089 25085 99 16:01 ?        00:53:43 /usr/bin/HandBrakeCLI -i /var/lib/mythtv/recordings/1061_20111230122900.mpg -o /var/lib/mythtv/recordings/1061_20111230122900.mp4 -e x264 -b 1500 -E faac -B 256 -R 48 -w 720
jward    25293 20229  0 16:30 pts/1    00:00:00 grep --color=auto -i handbr

$ sudo strace -ewrite -p 25089
Process 25089 attached - interrupt to quit
write(1, "\rEncoding: task 1 of 1, 70.75 % "..., 73) = 73
write(1, "\rEncoding: task 1 of 1, 70.76 % "..., 73) = 73
write(1, "\rEncoding: task 1 of 1, 70.77 % "..., 73) = 73
write(1, "\rEncoding: task 1 of 1, 70.78 % "..., 73) = 73^C

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