如何重定向一个已经运行的进程的输出 [英] How to redirect output of an already running process

问题描述

通常我会这样开始

longcommand &;

我知道你可以做这样的事情。

I know you can redirect it by doing something like

longcommand > /dev/null;

例如摆脱输出或

longcommand 2>&1 > output.log

捕捉输出。

但我有时会忘记，并想知道是否有捕获或事后重定向的一种方式。

But I sometimes forget, and was wondering if there is a way to capture or redirect after the fact.

longcommand
ctrl-z
bg 2>&1 > /dev/null

或类似的东西，这样我就可以继续使用终端没有消息在终端上弹出。

or something like that so I can continue using the terminal without messages popping up on the terminal.

推荐答案

请参阅的从正在运行的进程重定向输出

See Redirecting Output from a Running Process.

首先，我运行命令猫＆GT; foo1 在一个会话并测试从标准输入的数据被复制到文件中。然后在另一个会议上，我重定向输出。

Firstly I run the command cat > foo1 in one session and test that data from stdin is copied to the file. Then in another session I redirect the output.

首先查找进程的PID：

Firstly find the PID of the process:

$ ps aux | grep cat
rjc 6760 0.0 0.0 1580 376 pts/5 S+ 15:31 0:00 cat

现在检查该文件处理它有开放的：

Now check the file handles it has open:

$ ls -l /proc/6760/fd
total 3
lrwx—— 1 rjc rjc 64 Feb 27 15:32 0 -> /dev/pts/5
l-wx—— 1 rjc rjc 64 Feb 27 15:32 1 -> /tmp/foo1
lrwx—— 1 rjc rjc 64 Feb 27 15:32 2 -> /dev/pts/5

现在运行GDB：

$ gdb -p 6760 /bin/cat
GNU gdb 6.4.90-debian

[license stuff snipped]

Attaching to program: /bin/cat, process 6760

[snip other stuff that's not interesting now]

(gdb) p close(1)
$1 = 0
(gdb) p creat("/tmp/foo3″, 0600)
$2 = 1
(gdb) q
The program is running. Quit anyway (and detach it)? (y or n) y
Detaching from program: /bin/cat, process 6760

在GDB的 P 命令将打印一个前pression，价值的前pression可以调用一个函数，它可以是一个系统调用...所以，我执行的close（）系统调用，并通过文件句柄1，那么我执行科瑞（）系统调用来打开一个新的文件。在科瑞（）的结果是1，这意味着它取代了previous文件句柄。如果我想使用相同的文件输出和错误，或者如果我想更换一些其他数字文件句柄然后我会需要调用 dup2（）系统调用取得这一结果。

The p command in GDB will print the value of an expression, an expression can be a function to call, it can be a system call… So I execute a close() system call and pass file handle 1, then I execute a creat() system call to open a new file. The result of the creat() was 1 which means that it replaced the previous file handle. If I wanted to use the same file for stdout and stderr or if I wanted to replace a file handle with some other number then I would need to call the dup2() system call to achieve that result.

在这个例子中我选择使用科瑞（）而不是的open（）因为有较少的参数。为标志的C宏是不可用的，从GDB（它不使用C头文件），所以我将不得不读取头文件发现这一点 - 它并不难做到，但是这样会花费更多的时间。需要注意的是0600是为业主有读/写访问和组和其他无访问权限的八进制。它也将努力对以后的文件，该参数和运行chmod使用0。

For this example I chose to use creat() instead of open() because there are fewer parameter. The C macros for the flags are not usable from GDB (it doesn’t use C headers) so I would have to read header files to discover this – it’s not that hard to do so but would take more time. Note that 0600 is the octal permission for the owner having read/write access and the group and others having no access. It would also work to use 0 for that parameter and run chmod on the file later on.

这之后，我对结果进行验证：

After that I verify the result:

ls -l /proc/6760/fd/
total 3
lrwx—— 1 rjc rjc 64 2008-02-27 15:32 0 -> /dev/pts/5
l-wx—— 1 rjc rjc 64 2008-02-27 15:32 1 -> /tmp/foo3 <====
lrwx—— 1 rjc rjc 64 2008-02-27 15:32 2 -> /dev/pts/5

  
  

键入更多的数据，以猫结果的文件中的/ tmp / foo3 追加到

如果您想要关闭您需要关闭所有文件句柄它，打开一个新的设备，可以控制tty，然后调用原始会话 setsid（）。

If you want to close the original session you need to close all file handles for it, open a new device that can be the controlling tty, and then call setsid().

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