bash Linux 程序的外部禁用信号
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Externally disabling signals for a Linux program
提问by Harry
On Linux, is it possible to somehow disable signaling for programs externally... that is, without modifying their source code?
在 Linux 上，是否有可能以某种方式禁用外部程序的信号……也就是说，不修改它们的源代码？
Context:
语境：
I'm calling a C (and also a Java) program from within a bash script on Linux. I don't want any interruptions for my bash script, and for the other programs that the script launches (as foreground processes).
我正在从 Linux 上的 bash 脚本中调用 C（以及 Java）程序。我不希望我的 bash 脚本和脚本启动的其他程序（作为前台进程）受到任何干扰。
While I can use a...
虽然我可以使用...
trap '' INT
... in my bash script to disable the Ctrl C signal, this works only when the program control happens to be in the bash code. That is, if I press Ctrl C while the C program is running, the C program gets interrupted and it exits! This C program is doing some critical operation because of which I don't want it be interrupted. I don't have access to the source code of this C program, so signal handling inside the C program is out of question.
...在我的 bash 脚本中禁用 Ctrl C 信号，这仅在程序控制恰好在 bash 代码中时才有效。也就是说，如果我在 C 程序运行时按下 Ctrl C，C 程序会被中断并退出！这个 C 程序正在执行一些关键操作，因此我不希望它被中断。我无权访问这个 C 程序的源代码，因此 C 程序内部的信号处理是不可能的。
#!/bin/bash
trap 'echo You pressed Ctrl C' INT
# A C program to emulate a real-world, long-running program,
# which I don't want to be interrupted, and for which I
# don't have the source code!
#
# File: y.c
# To build: gcc -o y y.c
#
# #include <stdio.h>
# int main(int argc, char *argv[]) {
# printf("Performing a critical operation...\n");
# for(;;); // Do nothing forever.
# printf("Performing a critical operation... done.\n");
# }
./y
Regards,
问候，
/HS
/HS
回答by caf
The process signal mask is inherited across exec, so you can simply write a small wrapper program that blocks SIGINTand executes the target:
进程信号掩码是跨 继承的exec，因此您可以简单地编写一个小包装程序来阻止SIGINT和执行目标：
#include <signal.h>
#include <unistd.h>
#include <stdio.h>
int main(int argc, char *argv[])
{
sigset_t sigs;
sigemptyset(&sigs);
sigaddset(&sigs, SIGINT);
sigprocmask(SIG_BLOCK, &sigs, 0);
if (argc > 1) {
execvp(argv[1], argv + 1);
perror("execv");
} else {
fprintf(stderr, "Usage: %s <command> [args...]\n", argv[0]);
}
return 1;
}
If you compile this program to noint, you would just execute ./noint ./y.
如果将此程序编译为noint，则只需执行./noint ./y。
As ephemient notes in comments, the signal disposition is also inherited, so you can have the wrapper ignore the signal instead of blocking it:
正如注释中的附注，信号处置也是继承的，因此您可以让包装器忽略信号而不是阻止它：
#include <signal.h>
#include <unistd.h>
#include <stdio.h>
int main(int argc, char *argv[])
{
struct sigaction sa = { 0 };
sa.sa_handler = SIG_IGN;
sigaction(SIGINT, &sa, 0);
if (argc > 1) {
execvp(argv[1], argv + 1);
perror("execv");
} else {
fprintf(stderr, "Usage: %s <command> [args...]\n", argv[0]);
}
return 1;
}
(and of course for a belt-and-braces approach, you could do both).
（当然，对于腰带和大括号方法，您可以两者都做）。
回答by J-16 SDiZ
The "trap" command is local to this process, never applies to children.
“trap”命令是这个进程的本地命令，从不应用于子进程。
To really trap the signal, you have to hack it using a LD_PRELOADhook. This is non-trival task (you have to compile a loadable with _init(), sigaction()inside), so I won't include the full code here. You can find an example for SIGSEGV on Phack Volume 0x0b, Issue 0x3a, Phile #0x03.
要真正捕获信号，您必须使用LD_PRELOAD钩子对其进行破解。这是一项非常重要的任务（您必须使用_init(), sigaction()inside编译可加载项），因此我不会在此处包含完整代码。您可以在Phack Volume 0x0b, Issue 0x3a, Phile #0x03上找到 SIGSEGV 的示例。
Alternativlly, try the nohupand tailtrick.
或者，尝试nohup和tail技巧。
nohup your_command &
tail -F nohup.out
回答by richo
I would suggest that your C (and Java) application needs rewriting so that it can handle an exception, what happens if it really does need to be interrupted, power fails, etc...
我建议您的 C（和 Java）应用程序需要重写，以便它可以处理异常，如果它确实需要被中断，电源故障等会发生什么......
I that fails, J-16 is right on the money. Does the user need to interract with the process, or just see the output (do they even need to see the output?)
我失败了，J-16 是对的。用户是否需要与流程交互，或者只需要查看输出（他们甚至需要查看输出吗？）
回答by calandoa
The solutions explained above are not working for me, even by chaining the both commands proposed by Caf.
上面解释的解决方案对我不起作用，即使链接 Caf 提出的两个命令也是如此。
However, I finally succeeded in getting the expected behavior this way :
但是，我最终以这种方式成功获得了预期的行为：
#!/bin/zsh
setopt MONITOR
TRAPINT() { print AAA }
print 1
( ./child & ; wait)
print 2
If I press Ctrl-C while childis running, it will wait that it exits, then will print AAA and 2. childwill not receive any signals.
如果我在child运行时按 Ctrl-C ，它将等待退出，然后打印 AAA 并且 2.child不会收到任何信号。
The subshell is used to prevent the PID from being shown.
子外壳用于防止显示 PID。
And sorry... this is for zsh though the question is for bash, but I do not know bash enough to provide an equivalent script.
抱歉……这是针对 zsh 的，尽管问题是针对 bash 的，但我对 bash 的了解不足以提供等效的脚本。
回答by lama12345
This is example code of enabling signals like Ctrl+C for programs which block it.
这是为阻止它的程序启用 Ctrl+C 等信号的示例代码。
fixControlC.c
fixControlC.c
#include <stdio.h>
#include <signal.h>
int sigaddset(sigset_t *set, int signo) {
printf("int sigaddset(sigset_t *set=%p, int signo=%d)\n", set, signo);
return 0;
}
Compile it:
编译它：
gcc -fPIC -shared -o fixControlC.so fixControlC.c
Run it:
运行：
LD_LIBRARY_PATH=. LD_PRELOAD=fixControlC.so mysqld
