`sudo` 附加到具有 root 权限的文件(在 C 中的 `system(3)` 中) [英] `sudo` to append to file with root permissions (inside `system(3)` from C)

问题描述

我正在尝试使用 sudo 写入 /etc 中的文件，该文件只能由 root 从非特权 C 内部写入程序.

I am attempting to use sudo to write to a file in /etc that is writable only by root, from inside an unprivileged C program.

system("sudo /bin/sh -c 'echo 'iface wlan0 inet dhcp' >> /etc/network/interfaces'");

这似乎没有失败，但文件未修改.怎么了?

This doesn't appear to fail, but the file is unmodified. What is wrong?

推荐答案

按照您所拥有的结构，重定向在 sudo 操作之外进行评估，因此不会有root权限，不能打开/etc/network/interfaces进行写入.你需要这样做:

Structured as you have it, the redirection is evaluated outside the sudo operation, and therefore does not have root privileges and cannot open /etc/network/interfaces for writing. You need to do it like this instead:

system("sudo /bin/sh -c \"echo 'iface wlan0 inet dhcp' >> /etc/network/interfaces\"");

这样重定向就由 shell inside sudo 来评估.

so that the redirection is evaluated by the shell inside the sudo.

(另外，单引号内不能嵌套单引号.)

(Also, you can't nest single quotes inside single quotes.)

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