When php uses system () to enable firefox in linux, the following Error occurs: Error: nodisplayspecified. how can this problem be solved?

When php uses system () to enable firefox in linux, the following Error occurs: Error: nodisplayspecified. could you please help me ?, Is there operation permission? What about code ?, Browser access and terminal access are two permissions. The general user permission is in the browser. you can install sudo # on the machine to query the sudo version apt-cac. the following Error occurs when php uses system () to enable firefox in linux: Error: no display specified.
Could you please help me?

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Is there operation permission?

What about code?
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Browser access and terminal access are two permissions. General user permissions in the browser. you have sudo installed on the host.
# Querying sudo versions
Apt-cache search sudo
# Install sudo
Apt-get install sudo
Then: system ("sudo firefox http://www.baidu.com"); // switch to root permission

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Discussion

All the code is as follows:
$ Cmd = "sudo firefox -- saveimage http://baidu.com ";
System ($ cmd, $ str );
Echo $ str;
What I want to achieve is to enable firefox to save the entire webpage as an image