How to find out which libraries a certain software such as php-fpm depends on?

Most of them can be found through ldd, but some others are unknown.

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Most of them can be found through ldd, but some others are unknown.

ldd php-fpm is to view the shared libraries that static binary files depend on.
You can use sudo lsof -p PID to view the files opened when the program is running, including dependent shared libraries.
It should be noted that some do not PHP extensions compiled into PHP-FPM (also so files) sometimes depend on other libraries, so you have to find out which libraries PHP-FPM depends on. It is best to load all the PECL extensions you use and run them with lsof to view.
If you want to package a PHP binary package that can be decompressed and used across Linux, you can read this article of mine.
The Android version of PHP I compiled by myself is completely statically linked with dependent libraries.