Linux sets dynamic library paths and environment variables

After installing source compiled libraries on Linux, we need to enable the system to recognize them by default.

Assume that we have installed the library under the path /usr/local/aarch64_qt5.12.0:

1. Set the dynamic library link configuration

If dynamic library link configuration is not performed, the system will not be able to find the required *.so file, causing the software to fail to execute.

You can view dependencies by executing the ldd command, for example:

pi@NanoPi-NEO-Plus2:~$ ldd untitled
        linux-vdso.so.1 =>  (0x0000ffffba839000)
        libQt5Widgets.so.5 => not found
        libQt5Gui.so.5 => not found
        libQt5Core.so.5 => not found
        libpthread.so.0 => /lib/aarch64-linux-gnu/libpthread.so.0 (0x0000ffffba7e2000)
        libstdc++.so.6 => /usr/lib/aarch64-linux-gnu/libstdc++.so.6 (0x0000ffffba653000)
        libm.so.6 => /lib/aarch64-linux-gnu/libm.so.6 (0x0000ffffba5a6000)
        libgcc_s.so.1 => /lib/aarch64-linux-gnu/libgcc_s.so.1 (0x0000ffffba585000)
        libc.so.6 => /lib/aarch64-linux-gnu/libc.so.6 (0x0000ffffba43e000)
        /lib/ld-linux-aarch64.so.1 (0x0000ffffba80e000)

The stupidest way is to copy the compiled corresponding so to /usr/lib or /lib. If there are many corresponding so, it will be a problem.

Setting method:

1) Create the dynamic library configuration file *.conf under the /etc/ld.so.conf.d path, for example:

sudo vim /etc/ld.so.conf.d/Qt5.conf

Add to the file:

/usr/local/aarch64_qt5.12.0/lib

2) Load dynamic library configuration

Execute command: sudo ldconfig

pi@NanoPi-NEO-Plus2:~$ ldd untitled
        linux-vdso.so.1 =>  (0x0000ffffa4b1a000)
        libQt5Widgets.so.5 => /usr/local/aarch64_qt5.12.0/lib/libQt5Widgets.so.5 (0x0000ffffa451d000)
        libQt5Gui.so.5 => /usr/local/aarch64_qt5.12.0/lib/libQt5Gui.so.5 (0x0000ffffa4039000)
        libQt5Core.so.5 => /usr/local/aarch64_qt5.12.0/lib/libQt5Core.so.5 (0x0000ffffa39ed000)
        libpthread.so.0 => /lib/aarch64-linux-gnu/libpthread.so.0 (0x0000ffffa39c1000)
        libstdc++.so.6 => /usr/lib/aarch64-linux-gnu/libstdc++.so.6 (0x0000ffffa3832000)
        libm.so.6 => /lib/aarch64-linux-gnu/libm.so.6 (0x0000ffffa3785000)
        libgcc_s.so.1 => /lib/aarch64-linux-gnu/libgcc_s.so.1 (0x0000ffffa3764000)
        libc.so.6 => /lib/aarch64-linux-gnu/libc.so.6 (0x0000ffffa361d000)
        libdl.so.2 => /lib/aarch64-linux-gnu/libdl.so.2 (0x0000ffffa360a000)
        /lib/ld-linux-aarch64.so.1 (0x0000ffffa4aef000)

2. Set environment variables

When executing related programs, you do not need to switch to the specified directory to execute, and can be executed in any directory.

Setting method:

1. The current session takes effect temporarily: command line input export PATH=$PATH:/usr/local/aarch64_qt5.12.0/bin

2. Permanently valid for users: vi ~/.bashrc The last line input export PATH=$PATH:/usr/local/aarch64_qt5.12.0/bin

Make environment variables effective: source .bashrc

3. Global and permanent effect:

Add a path to $PATH in /etc/profile or /etc/bash.bashrc. If the names are the same, you need to put the new path in front of other paths.

export PATH=$PATH:/usr/local/aarch64_qt5.12.0/bin

Enable environment variables to take effect: source /etc/profile

pi@NanoPi-NEO-Plus2:~$ echo $PATH
/usr/local/aarch64_qt5.12.0/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/

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