Answer by Patric for What is the LD_PRELOAD trick?

As many people mentioned, using LD_PRELOAD to preload library. By the way, you can CHECK if the setting is available by ldd command.

Example: Suppose you need to preload your own libselinux.so.1.

> ldd /bin/ls    ...    libselinux.so.1 => /lib/x86_64-linux-gnu/libselinux.so.1 (0x00007f3927b1d000)    libacl.so.1 => /lib/x86_64-linux-gnu/libacl.so.1 (0x00007f3927914000)    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f392754f000)    libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007f3927311000)    libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f392710c000)    /lib64/ld-linux-x86-64.so.2 (0x00007f3927d65000)    libattr.so.1 => /lib/x86_64-linux-gnu/libattr.so.1 (0x00007f3926f07000)

Thus, set your preload environment:

export LD_PRELOAD=/home/patric/libselinux.so.1

Check your library again:

>ldd /bin/ls    ...    libselinux.so.1 =>    /home/patric/libselinux.so.1 (0x00007fb9245d8000)    ...