[mamikk]

There are a lot of small utilities which are built upon LD_PRELOAD, for example.

- fakeroot: Gives the running program the impression that it is running as root, often used for example for building debian packages. This will let the build script create a directory tree which it believes is owned by root and then when that directory tree is packed by tar, tar will also see root as the owner and the .tar-archive will have root as the user/group for the files in the final debian package.

- faketime: Gives the running program the impression that it is running at some specific time. Usefull for testing code during specific events like leap-years, etc.

- eatmydata: Will ignore all fsync() and related system calls which ensures files are written to permanent storage. I have used this once for running a database during a testsuite, and databases are much faster when they do not have to wait for the data to reach permanent storage.

[sltkr]

My favorite tool that (ab)uses LD_PRELOAD to do something useful is `stdbuf`: https://linux.die.net/man/1/stdbuf

The implementation is completely bonkers. The tool sets some environmental variables, then spawns a child process with LD_PRELOAD set to load a library (libstdbuf.so) which has a some initialization code that runs when the library is loaded, and that based on the environmental variables, calls setvbuf() from inside the child process to override the buffering behavior.

[a-dub]

tsocks: route all network traffic through a socks gateway with elegant per-process controls. (i guess a proxychains ancestor?)

[Fnoord]

faketime could've been used to circumvent time bombs in software. This could for example allow you eternal trial access. Nowadays stuff just requires networking with internet connection though.

You could also use LD_PRELOAD to get a different MAC address. This would've work with FlexLM.

Though its probably easier with a bit of hexediting or disassembling to modify the binary personally, I get fuzzy feelings of love from the type of software cracking which does not require modified binaries.

[snarg]

libnaw uses it to wrap and authenticate connect() and accept() calls.

frida uses it to wrap and inject... anything.

These programs have all been around for quite a long time. I think libnaw has been around since early 2000s at least.