Specifying multiple files with LD_PRELOAD

Question

I know how to override one library with LD_PRELOAD, for example, as follows.

LD_PRELOAD=./getpid.so ./testpid

Now my question is how to override multiple files. Say I want to override both getpid and getid, how would I specify that?

score 88 · Answer 1 · edited Mar 31 '20 at 13:14

88

According to the ld.so manpage, it is a space separated list. So:

LD_PRELOAD="path1 path2"

ought to work.

edited Mar 31 '20 at 13:14

peterh

answered Dec 12 '11 at 12:57

William Pursell

19

According to the man-page colons are also accepted, e.g.: `LD_PRELOAD=path1:path2` – Isac Casapu Dec 28 '16 at 13:20
4

Interesting. In the section on LD_LIBRARY_PATH, the page mentions that semi-colons and colons are valid, but makes no mention of spaces. The parsing of $ORIGIN, $LIB, and $PLATFORM are (I believe) new. Spaces were always a bit surprising, and I find it odd that they are valid in LD_PRELOAD but not LD_LIBRARY_PATH. – William Pursell Dec 28 '16 at 13:45
4

Note that the page dated 2001 (from https://www.kernel.org/pub/linux/docs/man-pages/Archive/man-pages-2.00.tar.bz2) states: " LD_PRELOAD: A whitespace-separated list of additional, user-specified, ELF shared libraries to be loaded before all others." I cannot find a change in binutils, and would be curious to know if this is merely an omission in the documentation or if the behavior has changed recently. – William Pursell Dec 28 '16 at 14:02
Since it is spaces, if libraries to preload have a space in their pathname it will break, right? – Golar Ramblar Jul 27 '23 at 18:35
@MetallicPriest, I think this solution solves this question, can you check and maybe mark it as the solution? – Golar Ramblar Jul 27 '23 at 18:36
@WilliamPursell, the [manpage linked in the answer](http://kernel.org/doc/man-pages/online/pages/man8/ld.so.8.html) states "*separated by spaces or colons*". To complete your answer, I suggest to add also the option with spaces. – Golar Ramblar Jul 27 '23 at 18:39

score 5 · Answer 2 · answered Dec 12 '11 at 12:35

5

One option is to have the overridden version of both getpid and getid in a single .so which you give to LD_PRELOAD.

answered Dec 12 '11 at 12:35

codaddict

hmm, interesting! Will try that! – MetallicPriest Dec 12 '11 at 12:37
its nice to make a single library that holds all the functions you want, a bit more simple to do. this answer is nicest, though others are more correct. – user7296055 Dec 04 '17 at 10:17

2 Answers2