Multiple glibc libraries on a single host

Question

Multiple glibc libraries on a single host

My linux (SLES-8) server currently has glibc-2.2.5-235, but I have a program which won\'t work on this version and requires

Answer 1

First of all, the most important dependency of each dynamically linked program is the linker. All so libraries must match the version of the linker.

Let's take simple exaple: I have the newset ubuntu system where I run some program (in my case it is D compiler - ldc2). I'd like to run it on the old CentOS, but because of the older glibc library it is impossible. I got

ldc2-1.5.0-linux-x86_64/bin/ldc2: /lib64/libc.so.6: version `GLIBC_2.15' not found (required by ldc2-1.5.0-linux-x86_64/bin/ldc2)
ldc2-1.5.0-linux-x86_64/bin/ldc2: /lib64/libc.so.6: version `GLIBC_2.14' not found (required by ldc2-1.5.0-linux-x86_64/bin/ldc2)

I have to copy all dependencies from ubuntu to centos. The proper method is following:

First, let's check all dependencies:

ldd ldc2-1.5.0-linux-x86_64/bin/ldc2 
    linux-vdso.so.1 =>  (0x00007ffebad3f000)
    librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f965f597000)
    libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f965f378000)
    libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f965f15b000)
    libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f965ef57000)
    libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f965ec01000)
    libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f965e9ea000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f965e60a000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f965f79f000)

linux-vdso.so.1 is not a real library and we don't have to care about it.

/lib64/ld-linux-x86-64.so.2 is the linker, which is used by the linux do link the executable with all dynamic libraries.

Rest of the files are real libraries and all of them together with the linker must be copied somewhere in the centos.

Let's assume all the libraries and linker are in "/mylibs" directory.

ld-linux-x86-64.so.2 - as I've already said - is the linker. It's not dynamic library but static executable. You can run it and see that it even have some parameters, eg --library-path (I'll return to it).

On the linux, dynamically linked program may be lunched just by its name, eg

/bin/ldc2

Linux loads such program into RAM, and checks which linker is set for it. Usually, on 64-bit system, it is /lib64/ld-linux-x86-64.so.2 (in your filesystem it is symbolic link to the real executable). Then linux runs the linker and it loads dynamic libraries.

You can also change this a little and do such trick:

/mylibs/ld-linux-x86-64.so.2 /bin/ldc2

It is the method for forcing the linux to use specific linker.

And now we can return to the mentioned earlier parameter --library-path

/mylibs/ld-linux-x86-64.so.2 --library-path /mylibs /bin/ldc2

It will run ldc2 and load dynamic libraries from /mylibs.

This is the method to call the executable with choosen (not system default) libraries.