Why do I have libc.so.6 under /usr/lib/x86_64-linux-gnu directory?

Question

Why do I have libc.so.6 under /usr/lib/x86_64-linux-gnu directory?

After I read this question difference between libc6-dev and libc6 , I started a fresh Ubuntu 20.04 LTS VPS and went checking what files are included in some Ubuntu packages.

I checked libc6-dev (https://packages.ubuntu.com/focal/amd64/libc6-dev/filelist) and libc6 (https://packages.ubuntu.com/focal/amd64/libc6/filelist).

As we can see, the libc6-dev have those share libraries under /usr/lib/x86_64-linux-gnu/ and libc6 ‘s share libraries are under /lib/x86_64-linux-gnu/.

But what makes me curious is that:

I also have libc.so.6 under /usr/lib/x86_64-linux-gnu/ (libc.so.6 -> libc-2.31.so*). And apt install remove libc6-dev doesn’t remove libc.so.6. Where does this libc.so.6 come from?
The -rw-r--r-- 1 root root 298 Apr 7 09:24 libc.so installed by libc6-dev packge is only 298 bytes, what? Why?

sudo apt list --installed output: https://pastebin.com/geDjY2z2
ll -h | grep libc output: https://pastebin.com/UHn5QVt1

ll -h | grep libc output, left(remove libc6-dev):

Asked By: Rick

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Source

Answer 1

libc.so.6 is part of the libc6 package. It is only in the file list in /lib/x86_64-linux-gnu, but /lib is a symlink to /usr/lib, so it shows up in /usr/lib/x86_64-linux-gnu as well. libc.so.6 is the library which programs using the C library refer to:

$ ldd /bin/true
    linux-vdso.so.1 (0x00007ffc797a9000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fc865f4a000)
    /lib64/ld-linux-x86-64.so.2 (0x00007fc86614b000)

libc.so is used when building programs, and is a linker script rather than a library; you can examine its contents:

$ cat /lib/x86_64-linux-gnu/libc.so
/* GNU ld script
   Use the shared library, but some functions are only in
   the static library, so try that secondarily.  */
OUTPUT_FORMAT(elf64-x86-64)
GROUP ( /lib/x86_64-linux-gnu/libc.so.6 /usr/lib/x86_64-linux-gnu/libc_nonshared.a  AS_NEEDED ( /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 ) )

Answered By: Stephen Kitt