Lots of libraries can't be found

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1

I was just

‘strace ls’

as you do…

on Nixos 20.03… .

However , the command works fine, but it’s seems to be missing a lof of libraries.

The are not specified in ‘ldd ls’

Is this just dark magic of nixos linker or something else.

execve("/run/current-system/sw/bin/ls", ["ls"], 0x7ffff782e390 /* 72 vars */) = 0
brk(NULL)                               = 0x11a1000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f916de5b000
access("/etc/ld-nix.so.preload", R_OK)  = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/nix/store/rq9vqzjqay8fz8qdidmbgs3lqpq0y6zb-acl-2.2.53/lib/tls/x86_64/x86_64/librt.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/nix/store/rq9vqzjqay8fz8qdidmbgs3lqpq0y6zb-acl-2.2.53/lib/tls/x86_64/x86_64", 0x7ffc2f7b43f0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/nix/store/rq9vqzjqay8fz8qdidmbgs3lqpq0y6zb-acl-2.2.53/lib/tls/x86_64/librt.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/nix/store/rq9vqzjqay8fz8qdidmbgs3lqpq0y6zb-acl-2.2.53/lib/tls/x86_64", 0x7ffc2f7b43f0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/nix/store/rq9vqzjqay8fz8qdidmbgs3lqpq0y6zb-acl-2.2.53/lib/tls/x86_64/librt.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)

ldd shows

ldd /run/current-system/sw/bin/ls
        linux-vdso.so.1 (0x00007ffc2f6e6000)
        librt.so.1 => /nix/store/xg6ilb9g9zhi2zg1dpi4zcp288rhnvns-glibc-2.30/lib/librt.so.1 (0x00007ff403554000)
        libacl.so.1 => /nix/store/rq9vqzjqay8fz8qdidmbgs3lqpq0y6zb-acl-2.2.53/lib/libacl.so.1 (0x00007ff403549000)
        libattr.so.1 => /nix/store/b3yikpnxly8vgr2c0sspwqckx44hb474-attr-2.4.48/lib/libattr.so.1 (0x00007ff403541000)
        libcrypto.so.1.1 => /nix/store/hysf4ll023i4q51hymgcqzxik4inq8gm-openssl-1.1.1g/lib/libcrypto.so.1.1 (0x00007ff403255000)
        libpthread.so.0 => /nix/store/xg6ilb9g9zhi2zg1dpi4zcp288rhnvns-glibc-2.30/lib/libpthread.so.0 (0x00007ff403234000)
        libc.so.6 => /nix/store/xg6ilb9g9zhi2zg1dpi4zcp288rhnvns-glibc-2.30/lib/libc.so.6 (0x00007ff403073000)
        libdl.so.2 => /nix/store/xg6ilb9g9zhi2zg1dpi4zcp288rhnvns-glibc-2.30/lib/libdl.so.2 (0x00007ff40306e000)
        /nix/store/xg6ilb9g9zhi2zg1dpi4zcp288rhnvns-glibc-2.30/lib/ld-linux-x86-64.so.2 => /nix/store/xg6ilb9g9zhi2zg1dpi4zcp288rhnvns-glibc-2.30/lib64/ld-linux-x86-64.so.2 (0x00007ff403560000)

These seems to be there, is it just some danging dependcies? or libraries that are trying to load other libraries that don’t exist?

2

This is normal.

ELF records these libraries in DT_NEEDED entries, containing the name of the library, e.g. librt.so.1. Then there is DT_RUNPATH entry listing the paths where to search for the libraries:

$ readelf -d result/bin/ls | grep RUNPATH
 0x000000000000001d (RUNPATH)            Library runpath: [/nix/store/camix5721pydww6zwwd4wg77krk61gf1-acl-2.2.53/lib:/nix/store/3y5s6iyzqg2rwy8qz79i5f6cfmwqiaav-attr-2.4.48/lib:/nix/store/3wa1xwnfv8ada1za1r8m4vmsiz1jifqq-glibc-2.32-35/lib]

The path will be searched in order until the needed libraries are discovered, hence the many misses.

On regular Linux distributions, there are only few paths to look for (e.g. /usr/lib) so the rpath is typically empty but for Nix, we need to use rpath to make the packages self-contained. Alternative would be just stuffing absolute paths to DT_NEEDED entries.

1 Like
3

Thanks for a quick reply and a explanation of this behaviour.