ldconfig

Update symlinks and rebuild the cache (usually run when a new library is installed)

Update the symlinks for a given directory
Print the libraries in the cache and check whether a given library is present

ldconfig [-v] [-p] [-n] [-N] [-X] [-f conf] [-C cache] [-r root] [directory ...]

-v, --verbose
    Print actions performed, like creating links or adding cache entries.

-p, --print-cache
    Display contents of current ld.so.cache without updating.

-n
    Process directories but do not create symbolic links.

-N
    Do not canonicalize paths or update ld.so.cache.

-X
    Do not generate links for libraries (only update cache).

-f conf
    Use alternate config file instead of /etc/ld.so.conf.

-C cache
    Write cache to specified file instead of /etc/ld.so.cache.

-r root
    Set root directory for operations (chroots).

directory ...
    Scan these directories for libraries, appending to config.

ldconfig is a key Linux utility for managing the dynamic linker's runtime bindings. It scans directories listed in /etc/ld.so.conf and /etc/ld.so.conf.d/ files to locate shared object libraries (.so files). The tool then:

• Creates symbolic links for libraries with sonames to their actual files.
• Generates or updates the cache file /etc/ld.so.cache, enabling fast lookups by the dynamic linker (ld.so).

This cache avoids scanning library directories at every program launch, improving performance.

Invoked automatically by package managers (e.g., after rpm or dpkg installs), or manually by root when adding libraries to new directories. Without arguments, it processes the default config. Specifying directories overrides or appends to the config.

Common use: After copying libs to /usr/local/lib, run ldconfig to integrate them system-wide. Verbose mode aids debugging library paths.

Essential for 32/64-bit multi-arch systems, handling hardware capabilities (hwcap) directories like /lib64. Misuse risks system breakage if cache corrupts.

Requires root privileges (or CAP_SYS_ADMIN) to update cache/links. Errors in config can prevent programs from finding libraries, breaking applications. Always backup /etc/ld.so.cache before manual runs. Not for static linking.

ldconfig -p | grep libc -- List libc libraries.
echo '/opt/mylib' >> /etc/ld.so.conf && ldconfig -- Add directory.

Handles /lib/i386-linux-gnu/, /lib/x86_64-linux-gnu/; use dpkg --add-architecture for cross-arch setups.

Developed as part of GNU C library (glibc) in early 1990s for Linux ELF dynamic linking support. Evolved with multi-arch (i386/x86_64) and hwcap features in glibc 2.0+. Standard in all major distros since kernel 2.x era.

ldd(1), ld.so(8), ld(1), ldconfig(8)