Inspect shared library dependencies with ldd and
verify how the dynamic linker resolves libraries at runtime.
Make /opt/mylib discoverable via
/etc/ld.so.conf.d and ldconfig, then
validate the cache and test a temporary override with
LD_LIBRARY_PATH.
A vendor shipped a binary that depends on a custom shared
library. The library was dropped under /opt/mylib
and the binary now fails to start because the dynamic linker
cannot find it. You need to prove what the binary needs, make
the new path discoverable, refresh the loader cache, and
validate resolution with a controlled, repeatable workflow.
Treat this as a dependency triage task. Confirm the missing
object, verify the search path and cache state, then apply a
minimal persistent fix via
/etc/ld.so.conf.d. Use
LD_LIBRARY_PATH only for testing or containment.
ldd.
ldconfig -p.
/etc/ld.so.conf includes snippet
files under /etc/ld.so.conf.d.
/opt/mylib to the loader search path using a
dedicated snippet file.
ldconfig and
validate the new directory is scanned.
LD_LIBRARY_PATH as a temporary, per-shell
override.
ldd to surface
missing objects (not found).
/etc/ld.so.conf and
/etc/ld.so.conf.d/*.conf.
ldconfig and ldconfig -p.
LD_LIBRARY_PATH for scoped testing.
ldd /bin/ls
This prints loader resolution results: which libraries are
required and what paths they map to. When a dependency
cannot be resolved, you will typically see
not found.
# Example pattern:
# libselinux.so.1 => /lib64/libselinux.so.1 (0x00007f...)
# libdoesnotexist.so => not foundldconfig -p | head
ldconfig -p
prints what is currently known in
ld.so.cache. If a library directory is not
configured, its objects will not appear here.
ld.so.conf is wired.
grep -E '^[^#]' /etc/ld.so.conf
Most systems include drop-in snippet files via
/etc/ld.so.conf.d/*.conf. That is the preferred
place to add custom library paths without editing the
top-level file directly.
ls -1 /etc/ld.so.conf.dThese files define additional search directories. Keep your change isolated in a single, clearly named snippet so it is easy to audit and roll back.
/opt/mylib via a new snippet file.
echo /opt/mylib | sudo tee /etc/ld.so.conf.d/mylib.conf
This only writes configuration. The loader cache will not
change until you run ldconfig.
sudo ldconfig
ldconfig
scans configured directories and rebuilds
ld.so.cache. This is the step that makes the
new directory effective system-wide.
ldconfig scanned the new directory.
sudo ldconfig -v 2>/dev/null | grep -m1 /opt/mylibThis is a quick sanity check. If the directory does not appear, the snippet was not read or the file contents are invalid.
LD_LIBRARY_PATH as a temporary override.
export LD_LIBRARY_PATH=/opt/mylib:$LD_LIBRARY_PATH
This prepends /opt/mylib for processes launched
from the current shell. It does not modify system
configuration and will not persist across sessions.
Services started by systemd will not inherit this unless explicitly configured in the unit or environment file. Use this for validation, not as a long-term deployment strategy.
The library is missing, the path is not configured, or the
SONAME does not match what the binary requests. Confirm the
library exists under /opt/mylib, then rebuild
the cache with ldconfig.
The snippet must contain a valid directory path on its own
line. Also confirm /etc/ld.so.conf includes
/etc/ld.so.conf.d/*.conf.
That is expected. It only affects the current shell’s process tree. If a service needs it for testing, define the environment in the systemd unit or an environment file.
Adding directories changes how multiple binaries resolve
libraries. Keep paths narrow, prefer dedicated directories,
and revalidate the target binary with ldd after
changes.
If you created a snippet under /etc/ld.so.conf.d,
remove it and rebuild the cache to revert the system-wide
search path.
sudo rm -f /etc/ld.so.conf.d/mylib.conf
sudo ldconfig
ldconfig -p | grep -m1 /opt/mylib || true
ldconfig -v
no longer lists /opt/mylib, and the cache output
does not surface libraries from that directory.
ldd <binary>
: Shows runtime shared library dependencies for an ELF
binary.
ldconfig -p
: Displays the current dynamic linker cache contents.
grep -E '^[^#]' /etc/ld.so.conf
: Displays active (non-comment) loader configuration lines.
ls -1 /etc/ld.so.conf.d
: Lists drop-in snippet files used by the loader
configuration.
/etc/ld.so.conf.d/*.conf
: Directory of snippet files that add search paths.
echo <dir> | sudo tee /etc/ld.so.conf.d/<name>.conf
: Writes a new search path snippet for the dynamic linker.
tee
: Writes to a root-owned file while still accepting
stdin from a pipeline.
ldconfig
: Rebuilds the dynamic linker cache based on configured
directories.
ldconfig -v
: Shows verbose scan output (useful for proving a directory
is read).
-v
: Enables verbose scanning output.
LD_LIBRARY_PATH=<dir>:<existing>
: Temporarily prepends directories to the library search path
for a process tree.