Find Shared Libraries for a Binary with ldd on Linux

The ldd utility lists dynamic dependencies, basically the shared libraries needed to make a binary file work. It is the first thing to check when a program refuses to start with an error such as error while loading shared libraries: libfoo.so.1: cannot open shared object file. Here’s the basic syntax:

ldd /path/to/binary

Prerequisites

ldd is part of glibc (the glibc-common or glibc package on CentOS/RHEL), so it is already installed.
Root is not required to read most binaries; this example logs in and uses root.

1. Change to a bin directory

Root prompt on the server named screen, changing to /sbin to run ldd

Change to /sbin, or some other bin directory:

cd /sbin

Running cd /sbin to change to a system binary directory

2. Run ldd on the binary

If you do an ldd {binary name} it will return what its dependencies are:

ldd mkfs

ldd mkfs output listing linux-vdso.so.1, libc.so.6 and ld-linux-x86-64.so.2

That’s it!

Reading the output

Each line is one library the binary is linked against:

libc.so.6 => /lib64/libc.so.6 (0x...): the library name the binary asks for, the file the dynamic linker found for it, and the address it was loaded at.
linux-vdso.so.1: a virtual library the kernel provides in memory, so it has no file path.
/lib64/ld-linux-x86-64.so.2: the dynamic linker itself.
libsomething.so.1 => not found: the library the program is missing. This is the line you are looking for when a program will not start.

For a statically linked binary or a shell script, ldd prints not a dynamic executable.

Fixing a “not found” library

Find the package that ships the missing file, then install it:

yum provides '*/libsomething.so.1'
yum install packagename

If the library is already on disk somewhere the linker does not search, such as /usr/local/lib or /opt/app/lib, add that directory to a file in /etc/ld.so.conf.d/ and rebuild the linker cache:

echo /opt/app/lib > /etc/ld.so.conf.d/app.conf
ldconfig
ldconfig -p | grep libsomething

For a quick one-off test you can instead set LD_LIBRARY_PATH=/opt/app/lib before the command.

Untrusted binaries: use objdump instead

The ldd man page warns that ldd may run the program in some cases, so never point it at a binary you do not trust. To list the libraries a file asks for without running anything, read the ELF header:

objdump -p ./binary | grep NEEDED
readelf -d ./binary | grep NEEDED

These list what the binary asks for but do not resolve the paths.

RHEL, AlmaLinux and Rocky Linux 9 and 10

ldd works exactly the same. Since RHEL 7, /sbin is a symlink to /usr/sbin (and /lib64 to /usr/lib64), so you may see /usr/lib64 paths in the output. Use dnf provides '*/libsomething.so.1' to find the package for a missing library.

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find shared libraries for binary ldd