Linux ldd command (list dependencies)

The ldd command in Linux - List Dynamic Dependencies - provides a list of the dynamic dependencies that a given program needs. It will return the name of the shared library and its expected location on the disk.

Examples:

$ ldd /bin/bash
libreadline.so.4 => /lib/libreadline.so.4 (0x4001c000)
libhistory.so.4 => /lib/libhistory.so.4 (0x40049000)
libncurses.so.5 => /lib/libncurses.so.5 (0x40050000)
libdl.so.2 => /lib/libdl.so.2 (0x40096000)
libc.so.6 => /lib/libc.so.6 (0x40099000)
/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)

In this example, the bash program needs all of these libraries to work.

The ldd command is important in determining which libraries are required for an executable.

When an error occurs during the execution of a program, complaining about the lack of an incorrect library or version, the ldd program can be used to determine which library and the version of it must be installed for the correct functioning of the program.

The program that configures the directories containing the shared libraries is ldconfig.

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