Ldd

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ldd is a command that shows which libraries are used by an executable file.

Example
itchy:~ # ldd /usr/local/bin/ktimetracker 
        linux-vdso.so.1 =>  (0x00007fffdb7ff000)
        libkutils.so.4 => /usr/local/lib64/libkutils.so.4 (0x00007feed334b000)
        libkparts.so.4 => /usr/local/lib64/libkparts.so.4 (0x00007feed30fa000)
        libkcal.so.4 => /usr/local/lib64/libkcal.so.4 (0x00007feed2dd7000)    
        [...]

In this case, libkutils is loaded from /usr/local/lib64/libkutils.so.4 to memory address 0x00007feed334b000.

ldd uses the LD_LIBRARY_PATH variable to find out where to search for libraries:

tweedleburg:~/jail # ldd ktimetracker 
        linux-vdso.so.1 =>  (0x00007fffa7dff000)
        libkutils.so.4 => /usr/lib64/libkutils.so.4 (0x00007fa69f8e1000)
        libkparts.so.4 => /usr/lib64/libkparts.so.4 (0x00007fa69f69f000)
tweedleburg:~/jail # export LD_LIBRARY_PATH=.
tweedleburg:~/jail # ldd ktimetracker 
        linux-vdso.so.1 =>  (0x00007fff65fff000)
        libkutils.so.4 => ./libkutils.so.4 (0x00007f595da82000)
        libkparts.so.4 => ./libkparts.so.4 (0x00007f595d831000)

Usage

To find out all files that an executable file depends on:

ldd /usr/local/bin/ktimetracker | sed "s/^.* => //" | sed "s/ (0x.*//"

Saving example

tweedleburg:~ # ldd /usr/bin/skype 
        linux-gate.so.1 =>  (0xffffe000)      
        libasound.so.2 => /usr/lib/libasound.so.2 (0xf7ea0000)
        libXv.so.1 => /usr/lib/libXv.so.1 (0xf7e9a000)        
        libXss.so.1 => /usr/lib/libXss.so.1 (0xf7e96000)      
        librt.so.1 => /lib/librt.so.1 (0xf7e8c000)            
        libQtDBus.so.4 => not found                           
        libQtGui.so.4 => not found                            
        libQtNetwork.so.4 => not found                        
        libQtCore.so.4 => not found                           
        libpthread.so.0 => /lib/libpthread.so.0 (0xf7e71000)  
        libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0xf7d7c000)
        libm.so.6 => /lib/libm.so.6 (0xf7d53000)              
        libgcc_s.so.1 => /lib/libgcc_s.so.1 (0xf7d44000)      
        libc.so.6 => /lib/libc.so.6 (0xf7be8000)              
        libX11.so.6 => /usr/lib/libX11.so.6 (0xf7ab5000)      
        libXext.so.6 => /usr/lib/libXext.so.6 (0xf7aa4000)    
        libdl.so.2 => /lib/libdl.so.2 (0xf7a9e000)            
        /lib/ld-linux.so.2 (0xf7f99000)                       
        libxcb-xlib.so.0 => /usr/lib/libxcb-xlib.so.0 (0xf7a9b000)
        libxcb.so.1 => /usr/lib/libxcb.so.1 (0xf7a7d000)          
        libXau.so.6 => /usr/lib/libXau.so.6 (0xf7a79000)          
tweedleburg:~ # ll /usr/lib/libQtDBus.so.4
lrwxrwxrwx 1 root root 18 Jun 16 18:41 /usr/lib/libQtDBus.so.4 -> libQtDBus.so.4.5.0
tweedleburg:~ # rm /usr/lib/libQtDBus.so.4
tweedleburg:~ # ln -s /usr/lib/libQtDBus.so.4.
libQtDBus.so.4.4          libQtDBus.so.4.4.3        libQtDBus.so.4.5          libQtDBus.so.4.5.0        libQtDBus.so.4.5.0.debug
tweedleburg:~ # ln -s /usr/lib/libQtDBus.so.4.4.3 /usr/lib/libQtDBus.so.4
tweedleburg:~ # ldd /usr/bin/skype
        linux-gate.so.1 =>  (0xffffe000)
        libasound.so.2 => /usr/lib/libasound.so.2 (0xf7ea6000)
        libXv.so.1 => /usr/lib/libXv.so.1 (0xf7ea0000)
        libXss.so.1 => /usr/lib/libXss.so.1 (0xf7e9c000)
        librt.so.1 => /lib/librt.so.1 (0xf7e92000)
        libQtDBus.so.4 => /usr/lib/libQtDBus.so.4 (0xf7e28000)
        libQtGui.so.4 => not found
        libQtNetwork.so.4 => not found
        libQtCore.so.4 => not found
        libpthread.so.0 => /lib/libpthread.so.0 (0xf7e0e000)
        libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0xf7d19000)
        libm.so.6 => /lib/libm.so.6 (0xf7cf0000)
        libgcc_s.so.1 => /lib/libgcc_s.so.1 (0xf7ce1000)
        libc.so.6 => /lib/libc.so.6 (0xf7b85000)
        libX11.so.6 => /usr/lib/libX11.so.6 (0xf7a52000)
        libXext.so.6 => /usr/lib/libXext.so.6 (0xf7a41000)
        libdl.so.2 => /lib/libdl.so.2 (0xf7a3b000)
        /lib/ld-linux.so.2 (0xf7f9f000)
        libdbus-1.so.3 => /lib/libdbus-1.so.3 (0xf79f9000)
        libQtXml.so.4 => not found
        libQtCore.so.4 => not found
        libz.so.1 => /lib/libz.so.1 (0xf79e4000)
        libgthread-2.0.so.0 => /usr/lib/libgthread-2.0.so.0 (0xf79dd000)
        libglib-2.0.so.0 => /usr/lib/libglib-2.0.so.0 (0xf7918000)
        libxcb-xlib.so.0 => /usr/lib/libxcb-xlib.so.0 (0xf7915000)
        libxcb.so.1 => /usr/lib/libxcb.so.1 (0xf78f7000)
        libXau.so.6 => /usr/lib/libXau.so.6 (0xf78f3000)
        libpcre.so.0 => /usr/lib/libpcre.so.0 (0xf78bf000)
tweedleburg:~ #

See also