Ldd

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

Example

<source>

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)    
        [...]

</source> 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: <source>

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)

</source>

Usage

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

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

</source>

Saving example

<source> 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.4.4.3 /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:~ # </source>

See also

• strace
• nm
• ldd's man page
• http://unix.stackexchange.com/questions/171632/where-will-the-system-search-for-dynamic-libraries