Loader

• Program Library HOWTO

ld.so/ld-linux.so

• ld.so handles a.out binaries
• ld-linux.so* handles ELF
  • /lib/ld-linux.so.1 for libc5
  • /lib/ld-linux.so.2 for glibc2
• ld-uClibc.so

search path

1. LD_LIBRARY_PATH
   • A colon-separated list of directories in which to search for ELF libraries at execution-time
   • Why LD_LIBRARY_PATH is bad
   • LD_LIBRARY_PATH is not the answer
   • (COMMAND LINE OPTIONS)—library-path PATH
     • Override LD_LIBRARY_PATH environment variable
2. /etc/ld.so.conf
   • File containing a list of colon, space, tab, newline, or comma-separated directories in which to search for libraries.
3. default paths
   1. /usr/lib
   2. /lib
      • libraries required for startup

cache

• ldconfig
  • reads in the file /etc/ld.so.conf
  • sets up the appropriate symbolic links in the dynamic link directories (so they'll follow the standard conventions)
  • writes a cache to /etc/ld.so.cache

• /etc/ld.so.cache
  • a compiled list of directories in which to search for libraries and an ordered list of candidate libraries
  • File containing an ordered list of libraries found in the directories specified in /etc/ld.so.conf.
  • On start-up, then, the dynamic loader actually uses the file /etc/ld.so.cache and then loads the libraries it needs.

dependencies

• ldd
  • print shared library dependencies