The /lib directory contains kernel modules and those shared library images (the C programming code library) needed to boot the system and run the commands in the root filesystem, ie. by binaries in /bin and /sbin. Libraries are readily identifiable through their filename extension of *.so. Windows equivalent to a shared library would be a DLL (dynamically linked library) file. They are essential for basic system functionality. Kernel modules (drivers) are in the subdirectory /lib/modules/'kernel-version'. To ensure proper module compilation you should ensure that /lib/modules/'kernel-version'/kernel/build points to /usr/src/'kernel-version' or ensure that the Makefile knows where the kernel source itself are located. /lib/'machine-architecture' Contains platform/architecture dependent libraries. /lib/iptables iptables shared library files. /lib/kbd Contains various keymaps. /lib/modules/'kernel-version' The home of all the kernel modules. The organisation of files here is reasonably clear so no requires no elaboration. /lib/modules/'kernel-version'/isapnpmap.dep has details on ISA based cards, the modules that they require and various other attributes. /lib/modules/'kernel-version'/modules.dep lists all modules dependencies. This file can be updated using the depmod command. /lib/modules/'kernel-version'/pcimap is the PCI equivalent of the /lib/modules/'kernel-version'/isapnpmap.dep file. /lib/modules/'kernel-version'/usbmap is the USB equivalent of the /lib/modules/'kernel-version'/isapnpmap.dep file. /lib/oss All OSS (Open Sound System) files are installed here by default. /lib/security PAM library files. The FSSTND requires that shared libraries that are only necessary for binaries in /usr (such as any X Window binaries) must not be in /lib. Only the shared libraries required to run binaries in /bin and /sbin may be here. In particular, the library libm.so.* may also be placed in /usr/lib if it is not required by anything in /bin or /sbin. At least one of each of the following filename patterns are required (they may be files, or symbolic links): libc.so.* The dynamically-linked C library (optional) ld* The execution time linker/loader (optional) If a C preprocessor is installed, /lib/cpp must be a reference to it, for historical reasons. The usual placement of this binary is /usr/lib/gcc-lib/<target>/<version>/cpp. /lib/cpp can either point at this binary, or at any other reference to this binary which exists in the filesystem. (For example, /usr/bin/cpp is also often used.) The following directories, or symbolic links to directories, must be in /lib, if the corresponding subsystem is installed: /lib -- essential shared libraries and kernel modules /lib/modules Loadable kernel modules (optional) /lib<qual> : Alternate format essential shared libraries (optional) There may be one or more variants of the /lib directory on systems which support more than one binary format requiring separate libraries. This is commonly used for 64-bit or 32-bit support on systems which support multiple binary formats, but require libraries of the same name. In this case, /lib32 and /lib64 might be the library directories, and /lib a symlink to one of them. If one or more of these directories exist, the requirements for their contents are the same as the normal /lib directory, except that /lib<qual>/cpp is not required. /lib<qual>/cpp is still permitted: this allows the case where /lib and /lib<qual> are the same (one is a symbolic link to the other).