Applications may use a single subdirectory under
/usr/lib. If an application uses a subdirectory,
all architecture-dependent data exclusively used by the application
must be placed within that subdirectory.
architecture-independent application-specific static files and
subdirectories must be placed in
 See below, in the
section, for a discussion of
/usr/libexec for executable binaries.
 For example, the
perl5 subdirectory for
Perl 5 modules and libraries.
Some executable commands such as makewhatis and
sendmail have also been traditionally placed in
/usr/lib. makewhatis is an
internal binary and must be placed in a binary directory; users access
only catman. Newer sendmail
binaries are now placed by default in
Additionally, systems using a sendmail-compatible
mail transfer agent must provide /usr/sbin/sendmail
as the sendmail command, either as the executable
itself or as a symlink to the appropriate executable.
Host-specific data for the X Window System must not be stored in
/usr/lib/X11. Host-specific configuration files
xorg.conf must be stored in
/etc/X11. This includes configuration data such
system.twmrc even if it is only made a
symbolic link to a more global configuration file (probably in