The /tmp directory must be made available
for programs that require temporary files.
Programs must not assume that any files or directories in
/tmp are preserved between invocations of the
program.
IEEE standard POSIX.1-2008 lists requirements similar to the above section.
Although data stored in /tmp may be deleted
in a site-specific manner, it is recommended that files and
directories located in /tmp be deleted whenever
the system is booted.
FHS added this recommendation on the basis of historical precedent and common practice, but did not make it a requirement because system administration is not within the scope of this standard.