Chapter 9. The Operating System

62

created and removed by the

postinst

and

prerm

maintainer scripts and not be included in

the

.deb

archive. These scripts must not fail if either of these operations fail.

For example, the

emacsen common

package could contain something like

if [ !  e /usr/local/share/emacs ]

then

if mkdir /usr/local/share/emacs 2>/dev/null

then

chown root:staff /usr/local/share/emacs

chmod 2775 /usr/local/share/emacs

fi

fi

in its

postinst

script, and

rmdir /usr/local/share/emacs/site lisp 2>/dev/null || true

rmdir /usr/local/share/emacs 2>/dev/null || true

in the

prerm

script. (Note that this form is used to ensure that if the script is interrupted, the

directory

/usr/local/share/emacs

will still be removed.)

If you do create a directory in

/usr/local

for local additions to a package, you should ensure

that settings in

/usr/local

take precedence over the equivalents in

/usr

.

However, because

/usr/local

and its contents are for exclusive use of the local administra 

tor, a package must not rely on the presence or absence of files or directories in

/usr/local

for normal operation.

The

/usr/local

directory itself and all the subdirectories created by the package should

(by default) have permissions 2775 (group writable and set group id) and be owned by

root.staff

.

9.1.3 The system wide mail directory

The system wide mail directory is

/var/mail

. This directory is part of the base system and

should not owned by any particular mail agents. The use of the old location

/var/spool

/mail

is deprecated, even though the spool may still be physically located there. To maintain

partial upgrade compatibility for systems which have

/var/spool/mail

as their physical

mail spool, packages using

/var/mail

must depend on either

libc6

(>= 2.1.3 13), or on

base files

(>= 2.2.0), or on later versions of either one of these packages.

9.2 Users and groups

9.2.1 Introduction

The Debian system can be configured to use either plain or shadow passwords.