This file is indexed.

postinst is in passwd 1:4.1.5.1-1ubuntu9.

This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.

The actual contents of the file can be viewed below.

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#!/bin/sh -e

case "$1" in
configure)
    # Fix permissions on various log files from old versions of the debian
    # installer, some unrelated to passwd but we decided to put the fix
    # here since there was no better place. This can safely be removed
    # after etch is released.
    if dpkg --compare-versions "$2" lt "1:4.0.14-9"; then
	    for log in /var/log/base-config* \
		    $(find /var/log/debian-installer/ /var/log/installer/ -type f 2>/dev/null ); do
		if [ -e "$log" ]; then
			chmod 600 "$log"
		fi
            done
    fi

    rm -f /etc/pam.d/passwd.pre-upgrade 2>/dev/null
	if ! getent group shadow | grep -q '^shadow:[^:]*:42'
	then
		groupadd -g 42 shadow || (
    			cat <<EOF
Group ID 42 has been allocated for the shadow group.  You have either
used 42 yourself or created a shadow group with a different ID.
Please correct this problem and reconfigure with ``dpkg --configure passwd''.

Note that both user and group IDs in the range 0-99 are globally
allocated by the Debian project and must be the same on every Debian
system.
EOF
    			exit 1
		)
	fi
    ;;
esac

# Run shadowconfig only on new installs
[ -z "$2" ] && shadowconfig on



exit 0