varFolders script for https://michael-herbst.com/linux-ssds-and-disk-encryption.html

varFolders

#!/bin/bash
### BEGIN INIT INFO
# Provides: varFolders
# Required-Start:    $local_fs
# Required-Stop:     $local_fs
# Default-Start:     1 2 3 4 5
# Default-Stop:      0 6
# Short-Description: Backup and restore var folder structures
### END INIT INFO
#
# Script Version 1.0 (14/09/2013)
#
##################################################################################
# Licence:
#
# (C) 2013 Michael F. Herbst <info@michael-herbst.com>
#
# This script is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# 
# It is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# A copy of the GNU General Public License can be found 
# at <http://www.gnu.org/licenses/>.
#
##################################################################################
# Usage:
#
# run with "stop" to create a tar archive representing the  structure of a sub-
# directory of var. This means that no actual files, only symbolic links and
# folders are kept. Run with "start" to restore this structure back to the original
# location.
#
# The idea is that this allows write-intensive subfolders of var (eg. log, spool .. )
# to be mounted as ramdisks using tmpfs in a SSD-only system to reduce the amounts
# of writes the SSD suffers. 
#
# DIRS are the subfolers of var which are subject to this treatment. With the 
# KEEPFILES the user can control if only the structure or everything should be 
# stored. (Eg. if something is debugged and files should be kept across power cyles)
# 
# The script also checks for presence of /etc/var_folders_keep_files. If this file
# is present the script will automatically set KEEPFILES="y".
#
# If KEEPFILES="n" the archive will only be updated if the names of the subfolders /
# links have changed or if subfolders / links have been created / deleted. Other 
# changes (eg permission changes, owner changes, ...) won't trigger an update
# automatically. You can however force an update at the next invocation of "stop"
# by calling varFolders with the option "force-update".
#
##################################################################################
# Settings:

KEEPFILES="n"			#Keep the files or only the folder structure?
DIRS="log spool"		#dirs under /var to extract folder structure/files from
ARFILE="var_folders.tar"	#Archive to keep stuff in (stored under /var/local)

##################################################################################

. /lib/lsb/init-functions
set -e
PATH=/sbin:/bin:/usr/sbin:/usr/bin
PROG=varFolders

initialise(){
	#set DIRS, DIR1 and KEEPFILES

	local DTMP=
	for DIR in $DIRS; do
		if [ "$DIR" == "local" ]; then
			echo "Can't store the directory structure of /var/local!"
			exit 1
		fi
		[ -z "$DIR1" ] && DIR1="$DIR"   #The first valid dir
		[ -d "/var/$DIR" ] && DTMP="$DTMP $DIR"
	done
	DIRS="$DTMP"
	if [ -z "$DIRS" ]; then
		echo "No valid directory in DIRS"
		exit 1
	fi

	#We go to /var
	cd /var
	mkdir -p /var/local

	[ -e /etc/var_folders_keep_files ] && KEEPFILES="y"
	true
}

update_archive() {
	if [ "$KEEPFILES" == "y" ]; then
		update_archive_keepfiles
		return $?
	fi
	update_archive_normal
	return $?
}

update_archive_keepfiles() {
	#Create tar with all files
	tar cf /var/local/"$ARFILE" $DIRS
	chmod 640 /var/local/"$ARFILE"
	find $DIRS -type d -o -type l > /var/local/"$ARFILE".list
}

update_archive_normal() {
	TMP=`mktemp`
	find $DIRS -type d -o -type l > "$TMP"

	SUMNEW=`cat "$TMP" | sha512sum`
	SUMOLD=
	[ -f /var/local/"$ARFILE".list ] && SUMOLD=`cat /var/local/"$ARFILE".list | sha512sum`

	if [[ "$SUMOLD" == "$SUMNEW" ]]; then
		rm "$TMP"
		return
	fi

	mv "$TMP" /var/local/"$ARFILE".list
	tar cf /var/local/"$ARFILE"  --no-recursion `cat /var/local/"$ARFILE".list`
	chmod 640 /var/local/"$ARFILE"
}

force_update() {
	#removing the list file will force the update if stop is called
	rm -f "/var/local/${ARFILE}.list"
}

extract_archive() {
	[ ! -f /var/local/"$ARFILE" ] && return 1

	#Archive has already been extracted:
	[ -f /var/${DIR1}/archive_extracted ] && return 0

	#Extract:
	tar xf /var/local/"$ARFILE"
	touch /var/${DIR1}/archive_extracted
}

##################################################################################

case $1 in
	start)
		log_begin_msg "Starting $PROG"
		if ! initialise; then
			log_end_msg 1
			exit 1
		fi
		if ! extract_archive; then
			log_end_msg 1
			exit 1
		fi
		log_end_msg 0
	;;
	stop)
		log_begin_msg "Stopping $PROG"
		if ! initialise; then
			log_end_msg 1
			exit 1
		fi
		if ! update_archive; then
			log_end_msg 1
			exit 1
		fi
		log_end_msg 0
	;;
	force-update)
		initialise || exit 1
		force_update
		exit $RET
	;;	
	restart|force-reload|status)
		exit 0
	;;
	*)
		echo "Usage: $0 {start|stop|restart|force-reload|force-update|status}" >&2
		exit 1
	;;
esac

exit 0