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docs/system/backup-reminders.md

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+Display a reminder when it's been more than N days since a backup
+=================================================================
+
+Backups are important, regular ones doubly so. Unfortunately it's very easy to forget to make regular backups. Since Qubes stores the date and time when a VM was backed up, we will use this information to remind the user (probably you) when it has been more than N days since a backup.
+
+Architecture
+------------
+
+We create a shell script that:
+- compiles the list of VMs which we care about ensuring regular backups for,
+- determines the oldest backup timestamp for those VMs,
+- checks how far that timestamp is in the past, and
+- if that timestamp is older than a threshold, pops up a notification in dom0.
+
+We use an "exclude file" to exclude some VMs which we don't backup, and therefore for which we should not check timestamps for.
+
+Since we're probably running on a laptop, we run the script daily using `anacron` instead of `cron`, since `anacron` will deal with situtions when the machine is frequently in "suspend" mode. (Which laptops are)
+
+We set up an anacrontab for our user (as opposed to using a system-wide one) and run `anacron` hourly using the user's `crontab`. This gives some minor security benefits (by not running things as root) and reduces the chance of accidentally causing problems in the system through misconfiguration.
+
+
+Implementation
+--------------
+
+#### Excludes file ####
+
+A plain text file containing the names of VMs which are not backed up. In this example, we save it in dom0, `/home/${USER}/backup/exclude_vms.txt`:
+```
+fedora-30
+whonix-gw-15
+whonix-ws-15
+```
+(you'll need to change as needed depending on your backup policy)
+
+#### Backup script ####
+
+Put this in dom0, probably in `/home/${USER}/backup/remind.sh`:
+```
+#!/bin/bash
+
+# Remind if this many days since backup
+DAYS_THRESHOLD=3
+
+# Setup variables
+BACKUP_DIR="/home/${USER}/backup"
+EXCLUDE_FILE=${BACKUP_DIR}/exclude_vms.txt
+
+
+# Build backup VM list
+ALL_VMS=(`/usr/bin/qvm-ls --raw-list`)
+EXCLUDE_VMS=(`/usr/bin/cat $EXCLUDE_FILE`)
+EXCLUDE_VMS+=("dom0")
+BACKUP_VMS=()
+for i in "${ALL_VMS[@]}"; do
+        skip=
+        for j in "${EXCLUDE_VMS[@]}"; do
+                [[ $i == $j ]] && { skip=1; break; }
+        done
+        [[ -n $skip ]] || BACKUP_VMS+=("$i")
+done
+
+# Get oldest known backup TS
+TS=`/usr/bin/date +%s`
+echo "TS now: $TS"
+for vm in "${BACKUP_VMS[@]}"; do
+        vm_ts=`/usr/bin/qvm-prefs --get $vm backup_timestamp`
+        
+        if [ "$vm_ts" -lt "$TS" ]; then
+                echo "New oldest TS: $vm_ts"
+                TS=$vm_ts
+        fi
+done
+
+# Get delta between current time and oldest backup
+NOW=`/usr/bin/date +%s`
+DELTA=`/usr/bin/expr $NOW - $TS`
+DELTA_DAYS=`/usr/bin/expr $DELTA / 86400`
+echo "delta in seconds: $DELTA / days: $DELTA_DAYS"
+if [ "$DELTA_DAYS" -gt "$DAYS_THRESHOLD" ]; then
+        /usr/bin/notify-send --expire-time 86400000 "It has been $DELTA_DAYS days since last backup"
+fi
+
+echo `/usr/bin/date` >> $BACKUP_DIR/reminders.log
+remind.sh (END)
+```
+
+Then mark it as executable with `chmod +x /home/${USER}/backup/remind.sh`.
+
+You can try running it right away to see how long it's been since your last backup.
+
+
+#### Anacrontab ####
+
+Anacron should be installed by default in dom0, but you can check it by running (in dom0): `dnf info cronie-anacron` and verifying the first line of the info is "Installed Packages".
+
+First some basic configuration:
+1. Make sure we have a .config directory: `mkdir -p ~/.config`
+1. Create an anacrontab file for your user: `touch ~/.config/anacrontab`
+1. Make sure we have a ~/.var/spool/anacron directory: `mkdir -p ~/.var/spool/anacron/`
+
+Now open up the file `${HOME}/.config/anacrontab` in your text editor of choice and add to it the following, replacing USERNAME_GOES_HERE with the dom0 user account name (to find it, `echo ${USER}`:
+```
+# /etc/anacrontab: configuration file for anacron
+
+# See anacron(8) and anacrontab(5) for details.
+
+SHELL=/bin/sh
+PATH=/sbin:/bin:/usr/sbin:/usr/bin
+MAILTO=USERNAME_GOES_HERE
+# the maximal random delay added to the base delay of the jobs
+RANDOM_DELAY=45
+# the jobs will be started during the following hours only
+START_HOURS_RANGE=3-22
+
+#period in days   delay in minutes   job-identifier   command
+@daily 0        backup-reminder /home/USERNAME_GOES_HERE/backup/remind.sh
+```
+
+#### Crontab ####
+
+Finally, add the following to your crontab file, accessed by running `crontab -e`: (`crontab -e` is the only way you should access your crontab)
+
+```
+@hourly /usr/sbin/anacron -t ${HOME}/.config/anacrontab -S ${HOME}/.var/spool/anacron
+```