backups.md (14249B)
1 ---
2 author: "JayVii"
3 title: "Encrypted Backup via rsync"
4 date: "2023-04-07"
5 description: "How I create atomic encrypted backups via gocryptfs and rsync"
6 tags: ["backup", "encryption", "tech"]
7 ---
8
9 > **Update 2024-04-28:**
10 >
11 > The resulting script from this blog post can be found on my git page:
12 > [rsync_encrypted_backup](https://src.jayvii.de/pub/rsync_encrypted_backup/)
13
14 Backups have been somewhat of a pain for me for quite a while, as I could never
15 find a suitable, easy to manage and easy to recover option for my private
16 computer.
17
18 My goal was to create a simple off-site backup routine (i.e. "the cloud"), which
19 would be easy to recover from, suitably fast - ideally with atomic/delta
20 updates - and reasonably secure, i.e. strong default encryption like
21 AES256-level.
22
23 I tried several options like `7z` with encryption and low (or no) compression
24 rate, sending a whole ZIP archive to a remote storage or even updating existing
25 archives. However, this of course turned out to be rather cumbersome, prone to
26 write-errors / connection issues and extremely slow.
27
28 The next approach did work reasonably well, and is what I want to present here.
29 I am sure there is still room for improvement, so if you have any suggestions,
30 feel free to send me a DM in the Fediverse or an e-mail.
31
32 The well-known `rsync` tool is a natural candidate for atomic backups in the
33 Linux-world. It can sync directories with all sort of remote end-points,
34 including (S)FTP, WebDAV, etc. It keeps ACLs, modes and ownership of files
35 intact and is relatively fast, light on system resources and can do syncing both
36 ways (i.e. it may also be used to restore your files). However, `rsync` does not
37 support encryption while syncing your files.
38
39 So in order to encrypt backups within `rsync`, they have to be encrypted
40 **before** transmission, ideally in real-time and without impacting read-speed
41 all that much.
42
43 ## File Encryption
44
45 A close to perfect solution for this task is `gocryptfs`, the spiritual
46 successor of `encryptfs`. It is an encrypted overlay-file-system, that
47 (crucially) supports "reverse-mode", is extremely fast and utilizes strong
48 encryption methods.
49
50 What this means exactly in the context of backups is, that we can mount
51 the directory we want to back up (e.g. our home-directory) in an encrypted,
52 real-time updated form, and sync the encrypted versions of all files rather than
53 the original unencrypted versions. The aforementioned "reverse-mode" is useful,
54 because it mounts a pre-existing, unencrypted directory as encrypted volume.
55
56 So first, let's start with creating a setup for the encrypted file-system. This
57 has to be done only once and creates the metadata and encryption heads for the
58 volume. Once this is done, we only need to mount the encrypted volume in the
59 future:
60
61 ```{.sh}
62 #!/usr/bin/env bash
63
64 gocryptfs \
65 --init \ # initilise the volume
66 --reverse \ # use "reverse mode"
67 --plaintextnames \ # do not obfuscate names of files and directories
68 "$HOME" # target directory. Here: our home-folder
69 ```
70
71 This process will ask you to set an encryption passphrase as well as provide you
72 with a master restore key. **BACK THIS KEY UP SOMEWHERE SAFE AND IN SEVERAL
73 PLACES, BOTH DIGITALLY AS WELL AS PHYSICALLY!**
74
75 The metadata file will be stored in your unencrypted directory as
76 `.gocryptfs.reverse.conf` and in the encrypted storage as `gocryptfs.conf`
77 (unencrypted). Make sure to store this somewhere secure too, as it is required
78 to decrypt the storage in case you need to restore your backups.
79
80 From now on, we may mount the directory in its encrypted from:
81
82 ```{.sh}
83 #!/usr/bin/env bash
84
85 # create temporary directory as encrypted mountpoint
86 ENCRYPTED_DIR=$(mktemp -d)
87
88 # mount home-directory to newly created mountpoint
89 gocryptfs \
90 --ro \ # mount in read-only mode
91 --reverse \ # use "reverse mode"
92 "$HOME" \ # unencrypted directory to be backed up
93 "$ENCRYPTED_DIR" && # temporary mount point
94 echo "$HOME has been mounted in encrypted form to $ENCRYPTED_DIR" ||
95 echo "Mounting $HOME to $ENCRYPTED_DIR failed!"
96 ```
97
98 In your encrypted directory, you will now find your entire home-directory in
99 encrypted form. The reason we used `--plaintextnames` before was, that it makes
100 the recovery process a lot easier, if you can actually identify the files and
101 folders from their names (ofc. their contents are encrypted). If you do not need
102 this feature, because you'd recover the entire directory, rather than only
103 partials of it, you may consider removing that parameter when creating the
104 volume.
105
106 The `--ro` parameter sets read-only permissions for the encrypted mount, meaning
107 that you can not write new files to the encrypted volume. Importantly, writing
108 to the unencrypted directory is still possible. Doing so will also update the
109 encrypted directory in real-time. The parameter may protect our directory from
110 technical or user mistakes, however, i.e. if we by accident use the reverse
111 order of target and source in `rsync`...
112
113 If we want to recover a backup later-on, of course we do need to write
114 permissions in the encrypted volume. This is mentioned later in this blog post
115 again.
116
117 ## File Transmission
118
119 Next, we can finally back up our encrypted directory via `rsync`. Let's first
120 talk about the parameters that might be useful for backups. Personally, I want
121 to exclude several directories in the backup, like the "Downloads", ".cache" and
122 similar folders. `rsync` can even use wild-cards here, so you can exclude every
123 `.git` folder or specific file-types (if they have the appropriate file-ending).
124 This is of course not possible (or a lot harder...) if you skipped the
125 `--plaintextnames` when creating the encrypted volume, as all file- and
126 directory names are obfuscated without it.
127
128 We want to keep file-permissions and file-owners, so the `--archive` parameter
129 is handy here. Since we want to see what is happening during the procedure, the
130 `--verbose` and `--progress` parameters are useful as well. Additionally, files
131 that we have deleted from our system should also disappear from the backup, next
132 time we sync them up. Ideally, this should happen *after* new files are
133 transferred via the `--delete-delay`.
134
135 Because I back up multiple devices to the same network storage, it is a good
136 idea to name the target folder after the hostname of the device. Furthermore,
137 even though I do atomic backups, I want to keep several versions of my
138 backup-files. So I back up to different folders on the remote storage solutions,
139 based on time. To be more exact, I append the current month to the target
140 directory's name, such that I always have the past 12 versions of my backups
141 (considering that I run backups once every month.): `${HOSTNAME}_$(date +%m)/`.
142
143 However, if you want to keep fewer past versions, there is a little trick via
144 the [modulo](https://en.wikipedia.org/wiki/Modulo) of the current month. Say,
145 you want to keep only the past 3 versions, you can do `$(($(date +%m) % 3))`,
146 which will divide the number of the current month (i.e. 5 for may) by 3 and give
147 you the remainder of 2. So over the course of a year, this calculation would
148 give you 1 in January, 2 in February, 0 in March, 1 in April, 2 in May, 0 in
149 June and so on. This in turn means that you'll always keep the past 3 months as
150 different versions of your backup. Adjust this value to your needs and the size
151 of your remote storage.
152
153 The whole transfer procedure looks like this:
154
155 ```{.sh}
156 #!/usr/bin/env bash
157
158 # How many versions should be kept?
159 TARGET_VERSION=$(($(date +%m) % 3))
160
161 # define target backup storage (here: remote SFTP storage)
162 TARGET="user[AT]my[DOT]remote.backup:${HOSTNAME}_${TARGET_VERSION}/"
163
164 # define directories to be excluded
165 EXCL="--exclude=Downloads/* --exclude=.cache/* --exclude=.var/* --exclude=.local/share/Trash/* --exclude=*.git/* --exclude=.davfs2/*"
166
167 # back up directory
168 rsync \
169 --archive \ # keep ownership information in tact
170 --verbose \ # print more information during transmission
171 --progress \ # show progress of the transmission
172 --delete-delay \ # remove deleted files from target after sync
173 ${EXCL} \ # set exclusion parameters from above
174 "$ENCRYPTED_DIR" \ # source (encrypted mount volume)
175 "$TARGET" \ # remote target (see above)
176 ```
177
178 ## Final touches
179
180 For an easy, semi-automated backup routine, a few additional ease of life
181 improvements come in handy, such as mounting the reverse filesystem before
182 backup and unmounting them afterward.
183
184 Additionally, I like to send desktop notifications whenever I am using the
185 script in a desktop environment. In order to detect this, I use the `$DISPLAY`
186 environment variable for X11 desktops and the `$WAYLAND_DISPLAY` variable for
187 Wayland environments. I typically use `gdbus` to send notifications, wrapped in
188 a shell-function:
189
190 ```{.sh}
191 #!/usr/bin/env bash
192
193 # notification function
194 ## Args:
195 ## 1. Headline
196 ## 2. Notification ID (0 for new)
197 ## 3. icon-name
198 ## 4. Notification text
199 ## 5. additional information ("[]" for none)
200 ## 6. timeout in ms
201 function send_notify {
202 gdbus call --session \
203 --dest=org.freedesktop.Notifications \
204 --object-path=/org/freedesktop/Notifications \
205 --method=org.freedesktop.Notifications.Notify \
206 "$1" $2 "$3" "$1" "$4" "$5" \
207 '{"category": <"im.received">}' $6
208 }
209 ```
210
211 All in all the final script looks like this:
212
213 ```{.sh}
214 #!/usr/bin/env bash
215
216 # configs ------------------------------
217
218 # How many versions should be kept?
219 TARGET_VERSION=$(($(date +%m) % 3))
220
221 # define target backup storage (here: remote SFTP storage)
222 TARGET="user[AT]my[DOT]remote.backup:${HOSTNAME}_${TARGET_VERSION}/"
223
224 # define directories to be excluded
225 EXCL="--exclude=Downloads/* --exclude=.cache/* --exclude=.var/* --exclude=.local/share/Trash/* --exclude=*.git/* --exclude=.davfs2/*"
226
227 # functions ----------------------------
228
229 # notification function
230 ## Args:
231 ## 1. Headline
232 ## 2. Notification ID (0 for new)
233 ## 3. icon-name
234 ## 4. Notification text
235 ## 5. additional information ("[]" for none)
236 ## 6. timeout in ms
237 function send_notify {
238 gdbus call --session \
239 --dest=org.freedesktop.Notifications \
240 --object-path=/org/freedesktop/Notifications \
241 --method=org.freedesktop.Notifications.Notify \
242 "$1" $2 "$3" "$1" "$4" "$5" \
243 '{"category": <"im.received">}' $6
244 }
245
246 # mounting encrypted filesystem --------
247 echo "[INFO] Attempting to mount source as encrypted dir."
248
249 # create temporary directory as encrypted mountpoint
250 ENCRYPTED_DIR=$(mktemp -d)
251
252 # mount home-directory to newly created mountpoint
253 gocryptfs \
254 --ro \ # mount in read-only mode
255 --reverse \ # use "reverse mode"
256 "$HOME" \ # unencrypted directory to be backed up
257 "$ENCRYPTED_DIR" && # temporary mount point
258 echo "$HOME has been mounted in encrypted form to $ENCRYPTED_DIR" ||
259 echo "Mounting $HOME to $ENCRYPTED_DIR failed!"
260
261 # Transfer data ------------------------
262
263 ## send notification
264 if [[ ! -z $WAYLAND_DISPLAY ]] || [[ ! -z $DISPLAY ]]; then
265 send_notify \
266 "BackUpr" \
267 0 \
268 "document-send" \
269 "Starting backup procedure to $TARGET" \
270 "[]" \
271 3000
272 else
273 echo "[INFO] Starting backup procedure to $TARGET"
274 fi
275
276 # back up directory
277 rsync \
278 --archive \ # keep ownership information in tact
279 --verbose \ # print more information during transmission
280 --progress \ # show progress of the transmission
281 --delete-delay \ # remove deleted files from target after sync
282 ${EXCL} \ # set exclusion parameters from above
283 "$ENCRYPTED_DIR" \ # source (encrypted mount volume)
284 "$TARGET" \ # remote target (see above)
285
286 ## send notifications about status
287 if [[ $? == 0 ]]; then
288 if [[ ! -z $WAYLAND_DISPLAY ]] || [[ ! -z $DISPLAY ]]; then
289 send_notify "BackUpr" 0 "document-send" "Backup finished successfully." "[]" 0
290 else
291 echo "[INFO] Backup finished successfully"
292 fi
293 else
294 if [[ ! -z $WAYLAND_DISPLAY ]] || [[ ! -z $DISPLAY ]]; then
295 send_notify "BackUpr" 0 "document-send" "Backup failed!" "[]"
296 else
297 echo "[ERROR] Backup failed!"
298 fi
299 fi
300
301 ## Unmount encrypted file-system
302 fusermount -u "$ENCRYPTED_DIR"
303
304 # EOF backup.sh
305 ```
306
307 ## Restoring a backup
308
309 Restoring the backup is relatively easy as well. For simplicity, I'll assume
310 that the entire backup should be restored. Take a look at `rsync`'s options if
311 that is not what you want. Of course, you can also recover only specific
312 directories or files.
313
314 First off we need the `.gocryptfs.reverse.conf` that the encryption tool created
315 when we initialized the file system for the first time. That file contains meta
316 information about the encrypted storage, but crucially not the decryption
317 password. When mounting the file system, it has been put *unencrypted in plain
318 text* into the encrypted storage as `gocryptfs.conf` and transferred to the
319 remote storage.
320
321 In case you lost your entire local file system and want to restore it from the
322 backup, we first need to fetch this configuration file:
323
324 ```{.sh}
325 #!/usr/bin/env bash
326
327 OLD_HOSTNAME="myoldpc"
328 TARGET_VERSION=1
329
330 scp user[AT]my[DOT]remote.backup:${OLD_HOSTNAME}_${TARGET_VERSION}/gocryptfs.conf \
331 ~/.gocryptfs.reverse.conf
332
333 ```
334
335 Once this is done, we can mount the encrypted file storage again, however this
336 time with writing permissions, so we can restore the files from the remote
337 storage into the encrypted file system:
338
339 ```{.sh}
340 #!/usr/bin/env bash
341
342 # create temporary directory as encrypted mountpoint
343 ENCRYPTED_DIR=$(mktemp -d)
344
345 gocryptfs \
346 --rw \ # mount in read-write mode
347 --reverse \ # use "reverse mode"
348 --config "$HOME/.gocryptfs.reverse.conf" \ # config file
349 "$HOME" \ # unencrypted directory to be backed up
350 "$ENCRYPTED_DIR" && # temporary mount point
351 echo "$HOME has been mounted in encrypted form to $ENCRYPTED_DIR" ||
352 echo "Mounting $HOME to $ENCRYPTED_DIR failed!"
353 ```
354
355 Now we can finally start to transfer the files. They will simultaneously show up
356 as decrypted files in the home directory:
357
358 ```{.sh}
359 #!/usr/bin/env bash
360
361 OLD_HOSTNAME="myoldpc"
362 TARGET_VERSION=1
363
364 # transfer files
365 rsync \
366 --archive \
367 --verbose \
368 --update \
369 user[AT]my[DOT]remote.backup:${OLD_HOSTNAME}_${TARGET_VERSION}/ \
370 ${ENCRYPTED_DIR}/
371
372 # unmount the encrypted storage
373 fusermount -u "$ENCRYPTED_DIR"
374 ```
