Project

General

Profile

BackupsResearch » History » Version 18

Denis 'GNUtoo' Carikli, 06/08/2020 06:49 PM
Add more rationale for and against adb pull directly

1 1 Denis 'GNUtoo' Carikli
h1. BackupsResearch
2
3
{{>toc}}
4
5 8 Denis 'GNUtoo' Carikli
h2. Introduction
6
7
The [[BackupTheEFS]] page has instructions to backup the EFS. This page instead tries to document why it is done in that way, and what are the advantages and disadvantages of various other backups methods.
8
9 9 Denis 'GNUtoo' Carikli
This can also be useful to write more generic backup instructions to do a more complete backup.
10
11 1 Denis 'GNUtoo' Carikli
h2. Doing the backup of partitions or other block devices
12
13
h3. adb shell cat pipe
14
15 17 Denis 'GNUtoo' Carikli
Old versions of the "EFS backup instructions":https://redmine.replicant.us/projects/replicant/wiki/BackupTheEFS/17 (up to revision 17) used the following command:
16 1 Denis 'GNUtoo' Carikli
<pre>
17 17 Denis 'GNUtoo' Carikli
adb shell "cat /dev/block/platform/*/by-name/EFS" > EFS.img
18 1 Denis 'GNUtoo' Carikli
</pre>
19
20
At some point or under some condition, this stopped working and the backup were corrupted.
21 2 Denis 'GNUtoo' Carikli
22
h3. adb shell cat adb pull
23
24 14 Denis 'GNUtoo' Carikli
With something like that:
25 1 Denis 'GNUtoo' Carikli
<pre>
26 14 Denis 'GNUtoo' Carikli
adb shell "cat /dev/block/platform/*/by-name/EFS > /EFS.img"
27 2 Denis 'GNUtoo' Carikli
adb pull /EFS.img ./
28 1 Denis 'GNUtoo' Carikli
</pre> 
29 2 Denis 'GNUtoo' Carikli
30 18 Denis 'GNUtoo' Carikli
h4. Two steps
31
32
Doing it in two stages like that seem to be widely used in other instructions (like the ones found in XDA forums).
33
34
The advantage is that the '*' enables to use the same command across many more devices.
35
36
And we need two steps because the '*' is not interpreted by a shell when using adb pull:
37
<pre>
38
$ adb pull /dev/block/platform/*/by-name/EFS
39
adb: error: remote object '/dev/block/platform/*/by-name/EFS' does not exist
40
$ adb pull "/dev/block/platform/*/by-name/EFS"
41
adb: error: remote object '/dev/block/platform/*/by-name/EFS' does not exist
42
$ adb pull '/dev/block/platform/*/by-name/EFS'
43
adb: error: remote object '/dev/block/platform/*/by-name/EFS' does not exist
44
</pre>
45
46
This method requires the partition to be small enough. Otherwise it will create several issues:
47
* If the partition is bigger than the RAM, the resulting file in / will end up exhausting all the ram, and the backup will fail.
48
* It instead the partition is big but still fits, doing that would not be very efficient as you would copy the partition once on / to then copy it again through adb.
49
50
h4. dd
51 2 Denis 'GNUtoo' Carikli
52
Normally cat should produce a valid backup, however it might be better to use dd for extra safety.
53
54 10 Denis 'GNUtoo' Carikli
On Replicant 6.0 0004, at least the recoveries for the following devices have 'dd':
55 2 Denis 'GNUtoo' Carikli
* Galaxy Nexus
56
* Galaxy SIII
57
58
h3. adb pull the block device
59
60
The following should also work:
61
<pre>
62
adb pull /dev/block/mmcblk0p3 ./EFS.img
63
</pre>
64 3 Denis 'GNUtoo' Carikli
65 1 Denis 'GNUtoo' Carikli
The advantage is that it can also backup huge partitions like the user data partition or Replicant system partition.
66 10 Denis 'GNUtoo' Carikli
67
TODO:
68
* Validate if doing "adb pull /dev/block/platform/*/by-name/EFS ./EFS.img" work, and if so, validate it for all the devices.
69 15 doak complex
* [by doak] No, it does not (expansion of @*@ fails), but this would do:
70 16 doak complex
<pre>
71
part="`adb shell "ls /dev/block/platform/*/by-name/EFS" | head --bytes=-2`"
72
adb pull "$part" ./EFS.img
73
</pre>
74
Be aware of the @head --bytes=-2@ which is needed to get rid of the nasty @0x0d 0x0a@ line ending returned by @adb@.
75
(Tested on Recovery of Replicant 6.0 0003.)
76 5 Kurtis Hanna
77 11 Denis 'GNUtoo' Carikli
h2. Backup applications.
78
79
It might be a good idea to have a list of backup applications and/or to ship one with Replicant.
80 5 Kurtis Hanna
81
* This backup app might be a good option for Replicant 9 or 10: https://github.com/stevesoltys/backup
82 12 Denis 'GNUtoo' Carikli
* F-droid might also has applications. As F-droid packages are not all FSDG compliant, we would need to make sure that the backup application we recommend or ship are FSDG compliant.
83
84
It might also be a good idea to understand if the backup solution chosen is sustainable in the long term: If the development stop or upstream decide to make the new version proprietary some users might have a hard time adapting to new backup applications or systems.