You need to Google that. I had that too, some time ago and can’t remember how I solved it, but there are tutorials on the internet. If you find a useful one, I would be delighted, if you’d post it here.
What is the exact command you are using? (including all command line options, etc)
Have you read the corresponding help entry?
adb backup [-f <file>] [-apk|-noapk] [-shared|-noshared] [-all] [-system|-nosystem] [<packages...>]
- write an archive of the device's data to <file>.
If no -f option is supplied then the data is written
to "backup.ab" in the current directory.
(-apk|-noapk enable/disable backup of the .apks themselves
in the archive; the default is noapk.)
(-shared|-noshared enable/disable backup of the device's
shared storage / SD card contents; the default is noshared.)
(-all means to back up all installed applications)
(-system|-nosystem toggles whether -all automatically includes
system applications; the default is to include system apps)
(<packages...> is the list of applications to be backed up. If
the -all or -shared flags are passed, then the package
list is optional. Applications explicitly given on the
command line will be included even if -nosystem would
ordinarily cause them to be omitted.)
If you want to backup your entire Fairphone you will probably need something like adb backup -f backup-file.ab -apk -shared -all -system (Disclaimer: I have not tried this myself yet) This works on my computer (Ubuntu 15.04). I have to insert my encryption password on the phone, and then it backs up.
btw: @longman, were you able to solve your problem? Maybe your solution also helps @mary_k
Just for the record if other people will look this up
Normal adb backup
$ adb backup -all -apk -shared -f foo.ab
And also set a password in the backup settings.
Make sure you the device is found, the password is set and the “backup” dialog shows up!
The backup “dialog” can be see in the xda forum link.
Rooted adb backup
You can get adbd run as root with an app like this or just exchange the adbd binary with one that does not give up root privileges.
It would work like this: Get the right binary** on a sd card. Open a shell, backup the old adbd with mv and relplace it with the the new one. Kill the running old adbd, restart the new one.
(**I think the FP project should provide the right binary and a howto with warnings for people that want to do their own full backup without any extra apps, else you depend on strange adbds from the web.)
If adbd runs as root you could do stuff like backup’ing mms/sms (tested here).