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I am setting up multiple-machine backup plan and I was hoping to use a user called 'backup' on each machine as the backup destination.

My problem is, there is already a user called 'backup' on my machine.

What is it for, and can I hijack it for my own purposes?

root@frodo:~# useradd backup
useradd: user 'backup' already exists
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I can confirm it's in a default installation, see the /usr/share/base-passwd/passwd.master file provided by the base-passwd package.

According to the documentation from that package, it is used for backup accounts without requiring full root permissions (which is available at /usr/share/doc/base-passwd/users-and-groups.txt.gz, /usr/share/doc/base-passwd/users-and-groups.html and online):

backup

Presumably so backup/restore responsibilities can be locally delegated to someone without full root permissions?

HELP: Is that right? Amanda reportedly uses this, details?

Note the keyword locally, for remote backups you have to enable a login shell first. You are free to use it for your own purposes, but note the above guide lines. Do not grant sudo policies for example that would allow the backup user to escalate its privileges to root.

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  • 4
    Unfortunately, that does not really answer the question, whether it is ok to hijack that user or not.
    – ali
    Aug 21, 2015 at 7:28
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    @ali See edit, it is probably fine to use it for your own purposes. A quick scan through Debian Code Search: backup path:debian/ -path:debian/patches/ -path:debian/changelog did not show anything related to the backup user (I stopped at page 8).
    – Lekensteyn
    Aug 21, 2015 at 8:40
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    Slightly concerning that the documenters (still) don't know what it's for either.
    – OrangeDog
    Mar 1, 2021 at 13:58

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