List of all Debian system users and their UIDs

[VA1DER]

Is there a master list of all Debian system users and their UIDs? I want to create a new system user for a script, but before I do I want to see if there is an appropriate one I can reuse. I want to avoid reusing a UID that is used by another system user for software I don't have installed yet.

[GarryRicketson]

Is there a master list of all Debian system users and their UIDs?

Yes there is, it is in /etc/passwd


I used these keywords:

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How to get   List of all Debian system users and their UIDs 

And do find a answer , actually , many very good answers, is your search engine broken ? Did you try that first ?
Since I do understand, in fact just the other day, my favourite search engine was literally broken, for real, I know that can happen, any way the first hit:
Shows various methods, but since you say:

I want to avoid reusing a UID that is used by another system user for software I don't have installed yet.

Probably this is most relevent:

From:https://linuxize.com/post/how-to-list-users-in-linux/Check whether a user exists in the Linux system
/etc/passwd
Now that we know how to list all users, to check whether a user exists in our Linux box we can simply filter the users’ list by piping the list to the grep command.

For example to find out if a user with name jack exists in our Linux system we can use the following command:

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getent passwd | grep jack 

Now I know, you will say, "But I said system users", yes I noticed that, but if you actually can read, and look at the page the link goes to, there is much more, including:

System and Normal Users

There is no real technical difference between the system and regular (normal) users. Typically system users are created when installing the OS and new packages. In some cases, you can create a system user that will be used by some application.

Normal users are the users created by the root or another user with sudo privileges. Usually, a normal user has a real login shell and a home directory.----snip------

It then goes on to show some commands that can be used for "system users" as well,...if that is not enough, try the key words your self, and try reading some of the other results, or maybe sometime someone else will have better answer then this one.
This one is pretty thorough, detailed:
https://www.cyberciti.biz/faq/linux-list-users-command/

[VA1DER]

I meant all system users for all Debian packages, including packages I have perhaps not yet installed. When a Debian maintainer wants to add a new system user, that maintainer must be able to check a list of all UIDs assigned so that the newly assigned user doesn't conflict. I want to know where that list is maintained.

[Head_on_a_Stick]

UIDs are part of the Linux Standard Base:

23.3 User ID Ranges

The system User IDs from 0 to 99 should be statically allocated by the system, and shall not be created by applications.

The system User IDs from 100 to 499 should be reserved for dynamic allocation by system administrators and post install scripts using useradd.

https://refspecs.linuxfoundation.org/LS ... range.html

EDIT: I meant to post this in your other thread (which is about exactly the same thing).

[linuxenthusiast]

I meant all system users for all Debian packages, including packages I have perhaps not yet installed. When a Debian maintainer wants to add a new system user, that maintainer must be able to check a list of all UIDs assigned so that the newly assigned user doesn't conflict. I want to know where that list is maintained.

There are multiple ways of knowing where the user ids may be stored on Linux.

You can indeed check the /etc/password file but there are some files on the filesystem that are also containing entries related to the Name Service Switch (nsswitch.conf)
This is where you might find information about where user ids are stored, sometimes there are stored in NIS for example.