LSB specifies some group names, but
users is not one of them.
On a completely new setup, you might prefer to avoid using 1000. The way
useradd works, it would allocate each user a group, and the numeric identifiers for user and group id will conveniently end up the same. I would call that the preferred approach for modern multi-user systems (I think older systems defaulted to a shared group like
users as the primary group of the user instead).
My users are not necessarily a member of a shared group like this on either Fedora or Debian. In this case it would be somewhat academic what number is assigned - it would just be another system group which varies between different distributions. (And another group like
bin with no apparent purpose in modern times).
LSB says that UIDs and GIDs 0-99 are statically allocated by the system. UIDs 100-499 (and on all modern systems 100-999) are supposed to be allocated dynamically. This is confirmed by the Debian Policy Manual; it just doesn't have the virtue of being strictly true at the current time.
I'm not really sure what it means that I see It might not be a safe assumption to make, in case the order the groups are allocated in changes for some reason.
users as 100 on a Debian system.
On Fedora, it's pretty safe to assume you can allocate id 100, because the automatic allocation of id's 100-1000 actually counts down. (To be clear, this is the opposite of Debian).
Possible options considering your information so far:
- Stop using the group
users. But probably you have some shared files and you'll need to allocate a shared group ID anyway.
- Use 100 and hope it doesn't break if you [re]install a system that allocates system IDs counting up from 100 like Debian.
- Use something high enough like 10000, which would never end up allocated automatically.
- Use 1000 if none of your existing systems use it for something else and you never plan on adding a new OS which accesses your filesystems.[*]
- Allocate a free ID towards the start of the range 500-1000. (Fedora over five years ago, counted down from 499-100 instead of 999-100, so I can't exclude that you have allocations like that).
[*] Once a system is installed, you can add users with any IDs you want. But my worry is that the initial user created by an OS installer is likely to have ID & GID 1000, not allow you to change them, and particularly if it doesn't create a
root user then changing its ID later can be quite annoying).
The 10000 option sounds simplest to me. It would work nicely if you were ever creating a new system, or instructing someone else. It should also work on your current system.