# Feasibility of using UID > 65535



## priyadarshan (Dec 16, 2021)

Hello,

I need to port a legacy application from Solaris to FreeBSD, heavily dependant on large UIDs. In Solaris, UID can be
up to 2147483647.

In regards to User ID, the Handbook states:



> The User ID (UID) is a number used to uniquely identify the user to the FreeBSD system. Commands that allow a user name to be specified will first convert it to the UID. It is recommended to use a UID less than 65535, since higher values may cause compatibility issues with some software.



How likely is the cited "compatibility issues with some software" aspect?

Can somebody offer some real-world examples where using large UID caused problems?

In respects to pure FreeBSD userland, would one be safe in using UID > 65535? If so, what would then be the upper limit for UID?

Thank you in advance for any clarification.


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## covacat (Dec 16, 2021)

uid_t seems to be 32 bit long
so four billion


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## _martin (Dec 18, 2021)

`uid_t` is the same size on FreeBSD as is on Solaris (unsigned integer, 4B). The handbook is only recommending to use lower UID to avoid possible issues with other SW, such as LDAP. 
As an example imagine you create a local user with uid 400666, you join the system to AD and there will be a remote user with the same UID.
But it's not the limit of the uid_t itself.


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## priyadarshan (Dec 18, 2021)

Thank you for the practical example. It is what I was looking for to better understand handbook's advice.


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