How Many Unix Groups Can A User Be A Member Of?

Question

We've recently run into a situation at a group-happy site where some group memberships are not being picked up. I seem to remember that there is an upper limit to the number of groups that a user can be a member of.

While I am specifically interested in modern Linux systems, I also remember that for some older versions of some OSs that number is lower?

Answer 1

The specific answer seems to be:

• up to 32 on a modern linux
• except if you are accessing a file over nfs, in which case it is 16

...which explains our problem, we've recently crossed the 16-group boundary for some users.

Answer 2

Look for NGROUPS_MAX in limits.h to find the value on your system.

I think this is a tunable parameter in a modern Linux kernel. (Used to be 16 on Solaris, I don't know if they have fixed that yet.)